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 a.s.sistants, 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 gla.s.s 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 a.s.sociated 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 a.n.a.logous 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 pa.s.s 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 pa.s.sed on to posterity.
A quotation from Bateson ought to set this point at rest:
"The essence of the Mendelian principle is very easily expressed. It is, first, that in great measure the properties of organisms are due to the presence of distinct, detachable elements [factors], separately transmitted in heredity; and secondly, that _the parent cannot pa.s.s on to offspring an element, and consequently the corresponding property, which it does not itself possess_."[28]
[Footnote 28: _Scientific American_ Sup., January 3, 1914.]
Heredity we now see is a method of a.n.a.lysis, and the facts brought to light by Mendelism help us very much toward an understanding of living matter. Especially does it help us to understand the complexity underlying the facts of heredity, which until now have seemed so strange and capricious. As Professor Punnett of Cambridge remarks:
"Const.i.tutional differences of a radical nature may be concealed beneath an apparent ident.i.ty of external form. Purple sweet peas from the same pod, indistinguishable in appearance and of identical ancestry, may yet be fundamentally different in their const.i.tution. From one may come purples, reds, and whites; from another only purples and reds; from another purples and whites alone; whilst a fourth will breed true to purple. Any method of investigation which fails to take account of the radical differences of const.i.tution which may underlie external similarity, must necessarily be doomed to failure. Conversely, we realize to-day that individuals identical in const.i.tution may yet have an entirely different ancestral history. From the cross between two fowls with rose and pea combs, each of irreproachable pedigree for generations, come single combs in the second generation, _and these singles are precisely similar in their behavior to singles bred from strains of unblemished ancestry_. In the ancestry of the one is to be found no single over a long series of years; in the ancestry of the other nothing but singles occurred. The creature of given const.i.tution may often be built up in many ways, but once formed it will behave like others of the same const.i.tution."[29]
[Footnote 29: Encyclopaedia Britannica, Vol. XVIII, p. 119.]
IV
Vanished at last are the old theories of gradual changes in species perpetuated and acc.u.mulated by natural selection until at last wholly new forms have in this way been produced. True variations are now seen to be confined within well-marked and rather narrow limits, within which ordinary variations may occur, perhaps induced by environment. These fluctuating variations grade off into one another on all sides, and their differences _can_ be plotted on a frequency curve; but the very important thing for us to remember is that these fluctuating variations _cannot be transmitted._ Beyond these fluctuating variations come the unit characters or factors, which are distinct from each other, or "discontinuous," to use the technical term, and which therefore _cannot be plotted on a frequency curve_. These factors are not modified in the least by the environment, and their peculiarities are faithfully transmitted in heredity with all the precision of chemical law. But even these factors are all within the bounds of the species. There is not a shred of scientific evidence that either natural or artificial devices have originated a single genetic factor that was not all the time potentially latent in the ancestry, capable of being produced at will by the proper combination.
It is a universal law of living things that all forms left to themselves tend to degenerate. The necessity for continuous artificial selection in the sugar beet, in Sea Island cotton, in corn, in Jersey and Holstein cattle, in trotting horses, proves this universal tendency to degenerate.[30] Natural selection in a somewhat similar way tends to postpone this degeneracy by killing off the "unfit," but selection either artificial or natural cannot originate anything new, and its results are here displayed merely among the small fluctuating variations mentioned above. Even among the real genetic factors it may show itself by allowing some to survive alone; but as no combination of diverse factors can originate anything really new, its field for operation among these factors is extremely limited. Among species also it is operative, killing off some and allowing others to survive. But neither among fluctuations, among factors, nor yet among species can selection originate anything new.
[Footnote 30: The following represents the consensus of scientific opinion regarding the lessons to be drawn from the phenomena of our improved races of domesticated plants and animals:
"One need not be a pessimist to a.s.sert the actual evidence thus far obtained indicates that the supposed progress made in the improvement of domesticated animals and plants is nothing more than the sorting out of pure lines, and thus represents no advancement."--Prof. L.B. Walton, _Science_, April 3, 1914.]
Nor is there any other method known to modern science by means of which new factors can be originated which were not potentially latent in the ancestry. The much heralded new "species" of de Vries and others are now known to be merely new factors cropping out;[31] for though they remain constant and breed true, they obey Mendel"s Law when crossed with their parental forms, and hence are merely the result of some new combination of factors which can be reproduced at will by using the same method of combination and segregation. The real scientific test for any form supposed to be a new "species" would be twofold: (1) to show that some new character had been added which no ancestor ever possessed; and (2) to show that this new character will breed true under all circ.u.mstances of hybridization and not merely segregate as a unit character or mere a.n.a.lytic variety after hybridization. It is almost superfluous to say that no "new species" originating in modern times has ever justified itself under these tests.
[Footnote 31: Some of our leading biologists are now disposed to grow somewhat humorous when speaking of this mutation theory of de Vries, as may be ill.u.s.trated by the following:
"The mutation theory of de Vries appears accordingly to lag useless on the biological stage, and may apparently be now relegated to the limbo of discarded hypotheses.... The present refutation has been undertaken in the interest of biological progress in this country. It is now high time, so far as the so-called mutation hypothesis, based on the conduct of the evening primrose in cultures, is concerned, that the younger generation of biologists should take heed lest the primrose path of dalliance lead them imperceptibly into the primrose path to the everlasting bonfire."--Prof. Edw. C. Jeffrey (Harvard), in _Science_, April 3, 1914.]
In conclusion it may be remarked that biologists do not claim to have solved all the problems connected with heredity and variation. But the general results taught us by Mendelism are now established beyond controversy. Led by the German biologists, the leading scientists of the world had already acknowledged that "pure" Darwinism or natural selection cannot explain the origin of new organs or new forms. And now Mendelism destroys the other supposed foundation for biological evolution, by showing that small variations cannot be acc.u.mulated into large differences equal in value to a unit character or a new species.
Thus the whole foundation of biological evolution has been completely undermined by these new discoveries; and were it not for the wide-spread credence the evolutionary theory has already received, and the intellectual momentum it has acquired tending to carry it on by its inertia into the future, it could be only a very short time now before the elaborate treatises attempting to orientate with it all the facts of religion and history would have to be consigned to the shelves labeled, "Of Historic Interest." For as Bateson remarked in his recent address as President before the British a.s.sociation at Melbourne, Australia, the new knowledge of heredity shows that whatever evolution there is occurs by loss of factors and not by gain, and that in this way the progress of science is "destroying much that till lately pa.s.sed for gospel."[32]
[Footnote 32: In commenting on these views of Bateson, Prof. S.C. Holmes, of the University of California, well speaks of them as "an ill.u.s.tration of _the bankruptcy of present evolutionary theory."--Science_, September 3, 1915.]
V
Let us sum up the situation. We began this chapter with the question, Have new kinds of plants and animals originated in modern times comparable in all essential respects with the idea of true species?
The answer of modern science is reluctantly obtained, but it is a negative. De Vries and others have indeed originated new kinds that were loudly hailed as new species, and are doubtless as deserving of specific rank as many already listed for years in the treatises of specialists.
Indeed there is every reason to believe that almost countless numbers of our taxonomic species have originated from common ancestral originals.
But as these so-called species are now known to be freely or moderately cross fertile with other related species, their hybrids following the ordinary laws of Mendelian inheritance, we see that they are not true species but mere a.n.a.lytic varieties.
In short, we now know that our taxonomic cla.s.sifications have been marked off on altogether too narrow lines. This has tended greatly to confuse the question at issue. But from our enlarged views of the laws and nature of heredity and variation, as well as from the original intent of the term _species_ as defined by the great scientist who originated it, the verdict of an impartial investigator must be that we have never seen a new species originate by any natural or artificial method since the dawn of scientific observation.
Here again we find the record of Creation confirmed; for the failure of the thousands of modern investigators to originate genuine new species proves that in this respect also Creation is not now going on. And all the a.n.a.logies from the origin of matter, of energy, of life, and from the laws of the reproduction of cells, indicate that we have at last found rock bottom truth regarding the vexed question of the origin of species. So far as science can observe and record, each living thing on earth, in air, in water, reproduces "after its kind."
VII
GEOLOGY AND ITS LESSONS
I
In all the previous chapters I have not been giving any very new facts or any discoveries of my own. True, my conclusions from the facts may seem novel; but in general I have been giving merely facts which are almost universally acknowledged by educated men. The conservation laws of matter and of energy, the impa.s.sable gulf between the living and the not-living, the laws governing cell multiplication, are matters of common knowledge and will be found in the appropriate college text-books throughout the civilized world. Even the facts which I have presented regarding variation and heredity are admitted in one way or another by practically all biologists. But in following our general subject into the field of geology, I shall be obliged to present some comprehensive truths and general conclusions which are not so widely acknowledged, because only recently brought to light. However, as these facts and conclusions may seem very new and strange to many, I shall endeavor to build up my argument wholly on the recorded observations of the very highest authorities rather than on my own unsupported testimony; though for the sake of brevity I shall be obliged to refer the reader to my "Fundamentals of Geology" (1913) for some of the details.
One of the great outstanding ideas of geology as usually taught is that life has been on the globe for many millions of years, that in fact there has been a graded succession of different types of life in a well defined invariable order, from the lower and more generalized to the higher and more specialized. Quite obviously this succession of life was antagonistic to the former views of a literal Creation; and only on this supposed fact as an outline has the modern theory of biological evolution been built up. For if geology cannot furnish the most unquestionable proof that life has occurred in a very definite and invariable order, what is the use of talking about the development of one form of life into another by a gradual process of evolution?