CHAPTER XXII
CONCLUSION 475
Summary of the argument and of the conclusions.
APPENDIX I 483
Summary of evidence as to restriction of increase amongst Primitive Races.
APPENDIX II 488
LIST OF AUTHORITIES QUOTED 489
INDEX 509
LIST OF ABBREVIATIONS
_A. R. B. E._ = Annual Report. Bureau of Ethnology, Smithsonian Institution.
_A. R. S. I._ = Annual Report of the Smithsonian Institution.
_Am. Anth._ = American Anthropologist.
_Am. Jour. Obstet._ = American Journal of Obstetrics.
_Am. Stat. Ass._ = Publications of the American Statistical Association.
_Ann. de Pal._ = Annales de Paléontologie.
_Ann. Mus. Congo Belge_ = Annales du Musée du Congo Belge.
_Arch. für Anth._ = Archiv für Anthropologie.
_Aust. Med. Jour._ = Australian Medical Journal.
_Biol. Bull._ = Biological Bulletin.
_Bull. Soc. Anth._ = Bulletin de la Société d’Anthropologie.
_C. I. A._ = Congrès International d’Anthropologie.
_Cent. für Min., Geol. und Pal._ = Centralblatt für Mineralogie, Geologie und Paläontologie.
_Coll. Mon. Eth._ = Collection de Monographies Ethnographiques.
_Eug. Lab. Mem._ = Eugenic Laboratory Memoirs.
_Eug. Rev._ = Eugenics Review.
_Geog. Jour._ = Geographical Journal.
_Int. Arch. Eth._ = Internationales Archiv für Ethnographie.
_J. A. I._ = Journal of the Anthropological Institute.
_Jour. Eth. Soc._ = Journal of the Ethnological Society.
_Jour. Pol. Soc._ = Journal of the Polynesian Society.
_Jour. Roy. Agric. Soc._ = Journal of the Royal Agricultural Society.
_J. R. S. S._ = Journal of the Royal Statistical Society.
_Mem. Am. Anth. Soc._ = Memoirs of the American Anthropological and Ethnological Societies.
_Mem. Anth. Soc._ = Memoirs of the Anthropological Society.
_Mem. & Proc. Man. Lit. & Phil. Soc._ = Memoirs and Proceedings of the Manchester Literary and Philosophical Society.
_Mém. Soc. Anth._ = Mémoires de la Société d’Anthropologie.
_Phil. Trans._ = Philosophical Transactions of the Royal Society.
_Quart. Jour. Geol. Soc._ = Quarterly Journal of the Geological Society.
_Q. J. M. S._ = Quarterly Journal of Microscopical Science.
_Rev. Col. Inter._ = Revue Coloniale Internationale.
_Rev. d’Anth._ = Revue d’Anthropologie.
_Rev. d’Eth._ = Revue d’Ethnographie.
_S. I. B. E._ = Smithsonian Institute, Bureau of Ethnology.
_Soc. Rev._ = Sociological Review.
_Trans. Amer. Gyn. Soc._ = Transactions of the American Gynecological Society.
_Trans. & Proc. N. Z. Inst._ = Transactions and Proceedings of the New Zealand Institute.
_Trans. Edin. Obstet. Soc._ = Transactions of the Edinburgh Obstetrical Society.
_Trans. Eth. Soc._ = Transactions of the Ethnological Society.
_U. S. Geog. & Geol. Survey_ = United States Geographical and Geological Survey of the Rocky Mountain Region.
_Z. G. E._ = Zeitschrift der Gesellschaft für Erdkunde.
_Zeit. für all. Erd._ = Zeitschrift für allgemeine Erdkunde.
_Zeit. für Eth._ = Zeitschrift für Ethnologie.
_Zeit. für Morph. und Anth._ = Zeitschrift für Morphologie und Anthropologie.
_Zeit. für Soc._ = Zeitschrift für Socialwissenschaft.
I HISTORICAL
1. Problems of population fall into two main groups—those connected with the quantity and those connected with the quality of the population. Considerations of the population problem are commonly devoted to one of these chief aspects to the exclusion of the other with the result that the relation between them is seldom appreciated. It is one of the objects of this book to show that all problems of population have the same origin. The development of biological knowledge in the last century, and in particular the discussion of evolution, have made it clear that the whole population question and all the problems arising therefrom have their origin in the fact that mankind has a definite position in the animal kingdom. In the next two chapters an attempt is made to set out the basis of the whole question in the light of modern research, and in the fourth chapter are discussed the nature of the various problems and their relation to one another; first those which are connected with the quantity and then those that are connected with the quality of the population.
This was not, however, the manner in which the question was first approached. There was not, to begin with, an understanding of the zoological position of man leading to a growing comprehension of the problems to which it gave rise. From early days attention was particularly directed to the question of numbers. Between the fifth century b. c. and the eighteenth century a. d.—between, that is to say, the time of Plato and that of Malthus—opinions were often expressed regarding the desirability or otherwise of a dense population. The work of Malthus focussed opinion upon this point. In a restricted sense this problem can be solved without an understanding of the biological origin of the whole question, and the discussion which followed the publication of the _Essay on Population_ has resulted in the general acceptance of a solution by students of political economy. In a wider sense the solution of this problem depends upon a comprehension of its biological origin, and it was not therefore until after the middle of the last century that all the problems connected with quantity fell into their proper setting owing to the work of Darwin and Wallace, both of whom acknowledged their debt to Malthus. The latter, though he did not in any way realize the fact, was discussing a point which is most intimately connected with evolution, and both Darwin and Wallace were influenced by their acquaintance with the work of Malthus in arriving at their explanation of the process of evolution. Thus from the time of Darwin and Wallace it has been possible to view the population problem as a whole, though the discussions of the problems connected with quantity have been pursued independently not only before but also after the publication of the _Origin of Species_.
Problems of quality did not arouse the same early interest. It is, of course, well known that Plato was occupied with this aspect of the whole problem;[1] Roman authors also commented upon the eugenic bearing of certain practices.[2] In later days in a remarkable book Campanella dwelt upon the importance of good breeding.[3] But the interest in quality was not, as was the interest in quantity, widespread or long maintained; it was not until the origin of living species by evolution had been generally accepted and some knowledge of inheritance had been gained, that problems of quality came to occupy anything more than the passing attention of mankind.[4] J. S. Mill and Buckle, for instance, both of whose opinions were formed just before the time when the importance of heredity came to be appreciated, deny that it is in any way relevant to the study of social problems.[5]
2. In the preface to the greatly enlarged second edition of his famous book Malthus stated that he had found many references to the subject of which he had not been aware when he published the first volume.[6] He acknowledged that several authors had shown themselves to have possessed a grasp of the ‘principle’ which it was the object of his book to demonstrate. Among these he mentions Plato and Aristotle. In these cases Malthus was too anxious to attribute the first enunciation of the ‘principle’ to others. It was only owing to the very peculiar circumstances of Greek life that the problem ever arose at all. A consideration of the ideal city state involved the question as to what was the most desirable number of citizens. This point occupied Plato’s attention, and in one place he deals with it in detail. There should be, he says, 5,040 citizens in the state.[7] In the _Republic_ he explained that the number of citizens was to be kept about the same by a strict regulation of unions.[8] In the _Laws_, however, no such system is advocated, and he discusses the possibility of a failure to maintain the number.[9] He appears to think that various checks such as infanticide and ‘inundations’ will keep numbers close to the desirable level; if too great an increase takes place, then recourse must be had to emigration. It does not seem that the problem was ever approached more closely in Greek literature.
References to this subject by Roman authors are confined for the most part to laments over the infertility of the old Roman stock. That which drew the attention of the Romans to the subject was thus a peculiar phase of the problem, and the views expressed by them were in consequence usually limited to the search for a remedy for a particular weakness in national life. As we shall point out later, it is doubtful how far infertility was characteristic of all classes; that it was not widespread seems incidentally to be indicated in the following curious passage from Tertullian in which he is led to express views reminiscent of many modern contributions to the subject. Tertullian is confuting the Pythagorean theory of the transmigration of souls, and argues that, if it were true, the number of men must remain unchanged. But, he says, this is obviously not so; population continually increases. This leads him to refer to the state of contemporary civilization. ‘We find’, he says, ‘in the records of the Antiquities of Man[10] that the human race has progressed with a gradual growth of population.... Surely it is obvious enough, if one looks at the whole world, that it is becoming better cultivated and more fully peopled than anciently. All places are now accessible, all are well known, all open to commerce; most pleasant farms have obliterated all traces of what were once dreary and dangerous wastes; cultivated fields have subdued forests; flocks and herds have expelled wild beasts; sandy deserts are sown; rocks are planted; marshes are drained; and where once were hardly solitary cottages are now large cities. No longer are savage islands dreaded, nor their rocky shores feared; everywhere are houses, and inhabitants, and settled government, and civilized life. What most frequently meets our view is our teeming population; our numbers are burdensome to the world, which can hardly supply us from its natural elements; our wants grow more and more keen, and our complaints more bitter in all mouths, whilst nature fails in affording us her usual sustenance. In very deed, pestilence, and famine, and wars, and earthquakes have to be regarded as a remedy for nations, as a means of pruning the luxuriance of the human race.’[11]
3. It is not until we arrive at the sixteenth century that we discover any considerable interest in the matter. From thence onwards references are very frequent. In a general way it is not difficult to understand how this comes about. The movement of thought at that time turned to problems of practical importance. The interest in questions connected with population was above all things due to the problems created by the rise and consolidation of the great European states. In some measure also the voyages of discovery and the foundation of colonies drew men’s thoughts to these questions. It is, as we shall see, in the works of the new class of political writers and theorists, and in the descriptions of travel, that we find most references.[12]
These references take for the most part the form of discussions as to the desirability or otherwise of a large population. There is, indeed, often but little discussion; the benefits of a large population seemed so obvious. Men were mostly of the same opinion as the author of the book of Proverbs, ‘in the multitude of the people is the king’s glory; but in the want of people is the destruction of the prince.’[13] The reasons are not far to seek. A large population appeared to mean both power and riches. The advantage of a large population in supplying a large army proved most attractive and greatly influenced the authors of the eighteenth century.[14] It has not altogether lost its attraction for some people at the present day, as we shall have reason to notice in a later chapter. This simple view of the benefits of a large population coincided with the development of the mercantile theory of trade. Authors of this school of thought also concluded that upon the whole the larger the population the better. Protests against this point of view are, however, met with from time to time. Those responsible for this opposition to the prevailing opinion were influenced in some cases more by observation than by theory and in other cases more by theory than by observation. As instances of the former several English writers of the end of the sixteenth and beginning of the seventeenth centuries may be cited; as instances of the latter several authors chiefly belonging to the later part of the eighteenth century. The views of the last-mentioned authors are often influenced by a conception of the relation between population and subsistence closely similar to that of Malthus. But they are not alone in their anticipation of his position. From the sixteenth century onwards we find in passages dealing with population more or less clear statements of the Malthusian position. These authors, however, are not always led to an unfavourable view of an increase in population. Many of them, indeed, support the current view as to the advantages of large numbers. Nevertheless on the whole a consideration of the connexion between population and the food-supply is usually associated with a fear of increase. We may now review in more detail the trend of opinion sketched above. This will bring us to the publication of the _Essay on Population_.[15]
4. Long before the sixteenth century men gave expression to the view that large numbers are beneficial. ‘Quae familia plus multiplicatur in prolem, amplius cedit ad firmamentum politiae,’ said Saint Thomas Aquinas.[16] But it is only later that we meet with a marked insistence on this view. ‘In my opinion’, says Bodin, ‘they erre much who doubt of a scarcitie by the multitude of citizens and children, when as no cities are more rich nor more famous in arts and discipline than those which abound most with citizens.’[17] According to Botero ‘the greatness of a citty is sayd not to be the largeness of the citty or the circuit of the walls, but in the multitude and the number of the inhabitants and their power’.[18] Machiavelli held very similar views, and Henry IV of France is reported as saying that ‘the strength and riches of kings consist in the number and opulence of their subjects’.[19] In accordance with the views thus widely and strongly held, examples of which might be multiplied almost to any extent, practical measures were taken to encourage the increase of population. Of these the best known is the law of Colbert passed in 1664. Like most of such laws it was modelled on the laws of the later Roman Empire. Similar laws were at one time or another in force in most European countries.
Towards the end of the seventeenth century there arose a school of writers who might be classed as political economists, though the term was not in use. In accordance with the mercantile theory of commerce then predominant a large population was held to be advantageous. The older and vaguer theory that a dense population was necessary if the state was to be powerful was found to coincide with the newer theories as to conditions of prosperous trade. Of these authors Petty and Graunt are celebrated as among the pioneers of statistics. According to the former: ‘fewness of people is real poverty; and a nation in which are eight millions of people are more than twice as rich as the same scope of land in which are but four.’[20] ‘Forasmuch as princes’, says Graunt, ‘are not only powerful but rich according to the number of their people (hands being the father as lands are the mother and womb of wealth) it is no wonder that states by encouraging marriage and hindering licentiousness, advance their own interest, as well as preserve the laws of God from contempt and violation.’[21] Sir Charles Davenant and Sir Josiah Child are two of the foremost authors of this school. The former writes as follows: ‘people are the real strength and riches of a country; we see how impotent Spain is for want of inhabitants with their mines of gold and silver and the best ports and soil in the world; and we see how powerful their numbers make the United Provinces with bad harbours and the worst climate upon earth. It is perhaps better that a people should want country than that a country should want people. When there are but few inhabitants and a large territory, there is nothing but sloth and poverty; but when great numbers are confined to a narrow compass of ground, necessity puts upon them invention, frugality, and industry; which in a nation are always recompensed with power and riches.’[22] The latter refers more than once to the subject. ‘Whatever tends to the population of a country tends to the improvement of it.’[23] ‘Most nations in the civilized parts of the world are more or less rich or poor proportionable to the poverty or plenty of their people and not to the sterility of their lands.’[24] To these quotations we may add one from Sir William Temple: ‘I believe the true and original ground of trade to be a great multitude of people crowded into a small compass of land.’[25]
It would be possible to quote many similar remarks from authors who wrote in the following century. Frederick the Great had very decided opinions. In a letter to Voltaire he says: ‘Je regarde les hommes comme une horde de cerfs dans le pare d’un grand seigneur et qui n’out pas d’autre fonction que de peupler et remplir l’enclos.’[26] Hume speaks of ‘the general rule that the happiness of any society and its populousness are necessary attendants’.[27] Adam Smith says ‘that the most decisive mark of the prosperity of any country is the increase of the number of its inhabitants’. Nevertheless that which interests us most in the authors of this period is the growing interest in other aspects of the subject.
5. Before referring to the more or less close anticipations of the views of Malthus we may note that these optimistic views were not everywhere accepted. In England particularly, towards the end of the sixteenth century, several writers expressed a dread of over-population. According to Holinshed there were some men ‘affirming that we had already too great a store of people in England; and that youth, by marrying too soon, do nothing profit the countrie, but fill it full of beggars, to the hurt and utter undoing (they saie) of the commonwealth’.[28] Later we find Brückner speaking as follows: ‘there are some who believe that a people can never be too numerous and who speak of increase as if it always contributed to happiness, and who consequently continually urge the sovereign to encourage multiplication. The truth of the matter is, however, often far different, depending on the country and circumstances. In a free and enlightened nation, which has great natural advantages, and which is protected from the invasions of less fortunate neighbours, increasing numbers are a good.... In countries not so circumstanced increase is worse than useless; it is, as a matter of fact, impossible, and attempts in this direction can but result in added suffering and an increased number of deaths.’[29] Arthur Young said the same in more emphatic terms. ‘Of all the subjects of political economy I know not one that has given rise to such a crowd of errors as that of population. It seems for centuries to have been considered as the only test of national prosperity. The politicians of those times, and the majority of them in the present, have been of the opinion that to enumerate the people was the only step to be taken in order to ascertain the degree in which a country was flourishing. In my tour through the North of England, 1769, I entered my caveat against such a doctrine, and presumed to assert “that no nation is rich or powerful by mere numbers of people; it is the industrious class that constitutes a nation’s strength”; that assertion I repeated in my _Political Arithmetic_ in 1774.’[30] About the same time Rousseau remarked that ‘il y a pire disette pour un état que celle d’hommes’.[31]
6. In the eighteenth century the problem was often discussed with reference to the connexion between the population and the food-supply. The contrast between the vast possibilities of increase and the smallness of the actual growth in population also often attracted attention. ‘Through various causes’, says Wallace, ‘there has never been such a number of inhabitants on the earth at any one point of time as might have been raised by the prolific virtue of mankind. The causes of this paucity of inhabitants and the irregularity of increase are manifold. Some may be called physical, as they depend entirely on course of nature, and are independent of mankind. Others are moral and depend on the affections, passions, and institutions of men.... To this last we may refer so many destructive wars which men have waged against one another; great poverty, corrupt institutions, either of a civil or religious kind, intemperance, debauchery, irregular amours, idleness, luxury, and whatever prevents marriage, weakens the generating faculties of men, or renders them negligent or incapable of educating their children, and cultivating the earth to advantage. ’Tis to such destructive causes that we must ascribe the small number of men.’[32] Sir James Steuart devotes a considerable amount of space to this subject. ‘The generative faculty’, he says, ‘resembles a spring loaded with a weight, which always exerts itself in proportion to the diminution of resistance; when food has remained for some time without augmentation or diminution, generation will carry numbers as high as possible; if then food come to be diminished, the spring is overpowered; the force of it becomes less than nothing. Inhabitants will diminish, at least in proportion to the overcharge. If, upon the other hand, food be increased, the spring, which stood at 0, will begin to exert itself in proportion as the resistance diminishes; people will begin to be better fed; they will multiply, and in proportion as they increase in numbers, the food will become scarce again.’[33]
Malthus tells us that when he wrote his first edition the only authors ‘from whose writings he had deduced the principle which formed the main argument of the essay’ were Hume, Wallace, Adam Smith, and Price.[34] In the interval between the publication of the first and second editions of the Essay he found that he had been anticipated more or less by many others. Subsequently many other similar passages have been brought to light. It is not worth while to discuss how far Malthus had been anticipated. It is enough to note some of the opinions that had been expressed. In the eighteenth century the fact that there is a connexion between the population and the food-supply had become a commonplace. ‘La mesure de la subsistance est celle de la population,’[35] said Mirabeau, and the remark could be paralleled many times over.[36] Frequent references to the vast power of human increase may be found much earlier. In his _History of the World_ Raleigh had remarked that were it not for wars, famines, pestilences, and so on, a teeming population all the world over would have resulted long ago.[37] Machiavelli refers more than once to the existence of checks. He attributed the barbarian invasions in the later days of Rome to an unusually rapid increase of the tribes beyond the Rhine and the Danube.[38] One of the most interesting references to the subject is to be found in the work of Botero from which we have already quoted. ‘I say, then, that the augmentation of Cities proceedeth partly out of the virtue generative of men, and partly out of the virtue nutritive of Citties. The virtue generative is without doubt to this day the very same, or at least such as it was three thousand years past. So that if there were no other impediment or let therein, the propagation of mankind would increase without end and the augmentation of Citties would be without terme. And if it do not increase in infinite, I must needs say, it proceedeth out of the defect of nutriment and sustenance sufficient for it.’[39] Later on he continues: ‘although men were as apt to generation in the height and pride of the Roman Empire, as in the first beginning thereof; yet, for all that, the people increased not proportionately. For the virtue nutritive of Citties had no power to go further.... By the selfe same reason, mankinde growne to a certain complete number, hath growne no further. And it is three thousand years agone and more, that the world was replenished as full with people as it is at present.’[40]
What are perhaps more remarkable than these references to the relation of numbers to the food-supply, so far as anticipations of Malthus are concerned, are discussions mentioning the ratios which are found from time to time. In the _Primitive Origination of Mankind_, Sir Matthew Hale endeavours to show that mankind must have had a beginning and must have an end, and finds support for this thesis in the facts regarding human fecundity. He calculated that the numbers of mankind must increase in a geometrical ratio unless hindered by checks. Obviously it has not done so chiefly because, owing to absence of sufficient food, large numbers are always being removed by various agencies which he enumerates as plagues, famines, wars, floods, and inundations.[41] Sir William Petty deals with the geometrical ratio at some length. He drew up an elaborate table which, assuming four thousand years to have passed since the flood, shows how an estimated world population of 320,000,000 could have been arrived at.[42] The ratios, however, never played a very prominent part in the discussion until after the publication of Malthus’s book. They reappear now and again, as for instance in a book by Saxe.[43]
7. Malthus published his first edition in 1798. He was born in 1766 at the ‘Rookery’, a country house of some size near Dorking. In 1784 he went up to Cambridge. In early days he had shown signs of ability and at the university fulfilled this promise; he gained some prizes and was placed as ninth wrangler in the mathematical tripos of 1788. In 1793 he was elected fellow of his college, but only resided occasionally. In 1798 he was curate at Albury, close to his birthplace; in 1799 he travelled through Sweden, Norway, and Russia, to collect information for his second edition; in 1802, owing to the Peace of Amiens, he was enabled to travel through Switzerland and France. The second edition appeared in 1803. It was virtually a new book. The four succeeding editions that were published in his lifetime were mainly reprints of this edition with some new matter added. In 1804 he married, and in 1805 became Professor of History and Political Economy at Haileybury College, which post he held until his death in 1834.[44]
It would seem that Malthus and his father used often to discuss new books and questions of the day. His father, Daniel Malthus, was inclined to favour the revolutionary school; Robert Malthus thought that he saw serious objections to Godwin’s views on the subject of ‘perfectibility’, and was so much impressed by them that he decided to put his ideas in writing. Whereas in the first edition Malthus was chiefly concerned with controverting Godwin and his school, by the time of the second edition he had lost interest in this side of the matter and his attention was almost entirely devoted to the problem of population.
Such was the origin of the book which focused the attention of men on the population question. In the sixth chapter we shall have to review the position which it sets out and to trace the subsequent development of the theory. It is sufficient to say here that according to Malthus, whereas population tends to increase in a geometrical ratio, food tends to increase in an arithmetical ratio. As a result population is checked by the operation of vice and misery, to which factors he added, in the second edition, moral restraint. Statistics showed, even in the lifetime of Malthus, that the increase of food was not limited to an increase in an arithmetical ratio, and thus in reality the theory fell to the ground. It was, however, only gradually realized that this was so and that the relation between population and the food-supply is connected with the question of the return to industry, which may at any one time be increasing or decreasing according to the operation of many factors, of which the increase in skill is the chief. The points which are of interest in this historical sketch are the strong feelings which the book aroused among the adherents of the various schools of thought, the practical movement to which it gave shape, and finally the influence which it had upon Darwin and Wallace.
8. From what has been said, it is clear that the ground had been well prepared for a favourable reception. Further the ‘populousness of ancient nations’ was a famous theme for controversy in the eighteenth century. There had also been much discussion as to whether the population of England was increasing or decreasing.[45] Again, in part owing to the industrial revolution, and in part owing to the war, questions as to poverty had attracted much attention, and to them Malthus’s book had direct reference. Thus it is not surprising that the success of the first edition was great and immediate.[46] Godwin admitted that it had ‘converted friends of progress by the hundred’.[47] Pitt dropped his Poor Law Bill in 1800 partly because of the opposition of those who had been influenced by the Essay. The earlier supporters of Malthus belonged, for the most part, to the Whig and Utilitarian schools. Pitt, Paley, Copleston, James Mill, Senior, Ricardo, Macintosh, and Whitbread all adhered to Malthus. In 1819 Brougham referred to the ‘principle of population as one of the soundest principles of political economy’.[48] Support for Malthus was especially strong among the Utilitarians. Referring to about the year 1825 J. S. Mill says: ‘Malthus’s principle was quite as much a banner and a point of union among us as any opinion especially belonging to Bentham.’[49]
Opposition was chiefly to be found among the Tories, Revolutionaries, and Radicals. Godwin published a reply to Malthus in 1801, and several years later, finding that the ‘principle’ still gained ground, made another attempt to refute it, which met with as little success as the earlier attempt. As an example of the attitude of the followers of Godwin towards Malthus, the following remarks by Shelley may be quoted. ‘Metaphysics and inquiries into moral and political science have become little else than vain attempts to revive exploded superstitions, or sophisms like those of Mr. Malthus, calculated to lull the oppressors of mankind into a security of everlasting triumph.’[50] The Tory element of the opposition was influenced by the feeling that the ordering of human affairs could not be so innately bad as the Essay seemed to suggest.[51] Southey and Coleridge represent this view; the former attacked the Essay more than once with considerable violence.[52] Cobbett made himself prominent among the critics by inventing the sobriquet ‘Parson’ Malthus. It occurs in the following passage.
‘Why,’ said I, ‘how many children do you reckon to have had at last?’
‘I do not care how many,’ said the man, ‘God never sends mouths without sending meat.’
‘Did you never hear,’ said I, ‘of one Parson Malthus?’
‘No, sir.’
‘If he were to hear of your works, he would be outrageous, for he wants an Act of Parliament to prevent poor people from marrying young, and from having such lots of children.’
‘Oh, the brute,’ exclaimed the wife, while the husband laughed, thinking I was joking.[53]
Hazlitt, who may be classed as a radical, was one of the most violent of the opponents. Indeed, as Mr. Bonar says, ‘Malthus was the best abused man of his age.’[54]
The Essay early became known on the Continent. As far as Germany was concerned, this was attributable, according to von Mohl, to a work by Luden.[55] During the lifetime of Malthus the violence of the opposition gradually weakened and the principle was very generally accepted. For many years such opposition as there was was based rather on religious grounds than upon an understanding of true weaknesses of the theory. Nevertheless Sumner, who was afterwards Archbishop of Canterbury, and Thomas Chalmers in early days both proclaimed their adherence to the principle.[56] In 1840 three books were published which each attacked the principle on religious grounds. Of the authors, Sadler was a Churchman without apparently any strong political feelings, Alison a Tory, and Doubleday a Radical.[57] That the religious motive continued to inspire opposition may be gathered from an essay by W. P. Greg which appeared at a much later date.[58]
It may be noticed that strong opposition was nearly always exhibited to the views of Malthus by socialistic authors.[59] According to Proudhon, ‘la théorie de Malthus, c’est la théorie de l’assassinat politique, de l’assassinat par philanthropie, pour l’amour de Dieu.’[60] Karl Marx in a well-known passage attacked Malthus in most violent and offensive language.[61]
9. As a result of the Essay, there began within the lifetime of Malthus the advocacy of Neomalthusianism. Malthus himself definitely disapproved of this practical application of his ‘principle’.[62] The practical application of which he approved was made by Miss Martineau in one of her _Illustrations to Political Economy_, which reads so strangely at the present day.[63] As regards Neomalthusianism it is very generally supposed that active propaganda only began about the time of the famous Bradlaugh-Besant trial in 1876. This, however, is a complete mistake.[64] The first publication of importance in which these ideas were put forward was an article by James Mill in the _Encyclopaedia Britannica_. His language was very guarded but the drift of his remarks unmistakable. Four years later, in 1822, Francis Place wrote a reply to Godwin. He covered much other ground but openly and deliberately advocated these practices. For the next ten years there followed an active propaganda. The events which first brought the whole question into public notice are somewhat curious. In 1823 a number of handbills were sent to Mrs. Fildes, well known in the North for her work among the poor; these bills contained descriptions of the methods which the new school of writers wished to see adopted by the working classes; an anonymous letter accompanied them asking her to help in distributing them. Mrs. Fildes was very indignant, and the whole story was published in the journal called the _Black Dwarf_. The bills attained a great notoriety and became known as the ‘diabolical handbills’. Suspicion seems to have rested upon Robert Owen; it was stated in the _Black Dwarf_, and has often been repeated since, that Neomalthusian methods were in use at New Lanark. It is far more probable that Francis Place was the author both of the handbill and of the letter. Whether this is so or not, Place was occupied for the next few years in doing all he could to spread the new opinions, for the sake of which he was prepared to sacrifice much popularity.[65] In 1834 the Society for Promoting Useful Knowledge refused his help because of his opinions on the subject. He was violently attacked by Cobbett and Richard Carlile; the latter was afterwards converted and published in 1825 articles advocating these practices. The articles were reprinted in 1826 as _Every Woman’s Book_, which went through several editions. At this early date it is clear that on the one hand these books and pamphlets were widely read among the working classes; Carlile in the _Republican_, for instance, asserted that they were ‘circulating by thousands in the populous districts of the north’. On the other hand Neomalthusian ideas were held by many eminent men of the day. The Utilitarian leaders, if not actually concerned in the propagation of these views, made their approval known. J. S. Mill in his youthful days got into trouble with the police through distributing some of these pamphlets. Grote somewhat later presented to London University a copy of the famous _Fruits of Philosophy_, of which there will be more to be said below.
After a while the propaganda died down, and for some fifty years there was little heard of it.[66] Some books were, however, published in the interval which subsequent events made famous. R. D. Owen’s _Moral Physiology_ appeared in 1830. Knowlton’s _Fruits of Philosophy_ and Drysdale’s _Elements of Social Science_ appeared in 1833 and in 1854 respectively. It was many years, however, before they became well known. For many years no objection was taken to the _Fruits of Philosophy_, or any similar work; such books were allowed to circulate freely. In 1876 a Bristol bookseller, Cook by name, was condemned to two years’ imprisonment for selling an illustrated edition of Knowlton’s work. Soon after another bookseller was also fined. Thereupon Mr. Bradlaugh and Mrs. Besant determined to take up the subject and fight for what they considered to be the right of freedom of discussion in these matters. They had an edition of the _Fruits of Philosophy_ printed, and took a small shop where it was openly exposed for sale. A prosecution followed. In 1877 they were tried before Sir Alexander Cockburn, the Lord Chief Justice; the Attorney-General prosecuted. The summing-up was distinctly in favour of the accused; the jury, however, returned a verdict of guilty, adding a rider to the effect that they considered the defendants to be innocent of any immoral intention. Judgement was reserved. But in the interval Mr. Bradlaugh and Mrs. Besant continued to sell the book, and the result was that, instead of merely being bound over, as had been the intention of the judge, they were condemned to six months’ imprisonment and to a fine of six hundred pounds. The judgement was subsequently quashed in a higher court.
The trial was a huge advertisement for Neomalthusianism. For some years spasmodic efforts to punish the sale of Neomalthusian books only served to encourage the propagandists. In 1877 the ‘Neomalthusian League’ was founded and a vigorous propaganda was carried on. The activity of the league in England gradually declined, but not before the movement had spread to foreign countries. Propaganda in other countries followed a very similar course; in 1888 there was a trial in Australia which is as famous in that country as the Bradlaugh-Besant trial in England. Prosecutions occurred in India and in America. In 1891 a remarkable dispute took place in Norway, and a law was finally passed to prohibit the sale of Neomalthusian books. As lately as 1908 a Belgian doctor was condemned to imprisonment for spreading the knowledge of Neomalthusian methods.[67]
10. With this notice of the history of the development of Neomalthusianism we may leave this side of the subject. The history of speculation regarding evolution has been so often described that there is no need to go into the facts here.
It is well known that before Darwin and Wallace turned their attention to the subject, the origin of organisms by evolution as opposed to origin by separate acts of creation had often been suggested. There was already at the beginning of the nineteenth century a considerable accumulation of facts regarding the structure and relation of organisms to one another and regarding the fossil remains of organisms. This evidence was seen to point to evolution as against creation, but until Darwin and Wallace produced their theories no one had been able to formulate a satisfactory hypothesis as to how evolution could have come about. It is of great interest to observe that it was after reading Malthus that both Darwin and Wallace independently formulated their theories. Malthus had, in fact, when taking up for consideration the quantitative aspect of the problem, so far as man was concerned, been dealing with that class of facts upon which, not only the quantitative, but also the qualitative aspect of the problem is based. When Darwin and Wallace, with the problem of evolution before them, which is essentially the problem of quality—the problem of the manner in which one type of organic form can be derived from another type—chanced to read Malthus, their attention was called to the class of facts connected with the birth-rate, the death-rate, and allied phenomena. They realized that among species in a state of nature a somewhat similar state of things existed to that which Malthus, with another aspect of the problem in view, was investigating in the case of man, and from a consideration of these facts they founded independently the hypothesis of natural selection.
It is of interest to note what Darwin and Wallace themselves say as to their indebtedness to Malthus. In a passage in the well-known autobiographical sketch Darwin writes as follows: ‘in October 1838, that is fifteen months after I had begun my systematic inquiry, I happened to read for amusement Malthus’ ‘Population’, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of animals and plants it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of a new species. Here then I had at last got hold of a theory by which to work.’[68] In two letters that have been published—one to Haeckel[69] and one to Wallace[70]—Darwin also recorded in very similar words his debt to Malthus, and in the _Origin of Species_, after describing what is meant by the struggle for existence and how it comes about, says, ‘it is the doctrine of Malthus applied with manifold force to the animal and vegetable kingdoms.’[71] So too Wallace, in his reply, after having been presented with the first Darwin-Wallace medal by the Linnean Society in 1908, acknowledged his debt to Malthus in the following words: ‘both Darwin and myself, at the critical period when our minds were fully stored with a considerable body of preserved information and reflection bearing upon the problem to be solved, had our attention directed to the system of positive checks as expounded by Malthus in his _Principle of Population_. It is an unimportant detail that Darwin read this book two years after his return from his voyage, while I read it before I went abroad and it was a sudden recollection of its teachings that caused the solution to flash upon me.’[72]
Since the publication of the _Origin of Species_ much attention has been paid to the problem of quality as regards the human race. It was obvious that if the human race had evolved from some lower type, it was probably still in process of evolution, and that the direction of evolution was by no means necessarily upwards. It was also obvious that the further evolution of the race was to some extent at least within human control, if and when men chose to use the means of control that lay within their power. Great impetus was given to this side of the problem by the work of Sir Francis Galton, who coined the word ‘eugenics’.[73] Societies for the study of eugenics and for the advocacy of eugenic ideals have been started in England, in many European countries, in America and elsewhere, and at the present day the educated classes in every country are at least aware of the existence of the problem of the quality, as they have long been aware of the existence of the problem of the quantity, of population.
The development of opinion on this subject has thus run a peculiar course. Attention was drawn in early days to the existence of the problem of numbers, but men were long satisfied with asserting on comparatively simple grounds that a dense population was desirable or undesirable, and they usually came to the conclusion that the more inhabitants in a country, the better for the country. Long before the time of Malthus, and by many different writers, attention was paid to the connexion between numbers and the food-supply. It was Malthus, however, who first aroused public interest in the subject. His book, indeed, made an impression that few books have ever made. Since his time every educated man has had the problem of numbers in mind, and current opinion still often enough reflects the view put forward by Malthus if not in detail—for it is difficult to say what exactly the views of Malthus were—at least in the general and on the whole gloomy and fatalistic manner of regarding the problem. It is owing to the fact that those contributions which, after the time of Malthus, attracted most attention, added little to the development of thought, and owing to the influence of the writings of J. S. Mill, who himself never shook off the profound impression made upon him early in life by the Essay, that the views, or perhaps we should rather say the outlook, of Malthus so long maintained their sway. The development of the modern view as expounded by political economists was not set out in a form that attracted public attention, and it was thus possible for the late Governor of South Africa, when answering a question in the House of Commons a few years ago, to refer to the problem as though no important contribution had been made to the subject since the time of Malthus.
Of the development of opinion regarding the qualitative aspect of the problem there is little to be said. Popular interest in this subject is of comparatively recent birth. That which is interesting to observe is that, as a result of the course which thought has taken, the population problem is seldom seen as a whole, and that the relations one to another of the very numerous questions arising therefrom are scarcely ever appreciated.
II THE BASIS OF THE POPULATION PROBLEM: (1) THE QUANTITATIVE ASPECT
1. In what follows the evolutionary position is taken for granted. It is assumed, that is to say, that the higher forms of life have evolved from lower forms. If we make this assumption, we must suppose that at one time the ancestors of man were living under those conditions to which species in a state of nature are now subject. By species in a state of nature are meant all species of animals and plants with the exception of man and those species which have been domesticated by him. It is the object of this and the following chapter to show that among species in a state of nature the population problem exists both in its quantitative and qualitative aspects, and further that in certain particulars of fundamental importance the position is the same for all such species. Certain propositions may be laid down which hold good for any one of them, and in these chapters it is proposed to show what it is that may be affirmed with regard to all of them. It follows that, since among the ancestors of man the population problem must at one time have taken this form, we shall, as the result of the discussion, arrive at a basis from which we can proceed to study the shape which the problem in its double aspect has assumed in the case of man.
It is necessary to emphasize the fact that this argument does not take the form of developing an analogy between the position of man and that of species in a state of nature. What we are doing is merely to attempt to ascertain the conditions under which the ancestors of man lived, in order that we may follow the changes which have taken place. Further, it may be well to point out that the argument in these chapters will follow rather an unusual course. It may seem that certain facts of considerable general importance are passed over and others of little obvious importance emphasized. The justification for this course will be apparent later when we come to deal with the position with regard to man; for this sketch is not introduced primarily with the object of throwing light upon the position of species in a state of nature, but in order to prepare the way for a discussion of the shape which the problem has assumed in the case of man.
2. At the basis of both aspects of the problem lies the fact of reproduction. All organisms reproduce their kind. Reproduction is clearly a necessity, because all living things are liable to meet death by accident and, unless there was reproduction, every species would soon be extinguished. It is worth while observing that among all higher forms of life a more or less clearly defined limit to the duration of life has been evolved. In other words, natural death after a certain period ensues. It would seem that natural death has been evolved in the following manner. All organisms are subject to the wear and tear of daily life, to meet which there is a faculty of recuperation. Among the lower forms this faculty is very pronounced. The whole animal can be regenerated from a small fragment and, as a result, very serious accidents are not fatal. Among the higher forms there goes, generally speaking, with the advance in structure a loss of the power of regeneration, until among the highest there is little or no power of regeneration; for a certain average length of time the highest organisms withstand the batterings of daily life, gradually fail to recuperate, and finally die. Given the necessity of reproduction to provide for the continuance of the species against accident to its members, this further evolution is not difficult to understand. A power of recovery from all but the most extreme forms of accident is present among the simpler types; the retention of such a power of recovery tends to be incompatible with increasing complexity of structure, and it has, so to speak, been more economical to evolve organisms provided with a power of recuperation only against normal wear and tear over the period during which they remain capable of reproduction. The higher types therefore, after reproducing their kind, die and thus the battle of life is always being resumed by fresh generations.
3. That in some such fashion reproduction has to be explained seems clear; but we are concerned here with the facts of reproduction. It will be necessary later to go into the nature of reproduction in greater detail; all that needs to be said here can be stated quite shortly. There are two forms of reproduction, known respectively as the sexual and asexual; the latter type of reproduction occurs only among plants and the lower animals. As sexual reproduction occurs among all groups of animals and plants, whether asexual reproduction occurs or not (except among the bacteria where the latter type alone is known) and as it is the only type which occurs among the higher groups, asexual reproduction may be disregarded here. The asexual type of reproduction, it may be remarked, introduces no new principle, and those groups among whom it is found are not on that account to be set apart from other groups as though the general conclusions at which we shall arrive were not applicable to them.
To make the process of sexual reproduction clear it is necessary to say something regarding the structure of organisms. Excluding the Protista for the moment, all organisms exhibit a cellular structure. Upon examination under a microscope the living tissues are found to consist of a number of compartments or cells. Among plants the typical cell is in the nature of a small box with thick sides; among animals the sides or cell-walls are very thin. Within the cell-walls there are to be distinguished two chief elements, a central body, the nucleus, and the surrounding cytoplasm. This cytoplasm consists of ordinary granular protoplasm and the nucleus of a special kind of protoplasm. Only protoplasm can properly be spoken of as alive. Those elements in the body which are not protoplasm are either in the course of being turned into protoplasm or are the products of protoplasmic activity. Examples of the latter in man are the hair and the nails, and in the case of other animals, feathers, shells, and so on. As a general rule, each cell contains a single nucleus, but there are cells without a nucleus and cells with more than one nucleus. The name Protista, mentioned above, is given to the lowest animals and plants which are commonly said to consist of a single cell. They may be thus thought of; but the group includes forms with many nuclei of which it can only be said that cell structure has not yet been differentiated. It is therefore possible that the term cell should not be used at all in respect of this group.
Among the Protista sexual reproduction takes very different forms. Essentially, however, it consists in the fusion of two individuals, and if we regard each individual as a cell, it may be said to consist in the fusion of two cells. Among the higher forms the essential feature of sexual reproduction is the same; it consists, that is to say, in the fusion of two cells. It no longer consists in the fusion of two individuals, but in the fusion of two cells, one given off by one individual, and one by the other.
The manner in which these cells, known as gametes, are given off by the male and the female and the manner in which they fuse require some further explanation. What happens in plants is in all important features similar to that which happens among animals, and we may confine our attention to the latter. In every normal member of every species there is a generative organ.[74] It consists of a surrounding wall within which is a mass of developing germ-cells. In the female the fully developed gamete, called the egg or ovum, is, relative to the male gamete, of large size. It is typically a motionless cell containing a varying quantity of food substance which may, as in the case of the bird’s egg, reach a large amount. The male gamete is a much smaller cell. With a few exceptions it consists of a small oval-shaped head, to which is attached, by means of an intervening neck or middle-piece, a long vibratile tail. The head is the nucleus of the cell; if there is any cytoplasm, it is reduced to a very small amount and its presence cannot be readily demonstrated.[75] In strong contrast to the ovum the spermatozoon is typically motile and can swim in those fluids in which fertilization usually takes place.
Fertilization consists in the penetration of an ovum by a spermatozoon. The tail does not always enter the egg; as soon as the head has entered, a change takes place in the egg which sometimes prevents the tail, and usually other spermatozoa, from entering the egg. The head or nucleus of the spermatozoon approaches the nucleus of the egg and fuses with it. At this point, therefore, we have a single cell, known as the zygote, formed by the fusion of two cells, one derived from the male and one from the female. The zygote grows and divides and ultimately gives rise to an adult; into this process of growth it is not necessary to go for the moment. The zygote is to be regarded as a new member of the species the existence of which dates from the fusion of the two nuclei. Whether the zygote lives an independent existence from the beginning, or is retained within the body of the mother for a longer or shorter period, is immaterial so far as the dating of the beginning of the existence of a new individual is concerned. Every man and woman is thus in reality some nine months older than his or her nominal age.
4. Such are the essential features of the process of sexual reproduction through which new members of the species arise. We have now to consider the outward features of the process, which vary very considerably. So various are they, that at first sight it may scarcely seem likely that there is any fundamental generalization that can be made regarding the process as a whole among all species in a state of nature. When we have glanced at the facts and at their interpretation we shall be in a position to discuss what it is that holds good for all such species.
Among all multicellular animals and plants the number of spermatozoa produced is infinitely greater than the number of ova. A single normal sexual emission in man is said to contain about 226,000,000 spermatozoa. This immense production of male gametes makes it likely that a male gamete will meet and fuse with each female gamete. Among the higher animals there are certain instincts which further ensure that the male cells will be brought into the proximity of the female cells. Among other multicellular animals and plants there are no such instincts. Generally speaking, among the latter types fertilization may be thought of as fortuitous. In anemophilous plants, for example, such as the Pines, the male cells or pollen-grains are specially adapted so that they are caught and carried by the wind for long distances. Many million times more male cells than female cells are formed in these plants, and some of them, wafted by the wind, eventually light upon the ovule. So too among such lowly animals as the sea-urchin the male and female cells are extruded into the surrounding sea-water; as these animals live close together, and as the male and female cells ripen and are extruded at the same time, the chance that any egg will remain unfertilized is small, the number of the active spermatozoa being so many times greater than the number of eggs. This simple form of fertilization is characteristic of most plants and of many animals. In plants there are certain complications, in particular those connected with fertilization with the help of insects, into which it is not necessary to go.
The increasing complexity of animal structure is only roughly correlated with increasing complexity in the processes connected with fertilization. Though the most complex form of the process is found among the highest animals, yet some animals, which stand relatively high in the scale, exhibit a simple method of fertilization. Of this the fish are an example, and, further, the more highly developed or bony fish exhibit a simpler form than some of the more lowly-organized cartilaginous fish. In fact, the stage next above that of which the sea-urchin was given as an example can be illustrated from the bony fish. The process in this group consists in the approach of the male to the female alongside of whom he swims, led by a rudimentary development of the sexual instinct. When the female ejects her gametes into the water, the male does the same and the vastly greater number of the male gametes ensures that all or nearly all of the eggs are penetrated by a spermatozoon.[76]
The next stage is that characterized by external copulation. The male clasps the female and when the latter ejects her eggs, he extrudes his spermatozoa at the same time. The meeting of the gametes thus still takes place outside the body of the female. This form of fertilization is found among the Amphibia; the male frog, for example, has specially developed pads on his front feet with which he embraces the female. Internal copulation, though it is to be regarded as the most complex form of the process, is found among such low forms as flat worms,[77] of which the common tapeworm is a member, among many higher Invertebrates such as snails and insects, as well as among cartilaginous fish, birds, and mammals. The essential feature of internal copulation is that the male is provided with a special copulatory organ or penis which he inserts into the female. The male gametes pass through the penis, which takes the form of a tube, directly into the body of the female, and fertilization thus takes place within the body of the female.
5. When fertilization takes place without copulation it might be thought that a small proportion of eggs only would be fertilized, that, so long as fertilization, for instance, depends on the wafting by the wind of a pollen-grain over a considerable distance until it alights on one small spot, or upon the chance meeting of a spermatozoon and an egg in the water, there would be but a small proportion of eggs fertilized. This, however, is not so; observation shows that in a state of nature failure is comparatively rare, and that the majority of female gametes are fertilized. This is in the main due to the vast number of male cells compared with the number of eggs. Among those forms in which copulation takes place, fertilization is clearly dependent upon the strength of the sexual instinct, which impels the male to seek the female. That this instinct is very powerful is well known. It may for the time overcome all other instincts. There is a frenzy of desire among many animals. Male frogs and toads will remain clasping the female for many days waiting for the extrusion of the eggs. Female toads have been discovered smothered by the male in the sexual embrace.[78] It has been noticed that birds, which under usual circumstances are frightened by the sound of a gun, will take no notice when in pursuit of a female.[79] All the evidence points to the fact that, owing to the strength of the sexual instincts, females are rarely left undiscovered by a male in the sexual season. Jenner records that one of a pair of magpies was killed and that on the following day the survivor appeared with another mate. One of this pair was killed and on the next day the survivor again appeared with another mate. This was repeated for seven days and on each occasion the survivor always appeared with a new mate.[80] In this connexion the great development of those forms of secondary sexual characters may be referred to which enable the two sexes to find and recognize one another. Such are recognition marks, call-notes of many insects, birds, and mammals, and the strong odours given off by many animals during the sexual period.
Generally speaking, the male is always prepared for the act of copulation and the act takes place when the female is ready to receive the male. This is so among mammals whether the male experiences a sexual season known as the ‘rut’, as among stags, or whether he does not, as among dogs; for the period of ‘rut’ lasts longer than the period during which the female is ready to receive the male. The facts, however, regarding the sexual season in mammals are somewhat complicated owing to the nature of the sexual season experienced by the female. A number of different types of mammalian sexual season have been distinguished; it is not necessary, however, to go into these distinctions. It is sufficient to say that each sexual season consists of one or more sexual cycles, known as oestrous cycles. An oestrous cycle may be divided into four periods; the first, known as the pro-oestrous, is the period of preparation which ends in the rupture of the blood-vessels in the mucous membrane of the uterus. When the blood passes to the exterior, it is known as the menstrual flow. The second period or oestrous is the period of desire. This period is always short; in the sheep it lasts about twelve hours and often in other species does not last as long. Only during this latter period will the female receive the male;[81] copulation never takes place at any other period, and yet in spite of the fact that the opportunity for copulation is narrowly restricted, so strong is the sexual instinct in the male, that it is very rare for a female, so far as observation goes, not to engage in copulation at each oestrous. The period of oestrous is followed by the period of metoestrous during which the activity of generation subsides, and the metoestrous is followed by the anoestrous or period of rest, after which another pro-oestrous period begins a new cycle.
The period of oestrous, during which copulation takes place, is usually marked by the presence of ripe female gametes which are therefore at once fertilized. Ripe ova are, however, not always present at oestrous; in the rabbit ovulation takes place an hour and a half after copulation. In the bat there is a very marked want of coincidence between oestrous and ovulation; copulation takes place in the autumn, but ovulation does not take place until the following spring. In such cases the spermatozoa remain alive in the uterus until the female gametes are ripe, when fertilization is achieved; thus in the bat the spermatozoa remain alive for several months. When such cases occur, therefore, it does not mean that the ova are not fertilized. In the monkeys, however, ovulation may occur independently of oestrous and in such a manner that the ova then liberated may not be fertilized.
What has so far been said all goes to show that the majority of ripe ova are always fertilized among species in a state of nature. There must be a certain number of failures among those species which copulate, as when a mammalian female, as must now and again happen, does not engage in copulation during oestrous. Among species which do not copulate, failures are doubtless more frequent. There is probably a greater wastage of eggs when they are adhesive and fixed to some object than when they are pelagic, as is most often the case among marine animals; for when eggs are adhesive the seminal fluid may drift away.
We are now approaching a point at which it is possible to establish the first generalization regarding the process of reproduction among species in a state of nature. It is, however, not possible to make clear what it is intended to convey until something has been said regarding animal behaviour. Some of the most striking differences between one class of animal and another as regards the process of reproduction are connected with the evolution of animal behaviour. So far we have spoken of instinct without defining what is meant, and until something has been said regarding the course and limit of mental evolution among animals, the nature of the common element in all forms of reproduction among all species in a state of nature and the manner in which it differs from what is found among men cannot be set out. It may seem that the following review is taking us somewhat out of our path. It so happens, however, that in view of the questions that will come up later for discussion, such a sketch will be necessary and it may therefore be now undertaken so as to render further amplification unnecessary.
6. Putting aside the behaviour of plants, we find among the lower animals a type of behaviour which, though simple in a certain sense, cannot be adequately explained without a prolonged discussion. Some idea can be obtained of its nature if we consider in what a reflex action consists. When a definite and simple stimulus is followed directly by a definite and simple reaction we have what is called a reflex action. This term, it may be noticed, is usually restricted to cases where a nervous system is present. When similar reactions occur among organisms in which the nervous system has not been differentiated, it has been suggested that the term ‘autotype’ should be used.[82]
Reactions, however, probably never follow invariably upon the repetition of the same stimulus. Among the lowest class of animals, the Protozoa, a free-swimming ciliate Infusorian, will, if it comes into contact with something in the medium which is abnormal, it may be, for example, an alkaline solution, stop and go backwards. This is an example of a reflex action. An analysis of its subsequent movements shows that, if it again and again meets the alkaline solution, some modification of the reaction takes place. The animal may show increased activity until either it is overcome by the disturbing medium or it has freed itself from it. So again after the digestion of food, such an organism shows a different response to the presence of food.
More definite instances of different reactions following upon the same stimulus are provided by experiments of changing the nature of the medium. An Infusorian will react violently against certain new elements in the medium to which after a time it becomes habituated, when the reaction no longer follows. Very interesting experiments have shown that even among the simplest class of organisms there is a certain learning from experience. ‘A Stentor (one of the ciliate Infusorians) if gently touched upon one side will contract upon its stalk, but will soon open out again. Touched once more, it will perhaps bend to one side, and if continually molested in this manner, it will uproot itself in pardonable dudgeon and swim away. That is to say it has several ways of reacting to the stimulus and seeking equilibrium, and, if one fails, it tries another. But now when it anchors itself again, it seems to have learnt something, for if again touched it does not go through the stages of contracting and of bending aside. It keeps to its more radical remedy and moves off again.’[83] It is doubtful whether there is any further complication of this type of behaviour among organisms which do not attain to the kind of behaviour that we have now to describe.
7. Herbert Spencer, as is well known, defined instinct as compound reflex action. Though this definition cannot, for various reasons, be accepted as adequate, it does suggest the essential nature of instinct, which consists in the response to a given but often vague stimulus of a more or less complicated series of reactions. Instinct is more than compound reflex action because it involves the organism as a whole, and is accompanied by, or is the outcome of, a mental process. All mental process is said to involve three aspects—the cognitive or the knowing of an object, the affective or feeling in regard to an object, and the conative or striving to or from an object—and these three aspects are to be found in all instinctive actions. The instinctive action is initiated by a sense-impression and is followed by results so important because the nervous system is innately organized to respond to certain sense-impressions. It is presumed that some kind of emotional excitement, however faint, always follows and that it gives rise to the striving that we see in the form of movement. Instinct has been defined as ‘an inherited or innate psychophysical disposition which determines its possessor to perceive and to pay attention to objects of a certain class, to experience an emotional excitement of a particular quality upon perceiving such an object, and to act in regard to it in a particular manner, or, at least, to experience an impulse to such action’.[84]
Every one is acquainted with many examples of instinctive action. ‘There are many instances of insects that invariably lay their eggs in the only place where the grubs, when hatched, will find the food they need and can eat, or where the larvae will be able to attach themselves as parasites to some host in a way that is necessary to their survival. In such cases it is clear that the behaviour of the parent is determined by the impression made on its senses by the appropriate objects or places: e. g. the smell of decaying fish leads the Carrion fly to deposit its eggs upon it; the sight or odour of some particular flower leads another to lay its eggs among the ovules of the flower, which serve as food to the grubs. Others go through more elaborate traits of action, as when the Mason-wasp lays its eggs in a mud nest, fills up the space with caterpillars, which it paralyses by means of well-directed stings, and seals it up; so that the caterpillars remain as a supply of fresh animal food for the young which the parent will never see and of whose needs it can have no knowledge or idea.’[85] To take some examples from among the Vertebrates, ‘pheasants, plovers, moor-hen, domestic chicks and ducklings, with many others, are active soon after birth, and exhibit powers of complex co-ordination, with little or no practice of the necessary limb movements. They walk and balance the body so soon and so well as to show that this mode of procedure is congenital, and has not to be gradually acquired through the guidance of experience. Young water birds swim with neat orderly strokes the first time they are gently placed in the water. Even little chicks a day or two old can swim well.’[86]
Enough has been said in the way of illustration, as numerous examples are familiar to every one. It is possible that instinctive behaviour may have to be attributed to so lowly a group of organisms as the flat worms. Instinct reaches its greatest development among the insects, and some examples have been given above of the amazingly intricate series of actions which are performed by insects, under the guidance of instinct. There have been two lines of mental evolution among animals, one culminating in the insects and the other in the Vertebrates. Among the former instincts have become very specialized; among the latter they have remained far more generalized. Among the latter again there has been a far higher development of intelligence than among the former, thus further distinguishing the two lines of mental evolution. It is probable, however, that intelligence, though certainly at times in a very primitive form, always accompanies instinct, and to the discussion of intelligence we must now turn.
8. We saw how as lowly an animal as an Infusorian can in a sense learn from experience. It is only when learning from experience reaches a more advanced stage that we speak of intelligent action. If we watch one of the higher animals which, under the influence of desire, is striving to satisfy this desire, we find that it behaves in the following manner. An animal, for instance, is shut up in a box with food outside. It is led by instinct to all kinds of sporadic activities; it will clutch and claw and make every kind of effort to extricate itself. If some simple catch has been contrived which opens the door and offers a way of escape, the animal will probably sooner or later accidentally operate the catch and escape. If the animal is replaced in the box many times, it is found to escape on the average sooner. It learns in fact in some degree to operate the catch and thus to gain freedom and food. The question which arises is what degree of mental development we have to assume in order to account for these facts.
The stage in learning from experience which follows next upon that present among some protozoa is exemplified by the chick which at first instinctively pecks at various objects. If it pecks at a yellow caterpillar with an unpleasant taste it will drop it. The next time, or after a series of such experiences, it will avoid the caterpillar. The explanation seems to be that a modified response arises directly from the sight of the caterpillar. The sense-impression has become charged with feeling that first arose as the result of experience. This simple explanation is to be preferred to that which would assume the realization by the chick of the relation between the position when it again finds itself with a yellow caterpillar before it and the nastiness which it previously experienced. The process is thus one of the revival of acquired meaning, and we have now to ask if a higher stage of mental process is ever to be attributed to animals or whether the behaviour of the animal in the cage is to be explained on the same lines as the behaviour of the chick.
‘Let us suppose’, says Professor Hobhouse, ‘revival to operate in a mind capable of perceiving three objects A B C in definite space and time relations, C being something desirable, e. g. food. If the three objects are present to the senses, the first two leading up to the third (e. g. as intervening objects in space), conation will be definitely directed to C via A and B. Let this have happened and then let A alone be given. If the animal is hungry, i.e. if there is a conational basis to go upon, A will, according to the law of revival, excite a conation corresponding to the previous one, but this was a conation definitely directed to B and C in succession as things standing in a definite relation to A. The animal then directs its efforts to a point where, in accordance with the first experience, B and C should be. It looks for them, or if B is some change which brings C about, sets itself to perform B and so obtain C. Its action is directed to something not given, and this appears to be the germ of a conation or practical idea.’[87] It is thus possible that in the behaviour of the animal in the box we may have to recognize the first step towards a higher mental process. Effort may be directed to something not given and thus there may be the first sign of the emergence of an idea. Whether this is so or not, such an idea is certainly not a general idea; it is merely a reference to something to come, and that is all. This is the highest degree of mental development that we can attribute to animals and it may be noticed that, this being so, there can probably be no true memory among animals. Explicit ideas, therefore, among animals, so far as they exist at all, do not give rise to other ideas following one another in sequence. They are isolated and serve merely to guide action.
9. The highest form of mental process attributable to animals reaches a fuller development among men. This stage of mental development has been called the stage of perceptual correlation. How far the apprehensions of direct relationships in consciousness are developed among animals is doubtful; there is no doubt that among men such relations are apprehended. Action, therefore, is not merely connected indirectly with the result, as in the example of the chick; action is undertaken with an end in view. If the chick came to apprehend the relation between the caterpillar and the unpleasant taste, it would have reached the fully developed stage of perceptual correlation; we have seen that we have to assume in this case a simpler state of mental process, though in certain cases a study of animal behaviour does suggest some approach to the higher stage. At this stage, which is fully developed only in man, the world ceases to be presented merely as sense-impressions charged with feeling and takes the shape of a mass of objects of perception related together and underlying the sense-impressions and the feelings evoked by them.
In man there is developed a still higher stage of mental process which is his peculiar possession and chief distinguishing characteristic. This is the stage of conceptual thought. In the perceptual stage activity is guided solely by the presence of the objects perceived. If there is any anticipation of the end, the action from moment to moment is still always guided by what is actually given. In the conceptual stage action is guided by an ideal anticipation of the end. What underlies mental process at this stage is generalization. The situation as given is broken up and analysed; elements common to it and to previous situations are recognized and synthesized. These two processes of analysis and synthesis go on side by side and concepts are formed which are outside the world of perception. Common elements in the perceptual order are recognized and there is thus made possible a grasp of the continuity running through experience.
Man is thus no longer guided by what is immediately given in experience; he can make plans and shape his actions with an ideal end in view. With the development of conceptual thought goes the development of language, whereby man learns from others and passes on to others what is in his mind. Of the stage of conceptual thought there will be more to say in a later chapter. This further development is only mentioned here in order to contrast mental process in its highest form in man with the process in animals.
10. We have now to consider the bearing of mental development upon the process of reproduction. All animals are endowed with a certain power of reproduction which we shall call fecundity. Fecundity is measured by the number of ripe ova produced, the number of spermatozoa having no direct bearing on fecundity. We have seen that the highest animals—those most nearly related to man—are gifted with instinct and intelligence. The value of intelligence lies in the fact that it enables instinct to adapt itself to the special circumstances of the moment and thus to bring about its end more surely. The sexual instinct is in this manner assisted by intelligence, and among animals which copulate the power of reproduction is thus able to realize itself to the full or almost to the full. There may be certain failures to achieve reproduction and certain cases of perverted instinct; to some of these cases we have already referred. Broadly speaking, however, it is true that the highest development in animals of instinct and intelligence works towards the fulfilment of that degree of fecundity which is innately given. It follows, therefore, that in this sense mental development among animals has not in any fashion changed the position of the higher animals when compared with that of the lower animals. Reproduction in the sea-urchin and reproduction among the mammals—vastly as the mental processes differ—is still similar in this respect. The power of reproduction is realized to the full or almost to the full. All that instinct and intelligence do is to ensure that in this more complex process of fertilization the full power of reproduction is as nearly as possible realized—that is to say, that nearly all ova are fertilized.
Among men, even in the lowest stage in which they have been studied, the position is entirely different. Owing to the development of conceptual thought men act with some ideal object in view. Customs grow up which in their origin must be traced to some process of reasoning, however obscure, and action deliberately undertaken, as well as custom, may affect the realization of the power of reproduction. Thus among the lowest of primitive races we find that men abstain from intercourse for various motives which we must regard as due to the presence of reason. Or again, they may practise certain forms of mutilation of the sexual organs which may affect the power of reproduction. The origin of such a custom may be hidden; it may be almost certain that it was not originated with any understanding of its effect upon reproduction and even that its effect has never been recognized; nevertheless originally such a custom could only have arisen if reason was present. Similarly, among the lowest races there are abundant examples of the practices of abortion and infanticide which, though they do not affect fecundity, have an important bearing upon the quantitative aspect of the population problem and are again the products of reason.
Among men, therefore, owing to the development of a higher stage of mental power, fecundity is not realized to the full, and we have to distinguish between the power of reproduction, which we have called fecundity, and the actual degree of reproduction, which we shall call fertility. It may, perhaps, assist to emphasize what is meant if for a moment we think of the reproductive process among animals as ‘mechanical’. The introduction of this term should not be taken to have any ultimate significance—any reference whatever to the true nature of mental process. It is only used as a convenient term to illustrate the difference between reproduction among animals and among men. Among all species in a state of nature reproduction may be thought of as ‘mechanical’, whereas reproduction among men is never ‘mechanical’. The number of young produced in the case of the human species is far from being completely correlated with the fecundity. There may be all degrees of difference between fecundity and fertility. Among species in a state of nature fecundity and fertility are for all practical purposes one and the same thing because reproduction is ‘mechanical’ whatever may be the stage which mental development has reached. Further, such differences as exist among species in a state of nature between fecundity—the number of ripe ova—and fertility—the number of fertilized ova—are due to failures of the gametes to meet and may be called, just as the whole process may be called, ‘mechanical’. Such ‘mechanical’ differences between fecundity and fertility may also be found in man but the chief cause of the differences in the case of man is altogether of another kind and is due, as we have seen, directly to the development of conceptual thought.
It was said above that it was proposed to show that certain generalizations can be made regarding the process of reproduction among species in a state of nature. This then is the first generalization. (Fecundity and fertility are closely correlated and, compared with the position among men, reproduction may be thought of as ‘mechanical’ and even the failures to realize the full power of fecundity may be thought of as ‘mechanical’.)
11. It has been mentioned that fecundity is very large among all species in a state of nature and we have now to ask what it is that determines how large it shall be. As we have seen, the fecundity is roughly measured by the number of ova produced, and this number clearly depends upon many factors, such as the beginning and duration of the mature period, the number of eggs produced at any one time, and the length of the period between the epochs of egg production. Into details of the proximate causes of the differences in fecundity it is not necessary to go. What it is desired to know is what factor or factors in general ultimately determine the strength of fecundity in each species. We may first take some examples of the degree of fecundity drawn from various groups.
The common whelk lays its eggs in capsules of which a great number are produced. It has been calculated that a small clump of such capsules of about two cubic inches in size contains about 200,000 eggs. Another mollusc, Aplysia, may lay from 2,000,000 to 3,000,000 at a time. ‘An oyster may have sixty million eggs and the average American yield is sixteen millions.’[88] The number of eggs found attached to the edible crab in the breeding season varies between half a million and three millions. A single pair of flies may produce 20,000 larvae. The number of eggs produced by parasites may very largely exceed these numbers. Among the vertebrates the fish are the most prolific class. ‘In a Ling 61 inches long and weighing 54 pounds the ovaries contained 28,361,000 eggs; a cod of 21½ pounds 6,652,000. The least prolific of British food fishes is the herring, in which the number of ovarian eggs varied from 21,000 to 47,000 in four specimens examined.’[89]
These vast numbers of eggs produced at any one time make theoretically possible a prodigious rate of increase. It has been calculated that a single cholera bacillus can give rise to sixteen hundred trillion of bacilli in a day, forming a solid mass weighing a hundred tons. ‘Wallace quotes Kerner to the effect that a common British weed (_Sisymbrium sophia_) often has three-quarters of a million seeds; if all grew to maturity for only three years the whole of the land surface of the globe would not hold them. An annual plant with only two seeds would be represented by 1,048,576 in the twenty-first year.... If all the progeny of one oyster survived and multiplied, its great-great-grand-children would number thirty-six with thirty-three noughts after it, and the heap of the shells would be eight times the size of the world. Huxley calculated that if the descendants of a single green-fly all survived and multiplied they would, at the end of summer, weigh down the population of China. The common house-fly lays eggs in batches of 120 to 150 at a time, and may lay five or six of these batches during its life of about three weeks in very hot weather. At the end of summer, if all developed, and if there were six generations, the progeny of a single pair, pressed together into a solid mass, would occupy a space of something like a quarter of a million cubic feet, allowing 200,000 flies to a cubic foot.’[90] ‘There is no exception’, says Darwin, in a well-known passage, ‘to the rule that every organic being naturally increases at so high a rate, that, if not destroyed, the earth would soon be covered by the progeny of a single pair. Even slow-breeding man has doubled in twenty years, and at this rate in less than a thousand years there would literally not be standing room for his progeny. Linnaeus has calculated that if an annual plant produced only two seeds—and there is no plant so unproductive as this—and their seedlings next year produced two, and so on, then in twenty years there would be a million plants. The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when thirty years old, and goes on breeding until ninety years old, bringing forth six young in the interval, and surviving till 100 years old; if this be so, after a period of 740 to 750 years there would be nearly ninety million elephants alive, descended from the first pair.’[91]
12. These examples show that the power of fecundity, which is always huge, is in many instances much greater than in others. Were it not for the fact that normally all but a small proportion of eggs are always fertilized, it might be suggested that in those cases in which there was no copulation a much larger number of eggs was necessary than among the higher forms, in order that a sufficient number should be fertilized. This, however, can only be a partial explanation of the larger number of eggs among those lower forms where there is no copulation.
In order to obtain an answer to the question as to what it is which determines the fecundity of any species, it is necessary to look into certain features of the life of animals and plants in a state of nature. Observation and deduction bring one remarkable fact to light. The number of adults of any species at any one season of the year, when compared with the number in the corresponding period in other years, remains upon the whole constant. This fact cannot be based upon statistics, for we cannot take anything approaching to a census. Nevertheless, it is an unavoidable deduction from the known facts. The more emphasis that is laid upon variations in numbers from season to season, the more apparent does it become that such differences are trivial when compared with the possible rate of increase. But we know that all but a small proportion of eggs are fertilized, and as we date the existence of a new member of the species from the moment of fertilization, it is clear that the numbers composing every new generation greatly exceed the number of adults to which the new generation owes its existence. It follows, therefore, that all but a small proportion of the young of each generation perish before the adult stage is reached. The most remarkable increases in the adults of any species ever recorded are negligible compared with the possible increase, and observation shows that as a general rule there is no increase at all.
Fecundity is, therefore, in some manner connected with this fact that the great majority of fertilized eggs do not give rise to adults, and in order to throw further light upon this connexion we must ask how it is that the young perish.
13. To make clear how it is that the young of every species perish on so large a scale, it is necessary to refer to the interdependence of all living organisms. This can perhaps best be illustrated by reference to the chief distinction between animals and plants. A difference in the mode of nutrition is that which chiefly distinguishes animals from plants. There are other differences but their importance is small compared with that we may now describe. The need of food is common to all living things and is due to the nature of the living substance called protoplasm—the physical basis of all life. Protoplasm is of a very complex constitution. It is for ever wasting away and if life is to be preserved food must be supplied to compensate for the loss. The need is as great among plants as it is among animals, but the means of supplying it are fundamentally different.
Plants feed upon very simple substances—salts of nitric acid, salts of ammonia, and carbonic acid. Among green plants carbonic acid is taken in from the air through small apertures in the leaves known as stomata; the salts of nitric acid and ammonia are absorbed from solution in the water of the soil. Carbonic acid and water are synthesized within the cells of the plant into starch; starch is converted into sugar and the sugar is combined with the salts of nitric acid and ammonia to form amino-acids which are eventually transformed into proteids. Thus the plant makes good the unavoidable waste of its living substance by elaborating the highly complex protoplasm from the simplest elements.
The method pursued by animals is entirely different. They feed upon complicated substances, which may be divided into proteids, fats, and carbo-hydrates. These substances do not take their places directly in the living cells of the body; they first undergo a process of digestion, after which they are assimilated. Digestion involves the breaking down of these complex foods to a certain stage; proteids, for example, are reduced to amino-acids, and starches to sugars. In these forms they are soluble and are taken up by the walls of the alimentary canal and are afterwards resynthesized into proteids and starches.
The importance of this distinction lies in the fact that the only method of obtaining the highly complex substances necessary for animals is to feed upon the tissues of other animals or plants. It is obvious that every animal species cannot feed upon some other animal species; in the end animals as a whole must depend upon plants because plants alone are able to elaborate the substances which animals need. In a sense, therefore, animals are parasitic upon plants; in any case the existence of animals is bound up with the continued existence of plants. This interdependence of living organisms runs all through the conditions under which species in a state of nature live and takes a variety of shapes. The dependence of one organism upon another is largely connected with the question of the provision of appropriate surroundings which are often only found in the proximity of certain other species. Many species can only flourish in the neighbourhood of trees. The interdependence between certain species is very intimate. There are many examples of what is known as symbiosis, as when a certain species of sea anemone lives on the back of a particular species of crab. Again, parasites, which alternate between one host and another, are dependent upon finding a member of a particular species at a certain time in their life-history, as otherwise they perish. Many examples of interdependence are within common knowledge, and, bearing this feature of organic life in mind, we may go on to ask how it is that, through the elimination of a great proportion of the young of every species, the number of adults remains upon the whole constant.
14. Taking animals first, it is probable that the most common cause of elimination lies in the fact that the young of all species are consumed by members of other species. It is difficult to estimate even roughly the relative importance of the various causes of elimination; ‘the causes’, says Darwin, ‘which check the natural tendency of each species to increase are most obscure’.[92] The particular factor mentioned, however, certainly takes a very prominent place. The young of marine and fresh-water animals almost all form food for other species and are obviously exposed to attack. So too, though perhaps not to so great a degree, are the young of terrestrial animals; whether we think of the larvae of insects or the eggs of birds, we find that they are in most cases liable to be consumed by enemies. Even where copulation is internal, the developing embryo is, except among mammals, seldom long retained within the body of the mother, and once exposed to the outside world it almost invariably becomes an object of prey to many enemies. In fact, wherever we look, this cause of elimination plays a very great part, arising immediately from that aspect of the interdependence of species which is derived from the mode among animals of making up for the wastage of protoplasm.
Elimination again is largely due to failure to find those conditions under which alone life can continue. These conditions may be connected with the nature of the organic or of the inorganic surroundings. When the young of the flat worm, known as the Liver Fluke, which infects sheep and causes a serious disease, passes from the sheep to the exterior, it can only maintain itself for a certain time in the free-living form. Unless within this time it meets with a certain species of snail into which it penetrates, it will die. Besides such failures to find suitable organic surroundings, there may be failures to find suitable inorganic surroundings. The larvae of such species as the mussel, which require suitable surroundings to which to attach themselves in order that the adult form may develop, will perish if such surroundings are not available. There is a further class of factors connected with the inorganic surroundings which bring about elimination. They may be summed up under the heading of external circumstances. Variations in temperature, moisture and so on, when they pass beyond a certain limit, which is more or less clearly marked for each species, are followed by death. Under this heading comes also death from accident, as when animals perish from the violence of storms and in any similar fashion. It is of interest to note that starvation is seldom the primary cause of death. It may be a secondary result of abnormal external circumstances; extreme cold, though not affecting directly the members of one species, may be fatal to members of another species upon which the former feed. But when circumstances are normal, so far as observation goes, starvation is rare.
15. Among plants the same three groups of factors can be traced, though their relative importance is not the same as among animals. Elimination through consumption as food, for instance, by other species is not so important. To a large extent plants can serve as food for animals and survive. Nevertheless the young, especially in the form of seeds, are very subject to attack by animals; seeds are one of the principal forms of food for many animal species, and this form of elimination plays a large part among plants. Dependence upon suitable organic and inorganic surroundings plays much the same rôle as it does among animals. Some species can only flourish in the shade of trees and others in the open. Some species require one kind of soil and others another. The importance of external circumstances again is very similar.
There is another factor of a somewhat different nature which is of great importance. ‘With plants’, says Darwin, ‘there is a vast destruction of seeds, but, from some observations which I have made, it appears that the seedlings suffer most from germinating in ground already thickly stocked with other plants.’[93] In order that a seed may germinate, it must not only fall upon suitable soil but must find enough suitable soil unoccupied. Otherwise it will not germinate or will not develop into an adult. This is different from anything which happens among animals, and is clearly an approach to starvation. It is, however, better thought of as the result of the inability of any given area to support more than a given amount of life. The endowment of any area may be such as to render it incapable of supporting life at all, or it may be such as to render it capable of supporting any degree of life up to and beyond that for which there is space. In the sea the amount of nitrogen is the limiting factor, and the deficiency of nitrogen is such that the question of space does not arise.[94] In many parts of the world’s surface, however, the endowment is such that more plants could be supported than there is space for.
In this connexion it may be noted that the limitation of the surface of the earth is not a cause of elimination in the true sense. This is best seen if we imagine the surface to be extended. If to a continent already inhabited there is added an unoccupied area, there will, if the new area is generally of the same nature as that alone formerly existing, be a spreading of organic life over the new area. It will only be at the fringe of the occupied area that there will be any difference in the amount of elimination of plant life. Unless the occupied area is of very small extent, there will be no difference except within this narrow fringe. In the fringe there will be a lessening of elimination, other things being equal, because there will not be the same number of seeds which fail to grow into plants owing to the previous occupation of suitable soil, as in the more central parts of the area. When the new area has been entirely occupied, the same conditions as existed in the smaller area will exist throughout the larger area. Further, if the surface available for occupation were indefinite in extent, there would, except at the fringe, which would in this case be permanent, be no difference as regards the amount of elimination. All that has been said applies equally well if, instead of imagining these additions to take place after evolution had reached its present stage, we imagine evolution to have taken place from the beginning on an area of indefinite extent.
16. We have, therefore, some idea of the manner in which the young of animals and plants perish. Let us consider any animal species; we find that the young are faced with a large number of dangers. The new members of the species may be consumed by some enemy before they have developed beyond the stage of the fertilized egg or at any stage in their development. They may in general not meet with favourable organic and inorganic surroundings, or at some particular stage they may not meet with the environment necessary. At any time they may perish from unfavourable external circumstances. The position of young plants is similar, and in addition they may fail to find sufficient space in which to live.
The dangers which any species encounters remain both in kind and in degree fairly constant over a considerable period of time, and, unless in each generation a number of young survives at least equal to the number of adults in the generation to which it owes its birth, the species will decline. It follows that the power of reproduction must be such as to ensure that at least this number of young will survive. The power of reproduction in any species is therefore connected with the sum of all the dangers which the young of the species encounter. But it is not true that the greater the fecundity the better for the species. Reproduction over and above this degree would place the young in a less favourable position. Competition bringing no corresponding advantages would be increased, and starvation or injurious semi-starvation would result. Any considerable increase in the strength of fecundity beyond that which is essential could not therefore be beneficial.[95]
The facts regarding the conditions of life and the dangers to which the young of different species are exposed coincide with the view that the strength of reproduction is in the main determined by the sum of these dangers. The greater strength of fecundity among those species which shed their eggs into the water cannot be attributed, as we have seen, to any failure of fertilization on a large scale; it may be attributed, however, to the numerous dangers which the young of such species must encounter. The chance that any single fertilized egg will grow into an adult is far less in these cases than when the eggs are retained in the body of the mother and when the young are guarded by the parent, and, unless fecundity was on a large scale, a sufficient number would not survive. Among plants reproduction must always be on a large scale because it is necessary to ensure that a sufficient number of seeds will fall, not only on suitable ground, but on suitable ground that is not so occupied as to prevent growth to the adult stage, in addition to the necessity of providing such numbers as will ensure a sufficient number passing through all the other dangers. Eggs and young abandoned by the parents may be variously exposed to danger. The development of instincts common among insects which lead to the hiding of eggs in places where danger of destruction at the hand of enemies is decreased, and to the provision of food for the young when they develop from the eggs, is accompanied by a decrease in fecundity. Further developments of the parental instinct are accompanied by decreases in fecundity as the degree of danger lessens. Parental care for the young is not uncommon among the invertebrates. There are a number of cases in which the young are retained in brood-pouches, as for instance by the common water-flea. The fresh-water leech, Clepsine, broods over its young. Among the vertebrates the fish for the most part take no care of their young. Some fish, however, such as Gasterosteus, the Stickleback, make nests. No great advance is found among the Amphibia or among the reptiles. One reptilian group, however, the Chelonia, shows a remarkable advance; they live in pairs and guard their young with care. If marriage be defined as ‘a more or less durable connexion between male and female lasting beyond the mere act of propagation till after the birth of the offspring’,[96] then the beginning of marriage is discernable in this group. This more or less durable connexion between male and female is a well-known characteristic of birds, as is also care for the young. ‘Most birds when they pair do so for good and all until one or the other dies.’[97] The connexion is not so durable, and the parental instinct is not so highly developed, among mammals as among birds. The retention of the young within the body of the mammalian mother, however, greatly decreases the dangers to which the young are exposed. It is also worthy of note that those species both of birds and mammals which prey upon others are on the whole less fecund than other species, a fact which is to be connected with the lower degree of danger to which their offspring are exposed.
The lower degree of danger to which the young are exposed, the less the fecundity; and the less the fecundity, provided that it reaches the strength necessary to preserve the species, the better on the whole for the species. In this manner we reach the second generalization regarding the quantitative aspect of the population problem among species in a state of nature, which may be stated by saying that the strength of fecundity in any species is determined by the sum of all the dangers to which the young of that species are exposed. This must be qualified, in so far as fecundity and fertility are not the same, by adding to the dangers to which the young are exposed the danger that a certain proportion of eggs will not be fertilized. It follows that among men, since fecundity and fertility are not the same for quite other than ‘mechanical’ reasons, fecundity is not directly related to the dangers to which the young are exposed. It is clear that, when men, as is now the case on a large scale, both abstain from intercourse and interfere with the natural result of intercourse, and at the same time increase in number, the strength of fecundity is considerably greater than that which would enable a sufficient number of young to escape the unavoidable dangers. But the ancestors of man must once have been subject to the same conditions as those to which species in a state of nature are now subject, and it will be into the causes and results of this progressive divergence from the former conditions that we shall look in the first part of this book.
III THE BASIS OF THE POPULATION PROBLEM: (2) THE QUALITATIVE ASPECT
1. We have now to consider the qualitative aspect of the population problem. There are two questions to which an answer is required. First we ask: What is the nature of the changes which occur? In other words, if we may speak of history among animals and plants, we want to know what kind of changes underlie the facts which go to make up that history. The second question is: How have these changes come about? There is no doubt about the answer to the first question, and it can be given very shortly. Though there is a certain consensus of agreement regarding the answer to the second question, there are considerable differences, of opinion over points which are not unimportant, and in order to deal adequately with these points a long discussion would be required for which there is no space. All that can be done here is to set out the most important facts; they will provide a satisfactory answer to the first question and enable some indication to be given of the lines which the answer to the second must follow.
However slight the treatment of the problem, it must begin with a reference to the physical basis of inheritance. Some description has been given of the process of fertilization. It was said that only the head and middle-piece of the spermatozoon penetrate the egg, and that no cytoplasm or ordinary granular protoplasm can be demonstrated in these parts of the spermatozoon. The head is the nucleus of the cell, while the middle-piece contains the centrosome, a body which is attached to the nucleus and plays an important part when the nucleus divides. From these facts a very important conclusion follows. It is known that both parents contribute equally to the offspring; therefore as the male parent contributes only a nucleus and its appanage the centrosome, the basis of the inherited qualities must be sought in the nucleus.
Attention is thus directed to the nucleus, which can sometimes be seen in the living cell. Its detailed structure can, however, only be made out in specimens which have been preserved and stained. The nucleus is then seen to consist of a thin wall within which is contained a colourless sap. In the sap are a number of beads of a darkly staining substance known as chromatin suspended on delicate threads of a substance known as linin. The division of a cell is always preceded by the division of the nucleus and, when the nucleus divides, the chromatin undergoes certain remarkable changes. The beads of chromatin become aggregated together into rods—the number of rods which appear being invariably constant in the same species, though varying from species to species. These rods are known as chromosomes. Beyond saying that the rods divide into two and that each daughter nucleus, and therefore each daughter cell, is provided with that number of chromosomes which is typical for the species, it is not necessary to follow the details of the process of division any farther. Stated in the briefest possible form, this is what happens during ordinary cell-division, such as that which takes place when a fertilized egg is growing from a single cell into a multicellular adult.
There is one remarkable exception to this type of nuclear division. In the last division but one of those series of divisions which lead to the formation of both male and female gametes, half, and not the full number of chromosomes, is transmitted to each daughter nucleus. If therefore the typical number of chromosomes in the nucleus of one species is eight and in another four, the number of chromosomes in the gametes will be four and two respectively. In the former species the nucleus of the egg will have four chromosomes, and that of the spermatozoon also four, and the full number typical of the species will only be restored when the nucleus of the spermatozoon fuses with the nucleus of the egg in fertilization.
The invariable reappearance of the same number of chromosomes in ordinary cell-division, their reduction to half that number in the last division but one which precedes the formation of the gametes, the complicated mechanism which is employed and other evidence all lead to the conclusion that the location of the basis of the hereditary qualities can be further narrowed and sought in the chromatin—in one element, that is to say, of the nucleus.[98]
2. The nucleus must not be thought of as isolated from the rest of the cell; there is a constant and active interchange between the nucleus and the cytoplasm. It has actually been demonstrated that at times particles stream out from the nucleus into the cytoplasm. The nucleus is the centre of activity; without the nucleus the cell cannot live. This being so, how are we to view the process of development from the fertilized egg to the adult? The process can be studied in detail. The egg divides into two cells, then into four, eight, sixteen, thirty-two cells, and so on. The gradual differentiation of the organs can be watched and their lineage to certain cells in earlier stages traced. At every stage the developing organism comes under the influence of certain stimuli provided by the surrounding conditions. Very many elements in the environment act as stimuli; among them are light, temperature, gravitation, food, and so on. Provided that the environment is normal, provided, that is to say, that the variations in the stimuli do not exceed certain limits, an adult member of the species will be formed. What is implied in the term ‘normal environment’ will be more fully discussed in Chapter XIV, where the results of subjection to an abnormal environment will also be studied. That a large number of stimuli varying within only narrow limits are necessary, will there also be shown to have been proved.
The process of development, therefore, takes the shape of the growth of a particular organic form through the play of certain stimuli upon the germinal constitution. The germinal constitution has, as we have seen, apparently to be identified with the constitution of the chromosomes of the fertilized egg, of which half are derived from the father and half from the mother. It is known that the characters, which the organism exhibits, in some manner have a basis in the germinal constitution. The number of these separate characters is very large. What view then are we to take of the nature of the germinal constitution? In the first place every character as seen in the organism is the result of the play of certain stimuli upon something in the germinal constitution. This something can only be thought of as predispositions to the development of certain characters under certain stimuli and to the development of characters differing in degree or in kind from the former characters under other stimuli. It is altogether misleading to speak of anything but predispositions as present in the germinal constitution, though, of course, for the sake of brevity other phraseology may be employed once this point is understood. When, therefore, we speak of the inheritance of any character, we mean that there is a predisposition in the germinal constitutions both of the parent and of the offspring to develop this character under certain stimuli, which stimuli must play both upon the parent and upon the offspring if the character is to be manifested in both of them.
If we have to regard the germinal constitution as somehow containing very many separate predispositions or, as they are often called, factors, is it in the second place possible to say in what these factors consist? No definite answer to this question can as yet be given. Certain hypotheses have been put forward. Weismann, for instance, suggested that the factors were to be sought in groups of molecules of chromatin. It is not necessary, however, to postulate definite and separate particles as the physical basis of the predispositions. The protoplasmic molecule is a very complex structure consisting of a very large number of atoms. Similar atoms may be differently grouped within a molecule, and different predispositions may well be functions of different groupings.
3. In order that we may answer the first of the two problems set out at the beginning of the chapter we must consider in rather more detail in what the development of an organism consists.[99] Every character is, as we have seen, the result of the influence of the environment upon what is innately given. If two individuals were endowed with precisely similar germinal constitutions, and if precisely similar stimuli played upon each of them, then the adult forms would be similar in respect of all their characters. But if the stimuli are not similar, if, for instance, more food is provided in one case than in another, then, though the germinal constitutions are similar, one adult may be larger than the other. Again, let us suppose that the germinal constitutions differ, that, for instance, there is in one case a predisposition to the development of greater size than in the other, then, even if the stimuli are similar, the adult forms will differ. The larger members of each of these pairs may thus resemble one another very closely in outward characters; but this close resemblance will not be due to similar germinal constitutions. It follows that by mere outward inspection no conclusion can be reached as to the germinal constitution. There are, therefore, two classes of influences at work, and alterations in either class of influence will bring about alterations in the resulting organism; similar characters may be the product of one kind of predisposition and one kind of stimulus, or of a different predisposition and a different stimulus. It also follows that we cannot speak of certain characters as inherited and of others as acquired. Let us suppose that some departure from the normal structure occurs. It may be due to a change in the environment, that is to say, to a new stimulus acting upon an unchanged germinal constitution, or it may be due to a change in the germinal constitution when no change in the environment takes place. It should not be said that in the former case the new departure is acquired and in the latter case that it is inherited. What has happened is that in the former case a new stimulus acting upon the old factors has brought forth a new character, and in the latter case that the old stimulus has brought forth a new character because it has acted upon a different factor.
Though the popular distinction between characters which are acquired and characters which are inherited is misleading, there are, nevertheless, two kinds of variation. A new departure may be due to a change in the germinal constitution. In this case the new character will reappear in future generations, provided that the changed germinal constitution remains and provided that the complex of stimuli which composed the environment does not change. Such a variation may be called a ‘mutation’. A new departure may also be due to a new stimulus acting upon an unchanged germinal constitution. In this case the new character will only reappear in future generations provided that the new stimulus remains. Such a variation may be called a ‘modification’. Mutations, therefore, are transmitted in the germinal constitution, while modifications are not so transmitted.
4. Already we have reached the answer to the first problem. Permanent change in organic form is due to germinal change. But before we go on and ask how germinal changes, that have arisen, become established, we must consider further the difficult problem of the manner in which germinal changes arise. A reference first to what are known as ‘pure line’ investigations and afterwards to Mendelian phenomena will illustrate what is known as to the nature of existing germinal differences; for until we have some such information, we cannot profitably ask how existing germinal differences arise. The best known ‘pure line’ experiments are those carried out by Johannsen with beans. The flowers of beans fertilize themselves; the offspring, therefore, have approximately the same germinal constitution. The offspring constitute a ‘pure line’, for by a ‘pure line’ is meant a group of children which are the offspring of a single parent. The character selected for investigation was weight and it was found that, if beans were collected from a bean-field and weighed, every gradation occurred between a minimum of about 20 centigrams and a maximum of about 90 centigrams. When the beans were separated into three classes—heavy, medium, and light—sown and plants raised from them, the average weight of the beans produced by the plants derived from the heavier seed was greater, though not proportionately greater, than the mean weight of all the beans, and that the average weight produced by the plants derived from the lighter seed was less, though not proportionately less, than the mean weight of all the beans. There was, in fact, a certain regression on the part of the heavy and light classes to the mean weight. A similar tendency to regression to the mean can be observed when other characters are similarly studied. The average stature, for example, of the offspring of tall parents is slightly nearer the mean stature of the race than the average stature of the parents.
This tendency to regression to the mean has long been known, but it was not until Johannsen proceeded farther and investigated inheritance within a ‘pure line’ that it was understood. In the experiment described, no attention was paid to the ‘pure line’. When Johannsen separated the beans produced by the self-fertilization of a single plant, divided them into heavier, medium, and lighter classes, sowed them and weighed their progeny, he discovered a very interesting fact. The average weight of the progeny of a heavy bean and of a light bean belonging to the same ‘pure line’ was the same. The conclusion to be drawn from this result is that the differences in weight between the offspring of a single self-fertilized plant are due to differences in the stimuli which play upon them. Obviously the stimuli do differ; the weight is affected by differences in light, shade, number, and position of the beans in a pod and so on. But since the offspring of a single plant have approximately the same germinal constitution, the average weight of the offspring of light beans, which are light because of subjection to less favourable stimuli than the average, will not be on that account lighter than the mean weight of the strain, and similarly _mutatis mutandis_ with regard to the offspring of the heavy beans.
It follows, therefore, with regard to this particular character that there are a number of different strains in the population. The beans arising from any one strain are not of the same weight because they have been subjected to different stimuli. If each strain was pure and if differences in environmental stimuli could be removed, then beans gathered from a bean-field would not exhibit a simple gradation in weight: there would be a number of steps and as many steps as there were strains. In actual fact, the modifications produce the gradation which is observed. The fact that the nature of the germinal constitution cannot, as stated above, be determined by a mere inspection of the characters is exemplified by this experiment. If we take a bean weighing, say, 55 centigrams, it may belong to a strain which varies, say, between 20 and 65 centigrams, or to a strain which varies between 40 and 90 centigrams. It is only when this bean is sown, and the weight of the offspring calculated, that the strain to which it belongs can be ascertained. The experiment further shows why regression towards the mean is observed, when, instead of limiting investigation to a ‘pure line’, beans differing in a certain respect from the average, by, for instance, greater weight, are selected and sown. Such beans will belong to several different strains; they will, however, include more which have been favourably than unfavourably influenced by the surroundings. The average of the weight of all their offspring will therefore be less than the average weight of the parents. At this point we touch upon the problem of selection, but before we go on to deal with this question, it is necessary to say something more about variation and the origin of variations.
5. Self-fertilization is very exceptional, and what happens in the case of the beans, though illuminating, is not typical. As a general rule in reproduction, two parents contribute to the germinal constitution of the offspring. Strains, therefore, do not remain pure, as in the case of the bean, because they are continually crossed; we require to know what happens when crossing takes place. This study, first successfully undertaken by Mendel, has been greatly extended in late years. We may first illustrate in the simplest form what it was that Mendel discovered and then go on to inquire what deductions bearing upon the question we have to answer are to be drawn from it.
A large number of experiments of the following kind has been made. Two strains in any species are chosen; these strains exhibit opposed characters. Such characters may be tallness and dwarfness, colour of the flower, shape of the comb in fowls, condition of the seed, whether smooth or wrinkled, and so on. We may call one character A and the other _a_. The two strains are crossed, and in the first generation the offspring are all alike and exhibit a character, A′. This character may be the same as either A or _a_, a blend between them or something wholly new. Whatever form it may take, it is produced by the interaction of A and _a_. The members of this first generation are then interbred, and of the second generation one quarter exhibit the character A, one quarter the character _a_, and the remaining half the character A′. If the quarter exhibiting the character A are interbred, all the offspring exhibit the character A, and the same holds good regarding the quarter exhibiting the character _a_; but if the half exhibiting A′ are interbred, the offspring will split up in the same proportion as in the previous generation, one quarter exhibiting A, one quarter _a_, and one-half A′. This result holds good for any number of generations so long as interbreeding is continued.
Into the very numerous complications which occur it is not necessary to go. They are all interpreted by extensions of the simple explanation which is applied in the elementary case given above. It is supposed that all characters which behave on crossing as above are represented in the germinal constitution by factors which behave as separate units; such characters are called ‘unit-characters’, and such factors ‘unit-factors’. It is further supposed that each gamete bears one unit-factor only in respect of each unit-character. If the strain is pure, as in the case of the two strains exhibiting characters A and _a_, then all the gametes will bear the unit-factors for A and _a_ respectively, and the fertilized eggs resulting from the crosses between them will therefore contain both unit-factors. The hybrids, which, as we have seen, exhibit the character A′, will produce gametes, half of which bear the unit-factor for A and half the unit-factor for _a_. When the hybrids interbreed, on the average of chances one quarter of the fertilized eggs will have two factors for A, one quarter two factors for _a_, and one-half both a factor for A′ and a factor for _a_. In this manner the splitting up of the second generation is explained.
What is important in this explanation is the conception of unit-factors. The extension of the explanation to cover the more complicated cases does not involve any modification of principle. It follows that the germinal constitution contains a very large number of unit-factors; what therefore is innately given in the germinal constitution is a collection of such unit-factors. Each unit-character based upon a unit-factor can theoretically be separately distinguished and isolated. The complications to which references have been made are in part due to the difficulty of distinguishing unit-characters. What is apparently a simple character may not be a unit-character, but a combination of unit-characters. This apparently simple character cannot appear unless all the unit-factors, upon which these unit-characters are based, are present in the germinal constitution.
It may next be asked whether all unit-factors behave in this manner when crossed. To this no definite answer can yet be given. The successful analysis of apparently contradictory cases and the continual discovery of characters which do behave in this fashion seem to point to an affirmative answer. The suggestion is that, when this mode of behaviour cannot be demonstrated, it is because the unit-characters have not yet been distinguished and isolated.
This brief reference to ‘pure line’ investigations and to the Mendelian analysis of crossing leads therefore to the following conclusions. When, as in the case of the self-fertilizing bean, the strains are kept pure, existing germinal differences in respect of any character are found to be of the nature of steps which are usually small—though in outward manifestation the differences are smoothed over by the influence of environmental stimuli. This is the nature of the germinal differences, and they remain what they are—apart from the origin of new factors or of the loss of old factors, and apart from the effects of a differential death-rate. When, as is usually the case, biparental reproduction takes place, the position is more complicated: strains are being continually crossed, and, as the result of the chance mixture of factors in the germinal constitution of the children, the offspring of the same parents differ in their germinal constitution one from the other. Therefore, in any species in which biparental reproduction takes place, new combinations are constantly arising; but, though in this manner the germinal constitution may in a sense change, the change is due simply to a shuffling of factors. What we require now to ask is what is known as regards the manner in which new factors arise and are added to the germinal constitution, and the manner in which old factors drop out and are lost from the germinal constitution; for it is only owing to such additions and to such losses that true germinal change occurs, and that shuffling is rendered possible.
6. The interpretation of the results of the crossing of different strains has shown what kind of changes underlie the appearance of certain mutations. It has been shown that many of the varieties of domesticated species have originated by the apparent loss of one or more unit-factors.[100] Thus the numerous varieties of domestic rabbits and of sweet-peas are all descended from a single wild species of rabbit and of pea, and differ from the wild stock not by an addition to, but by an apparent subtraction from, the total number of factors in the germinal composition of the wild stock. The reasoning which has led to this conclusion need not be followed here; one proof is that when certain varieties are crossed, characters of the original stock reappear, due to the fact that, one variety having apparently lost one factor and the other another, crossing results in the re-combination of the factors necessary to the manifestation of the original character.
This is a strange conclusion, but it seems nevertheless to be true that in this manner many domestic varieties have arisen. If this was the only manner in which mutations could come about, then we should be driven to imagine that the most elementary form of life contained within it innumerable factors, and that evolution has merely consisted in the apparent dropping out of factors. This conclusion has indeed been tentatively suggested. But until it has been definitely shown that this is the only manner in which mutations originate, it must be supposed that changes in and additions to the complex of factors can and do occur. And we may note that certain distinguishing characters of domestic varieties of fowls and of pigeons appear to have arisen by the addition of factors; thus the ‘single comb’ of fowls is the original character of the wild stock which has been modified by the apparent addition of other factors and not by the dropping out of one or more existing factors. It is again not necessary to go into the reasons which have led to this conclusion. The conclusion is a deduction from the analysis of crosses between different breeds of fowls.
7. For the most part we are quite ignorant as to the causes which have led to the apparent losses and apparent additions of factors, though a few observations seem to indicate certain circumstances under which the dropping out of factors may take place. In this connexion some reference must be made to the problem as to the inheritance of acquired characters, though it follows from what has been said above regarding terminology, that we should more correctly speak of this problem as the question whether modifications in any one direction tend to be followed by mutations in the same direction. As the result of prolonged discussion and controversy it is now generally held that nothing of the kind takes place. It is almost universally agreed, for instance, that such modifications as are induced among men at the present day do not lead to mutations in the same direction. Therefore we may for the purposes of this book, so far as man is concerned, take it that acquired characters are not inherited. But looking at the problem as a whole it cannot be regarded as settled. There is, for example, some evidence of the parallel induction of modifications and of mutations; but the question may be raised whether such cases if substantiated fall under the heading of the inheritance of acquired characters. Again, some biologists regarding the problems of evolution generally find difficulty in arriving at an explanation unless under certain circumstances adaptive variations are followed by mutations.
We are thus left with the fact that mutations arise, and may be either large or small. Outwardly, variations in characters are usually continuous, because the environmental stimuli vary continuously, smooth over and obscure the differences due to mutation, as in the case of the beans mentioned above. But, discounting the influence of the environment, the mutations themselves may form a series separated by steps that are so small as to be scarcely measurable or which may be very large. The weight of the beans is an example of the former kind of mutation; the so-called ‘meristic’ variations, when another member is added to a series, the addition, for instance, of a vertebra to the vertebral column, is an example of the latter kind.
Whenever a mutation occurs, we have to think of it as founded upon some change in the germinal constitution. Such changes are of the nature of modifications of factors—and may be positive (leading to the apparent addition of factors), negative (leading to the apparent loss of factors), or qualitative. But of the nature of these changes we know little, and of their causes less. What is important, however, is that these changes do occur. Further, they occur in all directions. The direction is, of course, in a sense determined by the starting-point—by what is already given in the germinal constitution—but, given the starting-point, mutations apparently occur in all directions. It is a matter of importance to know whether mutations ever tend to occur more in one direction than in another. Nothing definite has been ascertained as to this particular problem, though, as we shall note later, certain facts with regard to the evolution of animals suggest that there have been tendencies to change along certain lines. It may also be asked whether the continued selection of a character in any way affects the direction of the variation of the germinal constitution. To this again there is as yet no definite answer. On the whole it is not probable that selection has any such effect.
8. So far, therefore, as we have at present gone, we have found that permanent change is of the nature of germinal change. We have also discussed the nature of germinal differences as they exist between different individuals, and we have discussed the nature and causes of germinal change. With regard to variation there is much which is doubtful and obscure, but bearing in mind the essential features of what is certainly known, we may turn to consider what passes in the organic world. Upon this subject there is much less uncertainty. We have seen how huge is fecundity. Of the young in any generation, only about that number survives which equals the number of adults in the generation from which they are derived. For normally in the organic world the total number of adults of any species at corresponding periods in succeeding years remains much the same. The instances of a marked increase in the number of any species are rare, and are usually traceable to the intervention of man, as the result of which certain of the dangers which normally confront the young have been removed. It follows, therefore, that normally of the many thousands of fertilized eggs of a fish, for example, all but two perish. Even when the most rapid increase ever observed is taking place, the great majority of young perish. From a consideration of the circumstances it is evident that upon the whole those individuals which present certain characters will have a better chance of surviving than others which do not present these characters.
This point demands further consideration, because upon it turns the whole question of natural selection. What is involved in this theory is that the death-rate is selective, that those individuals which are best adapted to the surroundings which confront the species do, on the whole, have a better chance of survival. It is adaptation which determines fitness, but the concept of adaptation does not of necessity include any idea of progress. Given any complex of surroundings such as that which confronts any species, there may be a more or less close fitting of the organisms to this complex. The closeness of this fitting may have been obtained by a simplification of structure, a complication of structure, or it may be that for long ages the closeness of the fitting has been attained by the elimination of departures from the mean of the species in any direction and the preservation of the average type.
In this connexion it has often been pointed out that the death-rate in certain cases is not selective, and does not therefore involve the survival of the more fit and the elimination of the less fit. When the whale opens its mouth and engulfs vast numbers of small organisms upon which it feeds, there is apparently no escaping of certain types of these organisms accompanied by a greater elimination of other types. But these cases are not on the whole common, and further there is nothing in such cases which counteracts selection; it merely means that sometimes selection is not operative. A consideration of the mode of operation of the factors of elimination, the general nature of which has been indicated, leads without any doubt to the conclusion that in the vast majority of cases, when any organism meets its death, either that organism does not possess some character which other organisms possess and which have enabled them to survive, or it possesses some character which other organisms do not possess, and which at some crucial moment has told against it. This subject could be considered at great length, but it must suffice to say here that the more experienced naturalists are, and the greater the knowledge they have of the conditions of organic life, the more it is borne in upon them that the death-rate is upon the whole selective, and that the best adapted types have a better chance of survival than other types.
From the nature of the case it must be difficult to obtain statistical evidence of natural selection. There are, however, certain cases known which are of great interest. Bumpus, for instance, after a storm in America collected 136 sparrows, all of which had been injured. Of these 72 recovered, while the remainder died. He weighed and measured all the specimens and compared the figures for the survivors with the figures for those which had perished. It was found that the average type of the latter was larger and heavier than the average type of the former. It was also observed that there was a less wide range of variability among the survivors than among the dead, showing that the favoured type approximated more closely than the others to the average type of the species. This favouring of the average type has been shown to occur by other observations, and it may be supposed that normally it is the average type of any species which is best fitted to the particular niche in nature occupied by the species, and that therefore adaptation will be measured by the nearness of approach to this type. When, on the other hand, circumstances are changing, some deviation from the average type will be favoured.
9. This leads us to ask in more detail what it is that happens in the process of selection. Selection has been likened in its action to a sieve separating the fit from the unfit. But fitness is measured by the characters exhibited, and these characters may be either of the nature of mutations or of modifications. What is exhibited is selected quite apart from the underlying nature of the character; but it is only when variations of the nature of mutations are selected that there results any change in the composition of the germinal constitution of the species. So far as selection is merely that of modifications within a strain, there will be no change in the average germinal constitution of the progeny. It is only in so far as selection is a selection of strains that there will be any change. If the strains among the beans referred to above can be isolated, then the strain with the predisposition towards the greatest weight can be isolated, the other strains eliminated, and the average weight brought up to that found in this strain. If the strains cannot be isolated, then an approximation only to this result can be made by the continued selection of strains of the greatest weight, and this is what occurs in nature.
This leads to the most important conclusion of all. Selection can only act upon what is given. We may put aside the possible but quite unproved influence of selection upon the direction of mutation. Apart from this, selection can have no other effect than to eliminate certain strains and to favour others. Supposing that under changing circumstances a certain character is favoured, all that can happen through selection is that the strain exhibiting this character will be favoured and all other strains gradually eliminated. Further than this change cannot proceed until mutations have occurred in the direction of further increase in this character. As has been said, selection is no more than a sieve; as a rule it is occupied in separating out the extreme types and favouring the mean, but at times under certain circumstances it will favour some type that deviates from the mean, but it can do no more than favour what types are at any given moment in existence.[101]
10. We set out to answer two questions regarding quality. We asked in what change among species in a state of nature consisted. The answer to this is clear; it consists in changes in the germinal constitution. If we can speak of history in connexion with species in a state of nature, then their history is based solely upon germinal change. We also asked how change came about. It is less easy to answer in a few words. Obscure as are many of the details connected with the process, there is a sufficient measure of agreement regarding the main facts to enable an answer shortly to be formulated. The answer rests upon two series of facts. The observed characters of organisms are based upon certain predispositions in the germinal constitution. These predispositions or factors under the stimuli of the environment give rise to the various characters. These factors are derived from both parents through the fusion of the gametes, and the complex of factors in the offspring is the result of a chance mixture of factors. There may further at times be a dropping out, an addition to, and perhaps a modification of the factors. Secondly, the death-rate is selective. Although the result of selection is confused by the effect of modifications which smooth over the differences due to differences in the germinal constitution, the effect is that individuals with certain factors are favoured and others with different factors are eliminated. Therefore the average nature of the factors may be changed should any type, other than that approximating to the normal type, be favoured.
It is possible in this manner to understand how change has come about. There are many difficulties, but they are all capable of fairly satisfactory explanation. None at least is insuperable. There is one problem which is perhaps somewhat difficult to solve unless a particular supposition is introduced. This problem is connected with the evolution of organs along certain lines, as, for instance, the evolution of horns and teeth in the vertebrates. This class of evidence has chiefly impressed itself upon palaeontologists, and one of the most distinguished of them has stated that from this class of evidence he concludes that ‘there are fundamental predispositions to vary in certain directions’.[102] This is the supposition which it may be necessary to introduce, but which does not in any way conflict with what has been said.
IV THE POPULATION PROBLEM AMONG MEN
1. It has been shown in the last two chapters in what the population problem among species in a state of nature consists. With regard to the quantitative aspect in particular it has been shown that among such species mental evolution, greatly as the stage reached differs between the lowest and the highest forms, has not attained a point at which the essential features of the position have in consequence been affected. Enough has been said to show that in the case of the most primitive races of man now living mental evolution has reached a point in consequence of which the quantitative problem has assumed a totally different aspect.
With regard to the qualitative problem the question also arises as to how far mental evolution in man has affected the position. In one very important respect mental evolution has wholly altered the position of man as regards this aspect of the problem, as it has regarding the quantitative aspect. How this has come about may be considered after it has been observed that mental evolution has also been the cause of other changes which, while they do not alter the fundamental position of man as regards the qualitative aspect, yet are of great importance.
As we have seen among species in a state of nature change is founded upon germinal change. So, too, among men there is germinal change, and so far as history (using the term in the widest sense to include what is often rather meaninglessly called ‘pre-history’) is connected with germinal change, so far it is of essentially the same nature as change among other species. But both the direction and intensity of germinal change among men have been greatly influenced by mental evolution. Certain causes of elimination have been removed wholly or in part, others have been introduced. The facts are familiar; there is no need to labour the point. It is also worth noting that, should it be found that mutation frequently arises owing to alterations in the environment during the formation of the germ-cells, such a discovery might have considerable bearing upon the position in man. Owing to human activity under the guidance of reason, the environment has been profoundly changed in many directions, and without question in consequence of such changes the germ-cells of human beings are subject during their development to far more varied stimuli than are those of other species. This, however, is only a possibility. Nothing is known with certainty upon the subject. It may be that the great variety of foods, the absorption of alcohol and nicotine, the various occupations and customs, and many other factors, all ultimately traceable to reason, may, some of them in some way, tend to bring about mutation in man.
It is by making possible the development of tradition that the evolution of reason has fundamentally changed the nature of the qualitative problem among men. Into the nature and origin of tradition it will be necessary to go in another chapter. Here all that is required is an indication of its main features in order that its connexion with the problem of change may be understood. In the stage of conceptual thought reached by man, the formation of free ideas is the outstanding feature. With the development of conceptual thought went the development of language. By language ideas can be passed from one man to another and also from one generation to another. There are other ways in which the results of reasoning can be handed on, but they need not be considered at present. What is important is that they can be and are handed on. Let us consider for a moment the question of skill. Some improvement may be made in the methods of hunting or of fishing. It may, of course, be lost, but it may be, and perhaps usually is, transmitted to other men by the inventor and afterwards to succeeding generations. Tradition is, in fact, cumulative. Even among the most primitive races now existing there is a huge mass of tradition. Succeeding generations do not necessarily start at the beginning again. They start with the experience of the race behind them, so far as it has been preserved.
Among the higher animals there is a certain handing on of what has been learnt by experience; to this extent there is tradition also among them. We shall return to this point later. So relatively unimportant, however, is tradition among other animals, that we may for the moment regard tradition as something which is found among men only. It is clear that tradition has played some part in any case in producing the changes which we call history. We have only to think of the rise of Japan to the position of a great power in the last half of the nineteenth century. The rise of Japan was an outstanding fact in the history of that period and it was clearly in the main, if not wholly, a traditional and not a germinal change. It took the form of a rapid absorption of European tradition. The evolution of reason has thus introduced into the problem of the causes of human history a factor which is not present in the case of other species; it has also modified the course of selection, but this, as we have seen, has not made a fundamental difference between the position of man and that of species in a state of nature.
The problem before us is therefore as follows. Owing to the fact of reproduction the population problem in both its aspects exists for all species in a state of nature and further presents fundamentally the same features for all such species. The ancestors of man were at one time subject to the same conditions from which they have, step by step, moved away owing to the development of the faculty of reason. We have to trace the causes and results of this moving away—of the progressive modifications of the conditions existing among species in a state of nature.
Though the problem has two aspects, they are closely interwoven. Changes which affect numbers also influence the quality of population. The discussion has hitherto taken the form of an introduction to the problem as a whole, and the two next chapters, the subject-matter of which will be indicated in what follows, will also be devoted to certain problems which equally bear upon both aspects of the question. From the seventh chapter onwards the two aspects are treated independently; we deal first with the quantitative and then with the qualitative aspect. Nevertheless we shall, when dealing with the quantitative problem, present evidence which we shall consider again later when treating of the qualitative problem. The book thus falls into three parts; the first six chapters are introductory to the problem as a whole, the next six chapters are concerned with problems of quantity (though many of the facts brought forward will be found also to bear later upon quality), and the following nine chapters with problems of quality. The last chapter sums up our conclusions as to the whole problem.
2. We may next ask what data are required in order that we may look into the changes away from the conditions under which the pre-human ancestor lived towards the conditions which now exist. In order that we may consider the quantitative aspect of the problem, it is evident that we require some knowledge regarding fecundity and as full details as possible regarding the factors which bear upon fertility and elimination. It is only when we are provided with such information that we can hope to be able to determine how it is that numbers are regulated among men.
In addition to such information, it will be desirable to have information regarding various social customs and the general conditions of life. As regards the inquiry into the qualitative part of the problem, it is clear that facts regarding fertility and elimination are again of value inasmuch as they throw light upon the nature and intensity of selection. For the second part of the problem it is also necessary to have in mind the main facts regarding the changes which are summed up as history into the causes of which we have to inquire; and in addition it will be necessary, in order that we may attempt some estimate of the relative importance of change in the germinal constitution on the one hand and of the other factor or factors of the nature indicated above on the other hand, to make some inquiry into the conditions which determine the nature of these latter factors. This will involve a reference to certain elementary facts of psychology together with some discussion of the origin, formation, preservation, and so on, of tradition.
If we first ask how far the data desired are available, we may afterwards go on to discuss how the facts are best presented. Our information is obviously very incomplete as regards the history of social habits and customs. Historical records do not take us farther back than at the most six thousand years, and the information available with respect to social customs, except for the latter part of the period, is very inadequate. If we take a broad view of history, written records have reference only to relatively modern times. There are two other sources of evidence upon which we have to rely and they are as follows.
Some indication of the bare outline of the course which history has taken can be gathered from a study of the fossil and cultural remains of man. The fossil remains are in the form of skeletons or portions of skeletons and the cultural remains in the shape of tools, weapons, and other traces of his mode of life that man has left behind him. It is interesting to observe that an attempt can be made to date these remains. They occur in certain strata, and estimates can be made of the length of time which has elapsed since these strata were deposited. Though a very large measure of doubt must surround any such estimates, nevertheless there is a certain measure of agreement concerning the facts which is of great interest. It is, therefore, possible to draw up a table showing these strata, together with what we should perhaps call guesses at the dates at which they began to be laid down. It can also be shown in the table what fossil and cultural remains are found in the respective strata.
The information, however, which we thus gain is very meagre. A study of fossil remains can only provide us with an outline of the facts connected with the evolution of the skeleton. More can be gathered from a study of the cultural remains, and certain deductions of considerable interest can be made especially in connexion with our present purpose so far as the evolution of skill is concerned. But, of course, we can in this manner gather nothing as to the nature of the social customs and institutions belonging to the races which practised these skilled methods. The question we have to face is whether this very bare outline of the facts of history can in any manner be filled in.
3. There is a further source of evidence which we have to consider. There has come under the observation of civilized man a large number of races in a low stage of culture. The evolution of culture or of control over the surroundings took place more quickly among certain races than among others. Some races got left out of the main stream of evolution, and finally in relatively recent years the more advanced races arrived at a stage where they were in a position completely to dominate the latter. The more primitive races were unable to offer any serious resistance to the civilized races. It was, therefore, possible to regard these primitive races dispassionately and scientifically; this study has led to the collection of a vast amount of information regarding these primitive races. These data are for many reasons often of a very unsatisfactory nature; of this the chief cause is that, before an accurate study was begun, contact with civilized races had often had a considerable influence upon the former mode of life of the primitive races. What we require and what is difficult to obtain is information as to the conditions under which these races lived before they came into contact with Europeans. With regard to the unsatisfactory nature of the evidence there will be more to say later.
It is of primary importance to observe that these races are not to be regarded as actual representatives of certain stages through which civilized races have passed. We know that in the evolution of control over nature civilized races have passed through certain stages of culture; the first stage was marked by the use of unpolished stone implements and the obtaining of food by hunting and fishing only; the second stage was marked by the use of polished stone implements and the obtaining of food by agriculture and the domestication of animals.[103] These two broad divisions—the Palaeolithic and the Neolithic—may be subdivided. But no primitive race can be regarded as representing any definite stage in exact detail, whether in the first or in the second of the two broad divisions through which civilized races have passed. While the culture of the ancestors of civilized man was evolving from that of the Palaeolithic stage to that of the present day, the culture of certain other races did not progress as far even as the Neolithic stage. But the culture of these races did not remain unmodified; it followed in each case a line of evolution of its own. These races are therefore to be regarded as specialized representatives of the earlier stages of culture through which the civilized races passed. Nevertheless, specialized though their culture may be, the general conditions of their existence are certainly similar to the general conditions which must have characterized the corresponding stage in the evolution of the culture of civilized races. That is to say, the broad features which characterize the conditions found among hunting and fishing races must also have characterized the conditions under which our Palaeolithic ancestors lived.
There is here obviously suggested a method whereby the framework of history arrived at by the evidence of fossil and cultural remains may be filled in. The broad conclusions drawn from a study of hunting and fishing races may be applied to Palaeolithic races. But this method must be used with great caution; it has undoubtedly been pressed too far. It is possible to divide hunting and fishing races into groups and to compare these groups with stages in the evolution of Palaeolithic culture. How far it is in any way valid to attribute in this fashion particular social institutions which characterize lower, middle, and upper hunting races to lower, middle, and upper Palaeolithic races respectively is very doubtful. It is not proposed here to attempt to carry the method as far as this. For one thing, so far as the subject has been worked out, there is no clear correlation between different factors affecting fertility and elimination on the one hand and stages in culture among hunting races on the other hand. Thus, as it happens, any attempt to carry this method into more detail is not productive of results, and therefore it is not worth while to inquire whether results would be valid or not. All that it is proposed to do here is to examine the evidence regarding the prevalence of certain customs, habits, and so on, among hunting races, and to apply the broad conclusions founded on this evidence to the ancestors of civilized races who supported themselves by hunting. In this manner only is it at all possible to fill in the framework of history provided by the remains of culture and by fossils, and thus to arrive at any conclusions regarding the course of the movement away from the conditions found in the pre-human ancestor to those found among civilized races.
4. With regard to the question as to the way in which this evidence may be most conveniently set out, it is proposed to proceed in the following manner. Before we come to the evidence regarding fertility and elimination, something has to be said regarding fecundity in man, and that will be the subject of the fifth chapter. In the following chapter the evidence regarding fossil and cultural remains will be very briefly discussed, just so far as, in the first place, provides the necessary historical facts to form a basis for the discussion of the qualitative problem and as, in the second place, provides the framework into which we can fit the conclusions which we shall draw from a study of primitive races. In the seventh chapter the evidence drawn from a study of hunting races will be reviewed in so far as it throws light upon fertility and elimination. In the eighth chapter the evidence bearing upon these problems, so far as the agricultural races are concerned, will be similarly set out. In the ninth chapter the evidence will be discussed in its bearing upon the quantitative problem among these races—all reference to the qualitative problem being left for later chapters. In the tenth chapter the evidence for the historical races will be similarly reviewed, and in the eleventh chapter similarly discussed. The twelfth chapter will be devoted to a discussion of certain problems connected with the quantitative problem at the present day. The twelfth chapter therefore will complete the treatment of the first or quantitative aspect of the problem, and in the remaining chapters will be discussed the second or qualitative problem. Already there will have been presented a large part of the evidence necessary for the discussion of the second problem—namely, the evidence connected with the outline of the facts of history and that connected with fertility and elimination. What other evidence is necessary can be given as and when required.
V HUMAN FECUNDITY
1. As a preliminary to the separate inquiries into the two aspects of the problem, it is necessary briefly to consider the question of human fecundity.
We may ask, in the first place, whether, taking a broad view of human history, there is any reason to believe that human fecundity has changed since the epoch of the pre-human ancestor, and, if so, whether it has increased or diminished. Secondly, there are a number of habits and customs which have been practised in different degrees at different times, such as prolonged lactation, polygamy, and so on, and we may also ask what bearing, if any, such habits and customs have upon fecundity.
There is much connected with the subject which is difficult and obscure. It is, in particular, often difficult to ascertain whether any differences in fecundity, as may be found to exist, are of the nature of racial or of environmental differences. Into such points, however, we need not go. We are concerned only with the question as to whether there are differences in fecundity, and we may confine our attention to a notice of any broad differences which do exist and to the question whether certain habits and customs widely practised at one time or another and supposed to bear upon fecundity do or do not have the influence attributed to them. We may begin with the first question set out above. In order to obtain an answer to this question we have to rely upon evidence derived from various sources, partly from primitive races, which we assume in general to exhibit conditions prevalent among prehistoric races, and partly from evidence derived from a study of the mammalian species which have been subject to changes comparable with those to which man has in the course of his history been subject.
2. From what has been said regarding the nature of reproduction in