Rarefaction

“ The majority cling to their belief in the Lamarckian factors.
The only safe conclusion to which we can come is that the question as to inheritance of acquired characters has still to be answered.
Evolution depends on Variation and Heredity. The problems of Variation and Heredity are now being attacked from many sides by biologists. It is on their solution that all advance in future must depend. ”

“ Every one must have heard of cases of albinism, prickly skin, hairy bodies, &c., appearing in several members of the same family. If strange and rare deviations of structure are truly inherited, less strange and commoner deviations may be freely admitted to be inheritable. Perhaps the correct way of viewing the whole subject, would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly. ”

“ It does not follow that because the father and son have black hair, or the mother and daughter have blue eyes, or that their mannerisms are similar, that inheritance is responsible for character, much less for crime. Certain things are clearly traceable to heredity. Other things may be the result of association or what to us must still be accident.
Often the fact is pointed out that great progress has been made in the culture of plants and the breeding of animals. This is true. No intelligent farmer to-day would think of raising any but the best stock. ”

“ A sort of purposeless mania seems to fall upon many of them, and they might as well get together a lot of old bottles or stones as moths. They deceive each other as to the locality for their rarities. I have even heard of one rabid collector, now happily deceased, who destroyed every specimen he had or could buy up of a certain rare exotic species, except one pair in his own collection, so that he could say he was the only one who had it! ”

“ The wonder, indeed, in all cases is not that any character should be transmitted, but that the power of inheritance should ever fail. The checks to inheritance, as far as we know them, are, firstly, circumstances hostile to the particular character in question; secondly, conditions of life incessantly inducing fresh variability; and lastly, the crossing of distinct varieties during some previous generation, together with reversion or atavism-that is, the tendency in the child to resemble its grand-parents or more remote ancestors instead of its immediate parents. ”

“ But if the new be too foreign, we cannot fuse the old and the new—nature seeming to hate equally too wide a deviation from ordinary practice and none at all. This fact reappears in heredity as the beneficial effects of occasional crossing on the one hand, and on the other, in the generally observed sterility of hybrids. If heredity be an affair of memory, how can an embryo, say of a mule, be expected to build up a mule on the strength of but two mule-memories? Hybridism causes a fault in the chain of memory, and it is to this cause that the usual sterility of hybrids must be referred. ”

“ Thus we are led to the conclusion that the acquisition of habits by the individual during his efforts to adapt himself to his environment, and transmitted down a long line of genealogical descent, is the method of heredity; and further, that man, in common with other animals, inherits all these racial and individual acquirements from his parents. Instinct, we have said, may be termed the "Suggestion of Heredity," which again is "race memory," or the evolutionary product of habits acquired during the process of man's adaptability to his environment. ”

“ An hereditary soul which revives the ancestor has always its black feather, owing to the fact that it is the result of a unique combination, since it exists in the sheath, the body, which is hereditary to the same extent. ”

“ There is nothing to show the necessary non-inheritance of acquired characters. The only evidence which one can recognize as good, is that which makes equally in favour of the theory of stirp—or rather, of the well-known fact that congenital characters are at any rate much more heritable than are acquired: which, it is needless to repeat, is a widely different thing from proving—or even rendering probable—the absolute restriction of germ-plasm to a separate “sphere” of its own “since the origin of life.” ”

“ Everything may be transmitted by heredity, even to the finest shades of sentiment, intelligence and will, even to the most insignificant details of the nails, the form of the bones, etc. But the combinations of ancestral qualities vary so infinitely that it is extremely difficult to recognize them. Hereditary dispositions arise from the energy of two conjugated germs during the whole of life and till death. Old people sometimes develop peculiarities hitherto unknown in them, owing to the fact that one or more of their ancestors also presented the same phenomena at an advanced age. ”

“ How then can we rely upon use-inheritance for the improvement of the race? Even if it is not a sheer delusion, it may be more detrimental as a positive evil than it is advantageous as an unnecessary benefit; and as a normal modifying agent it is miserably weak and untrustworthy in comparison with the powerful selective influences by which nature and society continually and inevitably affect the species for good or for evil. ”

“ We can best understand the laws governing the inheritance of traits by taking a few concrete cases. The first case is that of an Andalusian fowl. We shall consider the two species, pure bred black and pure bred white, and confine ourselves to observing the inheritance of the single characteristic, plumage color. Of course, as long as the black mate only with the black their children will be black, and as long as the white mate with white the children will be white. But if a white mates with a black, the children will not be either black or white, but blue. All will be blue. ”

“ The first is that heredity undoubtedly exists, or there would be no such thing as a family likeness, and every marriage might suddenly produce a small negro. The second is that even simple heredity can never be simple; its complexity must be literally, unfathomable, for in that field fight unthinkable millions. But yet again it never is simple heredity: for the instant anyone is, he experiences. ”

“ From the hereditary nature of all characteristics, whether good or bad, we learn the importance of having all desirable qualities thoroughly inbred; or, in other words, so firmly in each generation that the next is warrantably certain to present nothing worse—that no ill results follow from breeding back to some inferior ancestor—that all undesirable traits or points be, so far as possible, bred-out. ”

“ As we proceed along the line we meet gaps which slay the theory of genealogical descent altogether. A gap is fatal to it. If a family dies out, that is the end of it. You can not resuscitate it after a few centuries, and go on with that breed; much less can you pick up a breed quite different, and attach it to your old genealogy. But in the line of evolution we meet these fatal gaps; and no evolutionist has bridged them, because they can not possibly be bridged. ”

“ There is one thing that always puzzles me: as inheritors of the mentality of our reptile ancestors we have improved the inheritance by a thousand grades; but in the matter of the morals which they left us we have gone backward as many grades. That evolution is strange, and to me unaccountable and unnatural. ”

“ But it is possible, with present knowledge, to say that human traits, mental as well as physical, are inherited, in a high degree. Even before the final details as to the inheritance of all traits are worked out—a task that is never likely to be accomplished—there is ample material on which to base action for eugenics. The basal differences in the mental traits of man (and the physical as well, of course) are known to be due to heredity, and little modified by training. ”

“ Even those who still believed in what is conventionally called "the inheritance of acquired characteristics" would be quick to repudiate any such application of the doctrine as is commonly made by most of the philanthropists and social workers who are proceeding without seeking the light of biology. But the idea that these modifications are inherited is so widespread among all who have not studied biology, and is so much a part of the tradition of society, that the question must be here examined, before we can proceed confidently with our program of eugenics. ”

“ But this increasing difficulty of complex evolution is only overcome by some favourably-varying individuals and species—not by all. And as the difficulty [23] increases we find neglect and decay of the less-needed faculties—as with domesticated animals and civilized men, who lose in one direction while they gain in another. The increasing difficulty of complex evolution by natural selection is no proof whatever of use-inheritance [10] except to those who confound difficulty with impossibility. ”

“ If on the other hand the specific characters in question are not inherited they must be acquired afresh by each generation. On this view acquired characters would play an important part in the origin of species though a very different part to that which is usually ascribed to them by the Lamarckians.
There is another possible way in which acquired characters might play an important part in organic evolution even though it should be finally proved that such characters are never transmissible by inheritance. ”

“ Often pedigree-experiments lead to poor races, betraying their tendency to deviate only from time to time and in rare cases. Such instances constitute what we have called in a former lecture, "half races," and their occurrence indicates that the casual observation of an anomaly is not in itself adequate to give an opinion as to the chance of repetition in sowing experiments. A large number of species seem to belong to this case, and their names may be found in the above mentioned work by Masters and elsewhere. ”

“ If a spirit of false pride leads genealogists to hold aloof from these experiments, they will make slow progress. The interpretation of genealogy in the light of modern research in heredity through the experimental breeding of plants and animals is full of hope; without such light, it will be discouragingly slow work. ”

“ The ordinary facts of inheritance illustrate continuity of causation—very conspicuously where varieties so distinct as negro and white are united, and where traces of the negro come out generation after generation ”

“ Nearly all the polygenistic arguments are included in the following:—“The difference between the Negro and the White is too great for them to belong to the same species.” These types are the two extremes in the human series. Therefore, if it can be shown that between the two extremes, the limits of variation are almost always greater in plants and animals than in man, we shall have undermined the foundation of the whole polygenistic doctrine. ”

“ There remains the terminological difficulty that, as I have tried to show, the individual may display characters which were potential in the germ, inherent and necessarily inherited, though they did not appear in the parent nor yet in any ancestor. We have to face the paradox, then, that in natural inheritance a parent can transmit what he has not got, though this does not apply to the unnatural inheritance of property in human society. ”

“ Without inheritance the establishment of a stock would be impossible, and without a stock, variations and mutations would be chaotic and without significance. Thus, ever since Darwin's own attempt at a theory of heredity, we find the students of organic evolution and the breeders of plant and animal races alike devoting themselves to the problems of racial and individual inheritance. ”

“ That existing forms of life have been evolved from other forms, and that these ancestral forms have been different from those derived from them, is shown by the occasional appearance of antecedent and abandoned types of structure among the offspring of existing species. Occasionally a human child is born strangely unlike its parents, but bearing an unmistakable resemblance in looks and disposition to his great-grandfather or some other remote ancestor. This is atavism, that tendency to revert to ancestral types which is prevalent among all animals. ”

“ Following analogy, we ought to look for a tribe of human beings that had degenerated into apes. That we find no such recessive characteristics even among the most degenerate savages, and no such ape-like tribe of human beings, is a decisive proof that man never descended from the brute. Else such recessive characteristics, according to the Mendelian Law, would be sure to appear. We would also find monkeys and apes,—the recessive species—descended from man. ”

“ No one can doubt the law of hereditary transmission. Our inherited and acquired characteristics are sure to be transmitted to our descendants. Indeed, so thoroughly does character permeate one's entire being that it might be said of each drop of blood that in its characteristics it is a miniature of the person in whose body it was secreted. Eminent characters do not emanate from degenerate parents; and neither is the reverse true, except as the result of adequate reversionary influences. ”