It will be admitted by every one that a part of the body which is much used tends to increase in size, or strength, and similarly that a part which is not used tends to atrophy. It is further found that such changes are progressive in the race, in many cases. Man's brain has steadily increased in size, as he used it more and more; on the other hand, his canine teeth have grown smaller. Can this be regarded as the inheritance of a long continued process of use and disuse? Such a view is often taken, but the Lamarckian doctrine seems to us just as mystical here as anywhere else, and no more necessary. Progressive changes can be satisfactorily accounted for by natural selection; retrogressive changes are susceptible of explanation along similar lines. When an organ is no longer necessary, as the hind legs of a whale, for instance, natural selection no longer keeps it at the point of perfection. Variation, however, continues to occur in it. Since the organ is now useless, natural selection will no longer restrain variation in such an organ, and degeneracy will naturally follow, for of all the variations that occur in the organ, those tending to loss are more numerous than those tending to addition. If the embryonic development of a whale's hind leg be compared to some complicated mechanical process, such as the manufacture of a typewriter, it will be easier to realize that a trivial variation which affected one of the first stages of the process would alter all succeeding stages and ruin the final perfection of the machine. It appears, then, that progressive degeneration of an organ can be adequately explained by variation with the removal of natural selection, and that it is not necessary or desirable to appeal to any Lamarckian factor of an unexplainable and undemonstrable nature.
The situation remains the same, when purely mental processes, such as instincts, are considered. Habit often repeated becomes instinctive, it is said; and then the instinct thus formed by the individual is passed on to his descendants and becomes in the end a racial instinct. Most psychologists have now abandoned this view, which receives no support from investigation. Such prevalence as it still retains seems to be largely due to a confusion of thought brought about by the use of the word "instinctive" in two different senses,—first literally and then figuratively.
A persistent attempt has been made in America during recent years, by C. L. Redfield, a Chicago engineer, to rehabilitate the theory of the inheritance of the effects of use and disuse. He has presented it in a way that, to one ignorant of biology, appears very exact and plausible; but his evidence is defective and his interpretation of his evidence fallacious. Because of the widespread publicity, Mr. Redfield's work has received, we discuss it further in Appendix B.
Since the importance of hormones (internal secretions) in the body became known, it has often been suggested that their action may furnish the clue to some sort of an inheritance of modifications. The hormone might conceivably modify the germ-plasm but if so, it would more likely be in some wholly different way.
In general, we may confidently say that there is neither theoretical necessity nor adequate experimental proof for belief that the results of use and disuse are inherited.
(4) When we come to consider whether the effects of the environment are inherited, we attack a stronghold of sociologists and historians. Herbert Spencer thought one of the strongest pieces of evidence in this category was to be found in the assimilation of foreigners in the United States. "The descendants of the immigrant Irish," he pointed out, "lose their Celtic aspect and become Americanised.... To say that 'spontaneous variation,' increased by natural selection, can have produced this effect, is going too far." Unfortunately for Mr. Spencer, he was basing his conclusions on guesswork. It is only within the last few months that the first trustworthy evidence on the point has appeared, in the careful measurements of Hrdlička who has demonstrated that Spencer was quite wrong in his statement. As a fact, the original traits persist with almost incredible fidelity. (Appendix C.)
In 1911, Franz Boas of Columbia University published measurements of the head form of children of immigrants[14] which purported to show that American conditions caused in some mysterious manner a change in the shape of the head. This conclusion in itself would have been striking enough, but was made more startling when he announced that the change worked both ways: "The East European Hebrew, who has a very round head, becomes more long-headed; the south Italian, who in Italy has an exceedingly long head, becomes more short-headed"; and moreover this potent influence was alleged to be a subtle one "which does not affect the young child born abroad and growing up in American environment, but which makes itself felt among the children born in America, even a short time after the arrival of the parents in this country." Boas' work was naturally pleasing to sociologists who believe in the reality of the "melting-pot," and has obtained widespread acceptance in popular literature. It has obtained little acceptance among his fellow-anthropologists, some of whom allege that it is unsound because of the faulty methods by which the measurements were made and the incorrect standards used for comparison.
The many instances quoted by historians, where races have changed after immigration, are to be explained in most cases by natural selection under new conditions, or by interbreeding with the natives, and not as the direct result of climate. Ellsworth Huntington, the most recent and careful student of the effect of climate on man,[15] finds that climate has a great deal of influence on man's energy, but as far as inherited traits in general are concerned, he is constantly led to remark how little heredity is capable of being changed.
Most members of the white race have little toes that are partly atrophied, and considerably deformed. In many cases one of the joints has undergone ankylosis—that is, the bones have coalesced. It is confidently alleged that this is due to the inheritance of the effects of wearing tight shoes through many centuries. When it is found that the prehistoric Egyptians, who knew not tight shoes, suffered from the same defect in a similar degree, one's confidence in this kind of evidence is much diminished.
The retrogression of the little toe in man is probably to be explained like the degeneration of the hind leg of the whale, as a result of the excess of deteriorating variations which, when not eliminated by natural selection, lead to atrophy. Since man began to limit the use of his feet to walking on the ground, the little toe has had much less value to him.