What Is Heredity?

Abstract

The discussion in Scienice precipitated by the statement of Professor Dice, that 'the characters of man that are inlclude not onily his anatomical features, but also his physiology ancd his psychology, has served to emphasize the need of clarificationi of the coneept of heredity. Expressions like inherited skinl or iinherited are figures of speech which are misleading if taken literally. The relations betweeni heredity and characters or traits of the developing organism are dynamic. Heredity does niot transmit skin colors or behaviors; it determines the responses. the normyi of reactioni, of the organism to its environment. The same heredity in different environments may give rise to differenit skin colors anld behaviors. Diabetes mellitus is inherited, but injections of insulin remove the manifestations of this physiological disorder. Insulini obviously does not cure or alter the defective heredity; but this heredity responds to an envirolnmenit which contains inisullin by normal carbohydrate metabolism. Now, it is not too much to suppose that a diabetic will in some cases behave differently from a noni-diabetic. The former is likely to adhere to a certain regimen wvlhieh miiight, for example, limit hiis social activities. He mlay be reluctaint to embark on a journey in parts where he is not sure to findl a supply of insulin. His wvhole personality miiay acquire a special cast which in the last analysis is dlue to the possession of genes for diabetes. A Negro, or for that m-latter anybody having a higThly pigmnented skin, imiay be diffidenit or aogressive in a social environment in which his pigmelntation subjects him to discriminlation and handicaps. This psychology miiay correctly be called inherited, just as the skini color is called iiiherited, although in some peo ple the skin color is greatly changed byT exposuLre to sunlight. Heredity which causes the skini to be black andl behavior self-conscious miiay result in a quite different behavior in an environment where discrimlinatioln is abselnt. Noni-geneticists may feel dlisineilned to regard as a trait so plastic that it appears in some environments but not in others. Yet, all degrees of environnmental plasticity occur. For example, the A-aB-a blood group genies produce the same character in all knowni environmients. The outward manifestationis of the genes for eye color slightly chanoes with age. The environmental dependenciee of stature, weight an-d skin color is obvious. Behavior is influenced so much by environmental variables, particularly training, social conditions ancd accumLulated experience, that the genetic variable is frequently masked. The designatioln hereditary can not be restricted to traits which show a certaini deoree of constaney of expression. The degree of constancy is itself in-iconstanit; introductioni of insulin treatmenits malde the expression of the genes for diabetes much mlore labile than it was. It miay seem trite to reminicd that genes inifluenee the developmiient through chainis of physiological reactions. The possibilities of controlling the gene manifestation will be greatly inereased when these reactions become kniown. Theoretically, the action of a-ny gene mnay be X Repriiited, wvitli mlinlor cihanges, fromii Science, Vol. 100, p. 406, Nov. 3, 1944.