Chapter 5

[Footnote 19: "Mendel's Principles of Heredity," p. 284, 1909.]

[Footnote 20: "Science Sketches," p. 99.]

And again:

"Thus the common Channel Catfish of our rivers has been described as a new species not less than _twenty-five times_, on account of differences real or imaginary, but comparatively trifling in value."[21]

[Footnote 21: "Science Sketches," p. 96.]

Perhaps the reader will tolerate another somewhat long quotation because of the light which it sheds on this whole problem.

"Some years ago we had a parasite of a very destructive aphid down in our books as _Lysiphlebus tritici_. In carrying out our investigations it became necessary to find out whether this parasite had more than a single host insect, and whether it could develop in more than one species of aphid. To this end, recently emerged males and females were allowed to pair, after which the female oviposited in several species of aphids. Both parents were then killed and preserved and all of their progeny not used in further experiments were also preserved, and thus entire broods or families were kept together. In this way females were reared out of one host species and allowed to oviposit in others, until, often after several hosts had been employed, it would be bred back into the species whence it first originated. In all cases the host was reared from the moment of birth, while with the parasite both parents and offspring were kept together.

"The result of this little fragment of work _was to send two genera and fourteen species to the cemetery_--you may call it Mt. Synonym Cemetery, if you choose--while the insect involved is now _Aphidius testaceipes_. The systematist who studies only dried corpses will soon be out of date."[22]

[Footnote 22: F.M. Webster, of the U.S. Dept. of Agriculture, in _Science_, April 12, 1912, p. 565.]

IV

Now all this is not given to intimate that there is no scientific justification for the term "species," but to make plain to my non-professional readers what every well-informed biologist already knows, namely, that at the present time the "species question" is still in a very unsatisfactory state. The facts given above would strongly suggest that there probably is indeed such a thing as a species, in the sense assigned by Linnæus, who as we have seen wished to make it a designation covering all the descendants of each distinct kind originally created. But this original aim of Linnæus is to-day not merely ignored but treated with lofty contempt; for according to the prevailing theories of evolution, all the manifold diversities of life in our modern world have come about gradually as the result of a slow development by natural process, and hence it would be vain beyond measure to attempt to determine the limits of a "species" in the sense understood by Linnæus.

But we may conclude, from the facts presented above, that if there is such a naturally delimited group as a "species" in the Linnæan sense of the word, it by no means coincides with what now passes under this name, but might include many so-called species, often a whole genus, or even several.

With this in mind, we must pass on to consider the next step in our study, as to whether new "species" are now coming into being in our modern world under scientific observation, either natural or artificial.

VI

MENDELISM AND THE ORIGIN OF SPECIES

"Had Mendel's work come into the hands of Darwin, it is not too much to say that the history of the development of evolutionary philosophy would have been very different from that which we have witnessed."[23]

[Footnote 23: William Bateson, "Mendel's Principles of Heredity," p. 316.]

I

From the latter part of the eighteenth century, attempts were continually being made to explain the origin of all organic forms by some system of development or evolution. Buffon had dwelt on the modifications directly induced by the environment. Lamarck had made much use of this idea, claiming that such modifications were transmitted to posterity, and claiming the same for the structural changes produced by use and disuse. Lamarck's work did not become at all popular while he lived, chiefly through the overpowering influence of Baron Cuvier, who had an equally fantastic scheme of his own, which may well be termed a burlesque on Creation and in which an extreme fixity of "species" was a cardinal doctrine. Erasmus Darwin and Robert Chambers in England also tried to make a theory of evolution believable; though their efforts were but little more successful in gaining the ear of the world.

But to all that had gone before Charles Darwin and A.R. Wallace (1858) added the idea of "natural selection," or "the struggle for existence," to use the respective terms coined by each of these authors, as the chief means by which the effects of variation are accumulated and perpetuated so as to build up the modern complexities of the plant and animal kingdoms. Partly because it was a psychological moment, from the fact that the uniformitarian geology of Lyell with its graded advance of existences from age to age seemed absolutely to demand some evolutionary explanation; partly because artificial selection was a familiar idea of proved value in selective breeding, and "natural selection" seemed an exact parallel carried on by nature in the direction of continual improvement; but perhaps more largely because the abstract idea of "natural selection" involved so many intricate separate concepts that for nearly a generation scarcely two naturalists in the world could state the whole problem of the theory exactly alike;--on all these accounts the theory of natural selection, or of the "survival of the fittest," to use the phrase of Herbert Spencer, became in the latter decades of the nineteenth century well-nigh universal.

But about 1887 a faction or school arose who criticized the main idea of Darwin and Wallace and fell back on the Lamarckian factor of the transmission of acquired characters as really the essential cause of the process of evolution. Herbert Spencer, E.D. Cope and others did much to criticize natural selection as inadequate to do what was attributed to it, dwelling on the importance of the transmission of acquired characters. Spencer even went so far as to declare, "either there has been inheritance of acquired characters, or there has been no evolution." These Neo-Lamarckians argued that natural selection alone can neither explain the origin of varieties, nor the first steps in the slow advance toward "usefulness." An organ must be already useful before natural selection can take hold of it to improve it. Selection cannot make a thing useful to start with, but only (possibly) make more useful what already exists. Until the newly formed buds of developing limbs or organs became decidedly "useful" to the individual or the species, would they not be in the way, merely so many hindrances, to be removed by natural selection instead of being preserved and improved? But, in this view of the matter, they argued, what single organ of any species would there be that must not thus have appeared long before it was wanted?

Or to use the pungent words quoted with approval by Hugo de Vries at the end of his "Species and Varieties" (pp. 825, 826), "Natural selection may explain the survival of the fittest, but it cannot explain the arrival of the fittest."

This side of the argument is dwelt upon at some length by Alex. Graham Bell, as reported in a recent interview. He says:

"Natural selection does not and cannot produce new species or varieties or cause modifications of living organisms to come into existence. On the contrary, its sole function is to prevent evolution. In its action it is destructive merely,--not constructive,--causing death and extinction, not life and progression. Death cannot produce life; and though natural selection may produce the death of the unfit, it cannot produce the fit, far less evolve the fittest. It may permit the fit to survive by not killing them off, if they are already in existence; but it does not bring them into being, or produce improvement in them after they have once appeared."[24]

[Footnote 24: _World's Work_, December, 1913, p. 177.]

Opposing these Neo-Lamarckians were such prominent scientists as August Weismann, A.R. Wallace, E. Ray Lankester, who strenuously opposed the idea that "acquired characters," or more precisely _parental experience_, are ever transmissible. In the subsequent years the greatest variety of experimental tests have been applied to secure the hereditary transmission of any sort of such acquired characters, with uniformly negative results. One of the most elaborate of these experiments was conducted by a German botanist, who transplanted 2,500 different kinds of mountain plants to the lowlands, where he studied them for several years alongside their relatives, natives of these lowlands. He found that their mountain environment had made absolutely no permanent change in their structures or habits, which soon conformed exactly with those of their relatives which had lived in the lowland environment for centuries. Many similar efforts have been made to confirm this doctrine of the transmission of acquired characters; but their universal failure is like that of mechanics in trying to invent perpetual motion.

Thomas Hunt Morgan sums up the present situation in the following words: "To-day the theory has few followers among trained investigators, but it still has a popular vogue that is wide-spread and vociferous." And we may add that the extent of its spread is directly proportioned to the need felt for this doctrine as a support of the theory of evolution, while the vociferance of its advocates is inversely proportioned to the evidence in its support.

As a result of extensive modern experiments and discussion, biologists have grown very cautious, and are by no means so positive as they were twenty years ago in affirming just _how_ species have come into existence. Echoes of this old controversy between the two leading schools of biologists are occasionally heard; but the enthusiasm with which they set out a half century ago to solve the riddle of plant and animal life has largely given way to a purpose to discard speculation and patiently to observe and record actual facts. For with natural selection discredited in the house of its friends, and Lamarckianism under grave suspicion from want of a single well authenticated example, it is hard to see what there is left of the biological doctrine that has so dominated scientific thought for a half century. If each of these opposed schools of scientists are right in _what they deny_, the whole theoretical foundation for the origin of new kinds of animals and plants is swept away,--absolutely gone. For if an individual really cannot transmit what he has acquired in his lifetime, how can he transmit what he has not got himself, and what none of his ancestors ever had? And if natural selection cannot start a single organ of a single type, what is the use of discussing its supposed ability to improve them after the machinery is all built?

II

Such was the general condition of theoretical biology about the beginning of the present century. In the meantime those who were dealing with the empyrical or experimental side of these problems were seeking for the causes of and the rules for variation. All living things vary from one generation to another; the question was, Why do they vary? and do these variations really represent new characters comparable to new species in the making? or are they, so to speak, but an elastic reaction of the internal vital elasticity of the organism, all the while latent and only seeking a favorable expression, to return again under other conditions to the former type?

The effort to reduce these variations to law and system was pursued by thousands of investigators, with varying but at all times perplexing and disappointing results. But in the year 1900 the scientific world awoke to the surprising fact that a patient obscure investigator had already solved most of the puzzles of variation and heredity some thirty-five years before. Gregor Mendel, born a peasant boy, trained as a monk, and afterwards appointed Abbot of Brünn, had in the year 1865 published the results of his experiments in breeding, which had been ignored or forgotten until rediscovered in 1900 by de Vries and two others simultaneously. From this point Mendelism, as it is now called, has steadily gained ground, until at the present time it can be said to be the dominating conception among biologists the world over regarding the problems of heredity.

Mendel worked chiefly with peas, crossing different varieties. In his methods of investigation he differed from all previous investigators in concentrating his attention upon a single pair of alternative or contrasted characters at a time, and observing how these alternative characters are transmitted.

Thus when he crossed a tall with a dwarf, giving attention to this pair of contrasted characters alone, he found that all the first hybrid generation were talls, with no dwarfs and no intermediates. Accordingly he called the tall character _dominant_, and the dwarf character _recessive_, and a pair of contrasted characters which act in this way are now called _factors_ or sometimes called _unit characters_. But on allowing these hybrids to cross-fertilize one another in the usual way, Mendel found that in the second generation of hybrids there were _always_ _three talls to one dwarf_ out of every four. Further experiments proved that these dwarfs of the second hybrid generation _always bred true_, that is, one out of four; and that one out of the remaining talls always bred true, making another quarter of the total; while the remaining fifty per cent. proved to be mixed tails, always acting as did the original hybrids, splitting up in the next generation in the same arithmetical proportion as before.

Accordingly, if we confine our study to the two contrasted characters, tallness and dwarfness, we see that just three kinds of peas exist, namely, dwarfs which breed true, talls which breed true, and talls which always give the same definite proportion of talls and dwarfs among their descendants. Innumerable experiments which have since been made with other pairs of characters have demonstrated that this same mathematical proportion holds good throughout the whole world of plants and animals;[25] and hence this astonishing result is now called Mendel's Law, and is regarded as the most important discovery in biology in several generations.

[Footnote 25: When dealing with only a few individual cases, we do not always find them to come out in such exact proportion; but when the number of examples is large, the proportion is so close to these figures that the exceptions can be entirely neglected as probably due to error of some kind.]

There are two distinct kinds of Andalusian fowls, one pure bred black, the other pure bred white with slight dashes of black here and there. When these are mated, no matter which color is the father or the mother, the next or hybrid generation are always a queer mixture of black and white called by fanciers blue. When these blues are interbred, one-quarter of their offspring will be white, which will prove to breed true ever afterwards, one-quarter will be black that will breed true, and fifty per cent. will be blue which will break up in the next generation in the very same way as before. In this case neither white nor black character is dominant, and accordingly we have a blending of both in the first hybrid generation.

In guinea pigs, black color has been found to be dominant over white, rough coat over smooth coat, and short hair over long hair. These remarkable results following from an experimental trial of Mendelism have stimulated hosts of investigators in all parts of the world, until now many varieties of plants and animals have been studied for many successive generations, already, building up a considerable literature dealing with the subject.

Perhaps the most extensive and exact series of experiments along this line have been carried on by Thomas Hunt Morgan and his assistants, of Columbia University. For over five years they have been breeding the wild fruit fly (_Drosophila ampelophila_), during which time they have originated and observed over a hundred and twenty-five new types that breed true according to Mendel's laws. Every part of the body has been affected by one or another of these mutations. The wings have been shortened, or changed in shape, or made to disappear entirely. The eyes have been changed in color or entirely eliminated. And each of these wonderful variations was brought about not gradually, but at _a single step_.

Professor Morgan grows justifiably sarcastic in contrasting these demonstrated laboratory facts with the armchair theories that have so long and so harmfully dominated biological studies. A quotation from him will not be out of place at this point.

"I may recall in this connection that wingless flies also arose in our cultures by a single mutation. We used to be told that wingless insects occurred on desert islands because those insects that had the best developed wings had been blown out to sea. Whether this is true or not, I will not pretend to say; but at any rate wingless insects may also arise, not through a slow process of elimination, but at a single step.... Formerly we were taught that eyeless animals arose in caves. This case shows that they may also arise suddenly in glass milk bottles, by a change in a single factor."[26]

[Footnote 26: "A Critique of the Theory of Evolution," p. 67.]

We need not be particularly concerned here with the theoretical explanations of these facts offered in terms of the microscopic or even the infra-microscopic components of the germ cells. Morgan seems to make out a strong case for the theory that the chromosomes found in the nucleus are the real ultimate units that carry the hereditary factors. But he is quite decided in the opinion that these hereditary factors are fixed, and are not changed from generation to generation either by environment or by selection.[27] The important thing for us in this connection is to get a clear idea of the results following from an application of Mendel's laws to the old, old problem of the origin of species, incidentally noticing how the theory associated with Darwin's name now looks in the light of these new facts.

[Footnote 27: In human beings it has been found that the effects of alcoholism and of syphilis are indeed transmitted according to Mendelian law, being the two solitary examples of diseased conditions that are thus transmitted. But they are so plainly pathologic phenomena that there is little temptation for the advocates of Lamarckianism to use them as proofs of their theory.]

We have hitherto been considering the results worked out by Mendel with but one pair of contrasted characters or factors. But Mendel studied the relation of other characters of the pea, and found among other results that smooth seeds are dominant to wrinkled seeds, colored seeds dominant to white, yellow color dominant to green, etc. But when a combination of _two_ factors in each parent are put into contrast by cross breeding, two wholly original forms (as they seemed) were sometimes produced, and it looked as if these new kinds were really analogous to new species.

For example, he crossed tall yellow peas with dwarf green peas, with the result that the first hybrid generation turned out to be all tall yellows. However, in the second hybrid generation they split up according to the law as already stated, modified by the additional complication brought into the problem by the additional pair of factors. For out of every sixteen plants there were nine tall yellows, three _dwarf yellows_, three _tall greens_, and one dwarf green. It is evident that these tall greens and dwarf yellows are really new forms; and further experiments proved that they can be separated out or segregated and grown as pure forms which thereafter breed true. Thus we have a very important result for the breeder, for it enables him to work to a definite aim and combine certain desirable characters into a single form.

The term _mutation_, as already intimated, has been given to this process of producing new varieties in this way. The kinds so produced are termed _mutants_, and at first they were hailed by enthusiastic scientists as "elementary species." De Vries in particular gave much publicity to this idea; for he thought he had really produced a new kind comparable in every respect to a true species as produced by nature among wild plants. But the enthusiasm with which this applied result of Mendel's Law was at first hailed by biologists has gradually subsided; for it has been found that though these new forms will breed true under certain conditions, they are nevertheless _cross-fertile with the original forms_, and thus the circle can be _completed back again_ by a return to the parent form, from which the new "species" can again be produced at will with the same mathematical exactness as before.

III

Where then are we?

Clearly we have not really produced any new species in any correct sense of the word. If we have produced new forms that breed true and that are seemingly just as deserving of the rank of distinct species as many now listed in scientific books, it only shows that our lists are sadly at fault, and that they are not all species that are called species. These experiments merely indicate that _the parent form possesses more potential characters than it can give expression to in a single individual form_, some of them being necessarily latent or hidden, and that when these latent ones show themselves they must do so at the expense of others which become latent or hidden in their turn. This _vital elasticity_, as it may be termed, or the vital rebound under definite conditions, is indeed a prime characteristic of the species just as it is of the individual; but like that of the individual the vital elasticity of the species is strictly bounded by comparatively narrow limits beyond which we have never seen a single type pass under either natural or artificial conditions. Mutations can be made according to Mendel's Law; but when we have made them once _we can always be sure of producing the_ _very same mutants again in the very same way_, as surely as we produce a definite chemical compound; and when we have made it _we can always resolve it at will back into its original form_, just as we can a chemical compound. And so, where is the evolution? or how do these facts throw any light on the problem of the origin of species, any more than chemical compounds throw light on the origin of the elements? Obviously in biology as in chemistry we are only working in a circle, merely marking time.

And the bearing of these facts on the other problem of the transmission of acquired characters is quite obvious. Mendelism provides no place for any such transmission. Mendel's Law is sometimes called the law of _alternative inheritance_, thus embodying in its name the thought that offspring may show the characters possessed by one parent or by the other, but that it cannot develop any characters whatever which were not manifest or latent in the ancestry. Changes in the environment during the embryonic stage, it is true, seem sometimes to be registered in the growing form; but it has never yet been proved that these induced changes can ever amount to a unit character or genetic factor that will maintain itself and segregate as a distinct factor after hybridization. Ancestry alone furnishes the material for the factor, and no amount of induced change can get itself registered in the organism so as to come into this charmed circle of ancestral characters which alone seem to be passed on to posterity.