The theory of inheritance of acquired traits has gone by the board; biologists no longer accept it. Such traits as an individual's tanned skin acquired by living in the tropics, horny hands acquired by hard labor, immunity to measles acquired by having measles, big muscular development acquired by gymnastics, are not transmitted by heredity to the children of the individual who acquired these traits.
Nor are acquired behavior traits transmitted by heredity. Learned reactions are not so transmitted, knowledge is not, acquired skill is not. Learn to cook, to typewrite, or pilot an airplane as perfectly as possible, and your child will still have to learn all over again. You may make your experience valuable to him by teaching him, but not in the way of heredity.
Language affords a good test of this matter. A child's parents, and all his ancestors for many generations, may have spoken the same language, but that does not relieve the child of the necessity of learning that language. He does not inherit the language habits of his ancestors. He has no native tendency to say "dog", or "chien", or "hund", on sight of this animal. Here in America we have children born of stocks that have spoken foreign languages for many generations; but English becomes their "native tongue" after a generation or two here, that is to say, as soon as the child hears English from infancy.
In short, there is no likelihood whatever that any instinct [{114}] ever originated out of a habit or learned reaction. If we could believe it had so originated, that would furnish an easy explanation of the origin of an instinct; but it is contrary to all the known facts.
Instincts Not Necessarily Useful in the Struggle for Existence
Some of the best-known instincts, such as feeding or mating--or hunting, or flight from danger, or the hibernation of frogs--are so essential for the survival of the individual or the propagation of the next generation that we tend to assume that all instinctive behavior has "survival value", value, that is, towards the survival of the individual or of the race. But this is an assumption, and it seems not to be borne out by actual observations of instinctive behavior, since, along with the definitely useful reactions, others occur that would seem to have no survival value. Perhaps the crowing of the rooster at dawn would be a case in point; or the elaborate bowing that is observed in some kinds of birds. And there are the less definite, rather random movements of squirming, kicking, running about, wrinkling up the face, etc., that appear in young animals. We may well hesitate before definitely asserting that these movements are of no use for survival, but at least their use is not obvious, and there is no reason for assuming that all instinctive behavior must necessarily be useful.
To be sure, the "struggle for existence" would eliminate individuals who behaved in ways that seriously handicapped them in procuring food or escaping from enemies; and therefore we should not expect to find really harmful instincts preserved in the race. But a mode of behavior might be neutral in this respect, or even slightly disadvantageous, and yet not be weeded out unless the struggle for existence were very keen.
The main point is that the psychologist should take instinctive behavior as he finds it, and not allow himself to be prejudiced by the assumption that instinct must necessarily be useful. That has to be shown in each case, not assumed at the outset.