Chapter 4

"But there is something more surprising still. Compare next the two sets of germs, the vegetable and the animal, and there is no shade of difference. Oak and palm, worm and man, all start in life together. No matter into what strangely different forms they may afterwards develop, no matter whether they are to live on sea or land, creep or fly, swim or walk, think or vegetate,--in the embryo, as it first meets the eye of science, they are indistinguishable. The apple which fell in Newton's garden, Newton's dog Diamond, and Newton himself, began life at the same point."[10]

In these remarks, of course, Drummond is dealing with the unicellular primal form, "as it first meets the eye of science"; and while certain slight peculiarities (such as the constant number of chromosomes) have been detected as characteristic of the cells of certain forms, yet for all practical purposes these words of Drummond are just as true to-day as when first written. Possibly it is because of a failure in our technique or from a lack of power in our microscopes that these wonderful protoplasmic units from which all living things originate seem identical. But it is equally possible that they _are really identical_ in structure and in chemical composition, and that only the ever present watchcare of the great Author of nature directs the one to develop in a certain manner, "after its kind," and another in still another manner, "after its kind." At any rate, the _protoplasm_ of which they are all alike composed _is_ identical wherever found, so far as any scientific tests have yet been able to determine.

[Footnote 10: "Natural Law," Chapter X.]

II

There are many varieties of single cells known to science which maintain an independent individual existence. Among the unicellular plants are the bacteria, while the unicellular animals are known as the protozoa. And although perhaps I ought to apologize to the reader for seeming to anticipate here a part of the discussion of the problem of "species," yet it seems necessary to say a few words here regarding the "persistence" of these unicellular forms.

Among the diseases which have been proved to be due to protozoa are malaria, amoebic dysentery, and syphilis; while among the much larger number which are due to bacteria, bacilli, or other vegetable parasites, are cholera, typhoid fever, the plague, pneumonia, diphtheria, tuberculosis, and leprosy.

One of the difficulties attending the study of "species" among the higher forms of plants and animals has always been the length of time required to obtain any large number of generations on which to make observations. In the case of such plants as peas, wheat, corn, or indeed almost any form of plant life, it is only with difficulty that more than one generation a year can be obtained; and when two or more generations a year are produced, they are produced under more or less unnatural conditions. So that it takes almost a lifetime carefully to test and record in a thoroughly scientific way the results of any extensive experiments regarding variation and heredity.

In the case of mice or rats or rabbits or guinea pigs, many more generations can be obtained in a few years; but in the case of the larger kinds of animals the time taken for development to maturity and for gestation is often much prolonged; and scientific observation of an exact character has been in vogue for so short a time that there has always been the chance for advocates of evolution to take refuge under the plea that, if we only had longer and more carefully conducted observations, we could really see species in the making, one form becoming transformed into a distinct form, or perhaps giving rise to another and distinct form as an offshoot.

But in the case of the bacteria and protozoa, we can have a new generation every hour or so, sometimes every half hour. True, these forms of minute life have been under observation for only a few years; but their _effects_ have in many cases been observed for almost the entire length of human history. No physician would tolerate the suggestion that the bacillus of cholera can produce the symptoms of diphtheria, or the tubercle bacillus produce the symptoms of leprosy. Nor will any scientist deny that such diseases as the plague, tuberculosis, or diphtheria are identical with diseases which ravaged Rome or Greece or Egypt thousands of years ago. And as the symptoms of these modern diseases are similar to those recorded by acute observers in Greece or Egypt two thousand years or more ago, we must conclude that the organisms causing these symptoms are doubtless identical. Similar remarks might be made regarding fermentation and other forms of decay.

In the case of a form of bacteria which reaches maturity and redivides in half an hour, the number of individual forms existing at the end of two days would need about twenty-eight figures to represent it. Doubtless these forms never multiply at this rate uninterruptedly for any great length of time, or else they would occupy the whole world to the exclusion of every other form of life. And doubtless instances arise where the period of growth to maturity and division is prolonged to several times the half-hour period mentioned above. But in any case, as we contemplate the length of time during which such well marked diseases as diphtheria, leprosy, or the plague have been known, we must acknowledge that these unicellular forms seem to _breed true_ during a most astonishingly long period. How can we deny that this "persistence" of these unicellular forms constitutes a very strong argument in favor of the "fixity" of these forms?

III

But we must proceed to examine the behavior of the various kinds of cells of which the various multicellular organisms are composed.

Plants were known to be composed of cells, and their cells were studied and described some years before it was understood that animals also are composed of cells as units. Even then, however, the first propounders of the cell theory (Schleiden and Schwann) had no clear or accurate idea of the origin of cells, or of their essential characters and structure. As to origin, they supposed that cells arose by a sort of crystallization from a mother liquor; and as to structure, they looked upon the cell-wall as the really important part, the fluid contents being quite subordinate. Hugo von Mohl (1846) applied to the fluid contents of the cell the term "protoplasm," and Max Schultze (1861) showed that this protoplasm is really identical in all organisms, plants and animals, also that the cell-wall is frequently absent in many animal tissues and in many unicellular forms, indicating that the protoplasm is the really important substance. By this time also it had become known that cells never arise _de novo_, as had been supposed by the earlier investigators, but that cells arise only by division of preexisting cells; or as Rudolf Virchow (1858) expressed it, "_omnis cellula e cellul[=a]._"

It was, however, many years before the details of the growth and reproduction of the cells (cell-division) became well understood. Not until the last quarter of the nineteenth century was it settled that the nucleus of the cell is also a supremely important part; but finally in 1882 Flemming was able to extend Virchow's aphorism to the nucleus also: _omnis nucleus e nucleo_.

Since these discoveries our knowledge of the methods of cell-division has much increased; and in the light of our modern knowledge of these matters there is nothing in all nature more marvellous than the regular orderly way in which cells reproduce themselves according to fixed laws. Certain cells in the developing embryo, for example, are early set apart for a particular function or for building certain structures, and thereafter are never diverted from this duty so as to do a different work or produce a different kind of structure. In the young embryo certain structures arise at certain predestined times in particular places, and only there and out of these cells alone. As to _why_ it should be so, we cannot tell, save as the result of deliberate design and as an expression of the order-loving mind of the God of nature. In the words of one of the greatest of modern authorities, "We still do not know why a certain cell becomes a gland-cell, another a gangleon-cell; why one cell gives rise to smooth muscle-fiber, while a neighbor forms voluntary muscle.... It is daily becoming more apparent that epigenesis with the three layers of the germ furnishes no explanation of developmental phenomena."[11]

[Footnote 11: _Nature,_ May 23, 1901.]

In accordance with the general principle of a division of labor, certain cells become early set apart to particular functions, and in accordance with the varying demands of these functions the developing cells may become greatly changed in form and in vital characteristics. That is, one cell specializes, let us say, in secretion, another in contractility, another in receiving and carrying stimuli, etc. In this way we will have the gland-cell, the muscle-cell, and the nerve-cell, each cell destined to produce one of these organs developing others "after its kind," the result being that it is soon surrounded with numerous companions doing a similar work, making up in this way a particular tissue or organ--gland, muscle, or nerve--which in the aggregate has for its function the work of the particular cells composing it.

But the important thing for us to remember in this connection is that when cells once become thus differentiated off and dedicated to any particular function, _they can never grow or develop into any distinctly different type of cell with other and different functions_. It is true that through pathologic degeneration the form and even the function of cells may become greatly changed; but never does it amount to a complete metamorphosis or complete transformation into another distinctly different type.

This is a very important principle, and it contains so many lessons for us bearing on the philosophy of life in general that it may be allowable to establish this fact by several somewhat lengthy quotations from standard authorities.

The first will be from one of the highest authorities on embryology, Charles Sedgwick Minot, of Harvard:

"In accordance with this law [of differentiation] we encounter no instances, _either in normal or pathological development_, of the transformation of a cell of one kind of tissue into a cell of another kind of tissue; and further we encounter no instances of a differentiated cell being transformed back into an undifferentiated cell of the embryonic type with varied potentialities."[12]

Again, we have the following from one of the foremost pathologists, as to the strict and rather narrow limits of even pathologic change:

"Epithelium and gland cells ... never become converted into bone or cartilage, or vice versa; while, again, it may be laid down that among epiblastic and hypoblastic tissues, on the one hand, and mesoblastic tissues on the other, there is no new development or _metaplasia_ of the most highly specialized tissues from less specialized tissues; a simple epithelium cannot in the vertebrate give rise to more complex glandular tissue, or to nerve cells; in regeneration of epithelium there is no new formation of hair roots or cutaneous glands. The cells of white fibrous connective tissue have not been seen to form striated or even non-striated muscle."[13]

[Footnote 12: _Science_, March 29, 1901, p. 490.]

[Footnote 13: J.G. Adami, "Principles of Pathology," pp. 641-642.]

As implied by these quotations, a constant and progressive differentiation of cells prevails in the developing embryo; and when complete, certain groups of cells act as specialists in doing only certain kinds of work for the body. These cells maintain their specific characters in a very remarkable degree under normal conditions. Under various abnormal conditions, however, these cells may become modified as to functions, so that cells or tissues of one type may assume more or less completely the characters of another type. "But," as a very high authority declares, "the limitations in this change in type are strictly drawn, so that one type can assume only the characters of another which is closely related to it. This change of one form of closely related tissue into another is called _metaplasia_....

"When differentiation has advanced so that such distinct types of tissue have been formed as connective tissue, epithelium, muscle, nerve, _these do not again merge through metaplasia. There is no evidence that mesoblastic tissues can be converted into those of the epiblastic or hypoblastic type, or vice versa_."[14]

[Footnote 14: Delafield and Prudden, "Text-Book of Pathology," pp. 62, 63.]

This modification of function among the cells which sometimes goes on in the developing embryo, or under pathologic conditions, is very closely analogous to the variation which goes on among species of animals and plants. But, as we shall see later, there is a well marked limit to this variation among species, just as we see there is in the variations among the cells. Practically the same general laws hold good in each case.

If cells did not maintain their ancestral characters in a very remarkable way, what would be the use of grafting a good kind of fruit onto a stock of poorer quality? The very permanency of the grafts thus produced is proof of the persistency with which cells reproduce only "after their kind."

IV

How can we fail to see the bearings of these facts on the doctrine of the transformation of species among ordinary plants and animals, which are merely isolated and self-contained groups of cells? Do not these facts constitute strong presumptive evidence that among animals and plants, though there may be variation in plenty within certain limits, perhaps within even much wider limits than used to be thought possible, yet among these distinct organisms, little and big, new forms develop only after their ancestral type, in full accord with the record given in the first chapter of the Bible?

But we are now prepared to examine in more detail the facts as now known to modern science regarding "species" of plants and animals.

V

WHAT IS A "SPECIES"?

I

We have seen that there is no way to account for the origin of matter, of energy, or of life, except by postulating a real Creation.

We have seen that cells continue to maintain their identity, and reproduce only "after their kind."

We must now deal with the higher forms of cell aggregates, which we call plants and animals. It has long been held that these at least are mutable, that one kind of plant or of animal may in the course of ages be transformed into a distinctly different type; and of late years there has accumulated a very voluminous literature dealing with the various intricacies of this problem of the origin of species. How can we deal with such a large subject in a brief way? It seems best to confine our attention in this chapter to an attempt to answer the question, What is a species? and are "species" natural groups clearly delimited by nature?

II

The term "species" was at first used very loosely by scientific writers. It meant very little more than our vague word _kind_ does at the present time. Not until the time of Linnæus (1707-1778) did the term acquire a definite and precise meaning. The aphorism of the great botanist, "_species tot sunt diversæ quot diversæ formæ ab initio sunt creatæ_"--"just so many species are to be reckoned as there were forms created in the beginning,"--was at least an attempt to use the term in a well-defined sense. Of course, this definition assumed the "fixity" of species; but with the wide prevalence of the views of Darwin and his followers the term "species" has fallen into disrepute, and is now regarded by many as only an artificial rank in classification corresponding to no objective reality in the natural world. Some writers, as Lankester, have found so much fault with the term as to urge its complete abandonment in scientific literature. This is logical enough from the standpoint of Darwinism; for if the latter be true there ought indeed to be such a swamping of every incipient "species" as to make one kind blend with others all around it in the classification series.

But since the term has by no means been discarded, we must endeavor to determine the sense in which it continues to be used in good scientific literature.

"A species," says Huxley, "is the smallest group to which distinct and invariable characters can be assigned." The Standard Dictionary says that the term is used for "a classificatory group of animals or plants subordinate to a genus, and having members that differ among themselves only in minor details of proportion and color, and are capable of fertile interbreeding indefinitely."

The latter authority also adds:

"In the kingdoms of organic nature species is founded on identity of form and structure, and specifically characterized by the power of the individuals to produce beings like themselves, who are in turn productive."

To put the matter still more definitely before the reader, we quote the following from a well-known scientist whose writings on the subject of evolution have had a wide circulation:

"There are two bases on which species may be founded. Species may be based on _form_, morphological species; or they may be based on _reproductive functions_, physiological species. By the one method a certain amount of difference of form, structure, and habit, constitutes species; according to the other, if the two kinds breed freely with each other and the offspring is indefinitely fertile, the kinds are called varieties, but if they do not they are called species."[15]

This author adds that this physiological test, as to whether or not the kinds are cross fertile, "is regarded as a most important test of true species, as contrasted with varieties or races."

[Footnote 15: Joseph Le Conte, "Evolution and Religious Thought," p. 233.]

III

When we look at the matter in this light, it is very evident that there are multitudes of long recognized specific distinctions that ought to be discarded. For instance, there are some twenty odd "species" of wild pigs scattered over the Old World, which Flower and Lydekker assure us would probably "breed freely together."[16] The yak and the zebu of India, and the bison of America, would on this basis have to be surrendered, for it is well known that they will all breed freely with the common domestic cattle, as well as with one another. Perhaps all or nearly all of the dozen or more "species" of the genus _Bos_ would thus be included together. All of the dogs, wolves, and others of the _Canidæ_ might thus be considered as fundamentally a unit. The cats (_Felidæ_) are well known to breed freely together, Karl Hagënbeck of Hamburg having crossed lions and tigers as well as others of the family. Practically all of the bears have been crossed repeatedly, and the progeny of these and other crosses are quite familiar sights at the London Zoölogical Gardens. Among the lower forms of life even more surprising results have been attained by Thomas Hunt Morgan and others.

[Footnote 16: "Mammals Living and Extinct," pp. 284-285.]

It would, however, be a very hasty conclusion to say on the basis of these facts that there are no natural limitations to groups of animals and plants. But we are entirely warranted in concluding from these facts that in very many cases, perhaps in most, our system of taxonomic classification of animals and plants has gone altogether too far, and that scientists have erected specific distinctions which are wholly uncalled for and which confuse and obscure the main issues of the species problem. Among the workers in botany and in every department of zoölogy there have always been the "splitters" and the "lumpers," as they are familiarly called; the former insisting on the most minute distinctions between their "species," thus multiplying them; the latter being more liberal and tending to diminish the number of species in any given group. For a generation or more in the recent past the "splitters" had things pretty much their own way; but of late there is a growing tendency to frown down the mania for creating new names. Even yet it is with the utmost reluctance that long established specific distinctions are surrendered, as is illustrated in the case of the mammoth, which is acknowledged by some of the very best authorities to be really indistinguishable from the modern Asiatic elephant. Several fossil bears were long listed in scientific books; but they are all acknowledged now to be identical with the modern grizzly, and as we have already intimated all the modern ones ought to be put together. These modern rationalizing methods have made but a slight impression on the vast complex of the fossil plants and animals, affecting the names of only a few of the larger and better known forms. In the realm of invertebrate palæontology, however, the "splitters" are still holding high carnival, in spite of the efforts of some very prominent scientists in the opposite direction. For palæontologists still follow the irrational course of inventing a new name, specific or even generic, for a form that happens to be found in a kind of rock widely separated as to "age" from the other beds where similar forms are accustomed to be found. As Angelo Heilprin expresses it, "It is practically certain that numerous forms of life, exhibiting no distinctive characters of their own, are constituted into distinct species _for no other reason than that they occur in formations widely separated from those holding their nearest kin_."[17]

As a result of these methods this same author declares: "It is by no means improbable that many of the older _genera_, now recognized as distinct by reason of our imperfect knowledge concerning their true relationships, have in reality representatives living in the modern seas."[18]

[Footnote 17: "Geographical and Geological Distribution of Animals," pp. 183, 184.]

[Footnote 18: _Id_., pp. 207, 208.]

But the situation is very little better when we come to deal with plants and animals of our modern world. Because, with the many thousands of students of natural science all over the world, each anxious to get into print as the discoverer of some new form, the systematists have a dead weight of names on their hands that by a rational and enlightened revision could doubtless be reduced to but a fraction of their present disheartening array. For as the result of the extensive breeding experiments now being carried on under the study of what is called Mendelism (a term that will be explained in the next chapter), it has been found that great numbers of the "species" of the systematists or classificationists will not stand the physiological test of breeding, that is, they are found to breed freely together according to the Mendelian Law. As William Bateson remarks:

"We may even be certain that numbers of excellent species recognized by entomologists or ornithologists, for example, would, if subjected to breeding tests, be immediately proved to be _analytical varieties_, differing from each other merely in the presence or absence of definite factors."[19]

The following from David Starr Jordan, the leading American authority on fishes, will serve to show how numerous have been the new names invented in recent years, all tending further to confuse and complicate the problem of what is a species:

"In our fresh-water fishes, each species on an average has been described as _new_ from three to four times, on account of minor variations, real or supposed. In Europe, where the fishes have been studied longer and by more different men, upwards of six or eight nominal species have been described for each one that is now considered distinct."[20]