Human Traits and their Social Significance

by Irwin Edman

In general the influence of heredity may be said far to outweigh the influence of home training. In all the cases reported, the resemblances were about the same in traits subject to training, and in those not subject to training. Thus industry and conscientiousness and public spirit, which are clearly affected by environment, show no greater resemblance than such practically unmodifiable traits as memory, original sensitiveness to colors, sounds, and distances.

The influence of parentage, it must be added, consists in the transmission of specific traits, not of a certain "nature" as a whole. There are in the germ and the ovum which constitute the inheritance of each individual, certain determinant elements. The elements that determine the original traits with which each individual will be born vary, of course, in the germs produced by a single parent less than among individuals chosen at random, but they vary none the less. In this variation of the determining elements in the germs of the same individual is to be found the cause of the variation in the physical and mental traits among children of the same parents.

Since the determining elements, the unit characters that appear in the sperm or ovum of each individual, do not appear uniformly even in children of the same parents, brother and sister may resemble each other in certain mental traits, and differ in others. "A pair of twins may be indistinguishable in eye color and stature, but be notably different in hair color and tests of intellect."

Mental inheritance, as well as physical, is, then, organized in detail. It is not the inheritance of gross total natures, but of particular "mental traits." If we had sufficient data, we should be able to analyze out the unit characters of an individual's mental equipment, so as to be able to predict with some accuracy the mental inheritance of the children of any two parents. In the case of physical inheritance, the laws of the hereditary transmission of any given traits are known in considerable detail. The detailed quantitative investigations of inheritance, following the general lines set by Mendel, have given striking results.

Physical traits have been found to be analyzable into unit-characters (that is, traits hereditarily transmitted as units), such as "curliness of hair," "blue eyes," and the like. Mental traits, however, do not seem analyzable into the fixed unit-characters prescribed by the Mendelian laws of inheritance.

The success which breeders have had in the control of the reproduction of plants and animals, in the perpetuation of a stock of desirable characteristics and the elimination of the undesirable, has given rise to a somewhat analogous ideal in human reproduction. That eugenics has at least its theoretical possibilities with regard to physical traits, few biologists will question. However difficult it may be in practice to regulate human matings on the exclusive basis of the kind of offspring desired, it is a genuine biological possibility. In a negative way, it has already in part been initiated in the prevention of the marriage of some extreme types of the physically unfit, by the so-called eugenic marriage laws in some states in this country.[1]

[Footnote 1: There have been laws, as there is a fairly decided public opinion, adverse to reproduction by the feeble-minded and the morally defective. But (see Richardson: The Etiology of Arrested Mental Development, p. 9) there have been a number of cases of feeble-minded parents producing normal children.]

But whether scientific regulation of marriages for the production of eugenic offspring is feasible, even apart from the personal and emotional questions involved, is open to question. No mental trait such as vivacity, musical ability, mathematical talent, or artistic sense, has been analyzed into such definitely transmissible unit-characters as "blue eyes" and "curliness of hair." So many unit-characters seem to be involved in any single mental trait that it will be long before a complete analysis of the hereditary invariable determinants of any single trait can be made.

It is thus impossible to tell as yet with any security or precision the biological components of any single mental trait. The evidence at our disposal, however, does confirm us in the belief that one of the most significant and certain causes of individual differences, whether physical or mental, is immediate ancestry or family. Individuals are made by what they are initially, and, as we shall presently see, therefore largely by their inheritance. With the latter, environment can do just so much, and no more. And the most significant and effective part of an individual's inheritance is his family for some generations back, rather than the race to which he belongs.

The influence of the environment. Those factors so far discussed which determine individual differences are independent of the particular conditions of life in which an individual happens to be placed. An individual's race, sex, family are beyond modification by anything that happens to him after birth. Maturity, in so far as it is mere growth independent of training, is also largely a fixed and unmodifiable condition.