“For example, skin color (like sex) is genetically transmitted, but there is no reason to believe that either is biologically linked to IQ. The measurement of high heritability might simply reflect the fact that skin color (like sex) provokes certain expectations that are themselves transmitted from generation to generation—not biologically, but culturally, or environmentally. It has been shown that such social expectations can have dramatic effects on performance (., on measures of IQ). So IQ might be passed on from generation to generation, but here the mechanism of transmission is mediated not by causal factors that (like genetic or more generally biological factors) are internally transmitted from parent to child, but rather by causal factors (cultural biases) that are socially handed down through the generations. In other words, we cannot predict the technical heritability of a trait even when it is known to be genetic, and we cannot predict whether a trait is genetic even when it has been shown to have high heritability.”
Genetics had a major role in the confirmation and elaboration of Darwin’s theory of evolution. Evolutionary genetics (including population genetics) investigates the genetic mechanisms of selection and the role of individual genes, genetic systems, and the mutation process in evolution. The Soviet geneticist S. S. Chetverikov made a fundamental contribution to population genetics in 1926 by combining in a single concept the ideas of Mendelism and Darwin’s theory of evolution. The development of evolutionary and population genetics was considerably advanced by the American scientist S. Wright and the English scientists J. Haldane and R. Fisher, who in the 1920’s and 1930’s laid the foundation for mathematical-genetic methods and the genetic theory of selection. Soviet scientists, especially N. P. Dubinin and D. D. Romashov, but also N. V. Timofeev-Resovskii, as well as the school of T. G. Dobzhansky in the USA, did much to advance experimental population genetics.
It may seem surprising, but genetic influence on behavior is a relatively recent discovery. In the middle of the 20th century, psychology was dominated by the doctrine of behaviorism, which held that behavior could only be explained in terms of environmental factors. Psychiatry concentrated on psychoanalysis, which probed for roots of behavior in individuals’ early life-histories. The truth is, neither behaviorism nor psychoanalysis is incompatible with genetic influences on behavior, and neither Freud nor Skinner was naive about the importance of organic processes in behavior. Nevertheless, in their day it was widely thought that children’s personalities were shaped entirely by imitating their parents’ behavior, and that schizophrenia was caused by certain kinds of “pathological mothering.” Whatever the outcome of our broader discussion of nature–nurture, the basic fact that the best predictors of an adopted child’s personality or mental health are found in the biological parents he or she has never met, rather than in the adoptive parents who raised him or her, presents a significant challenge to purely environmental explanations of personality or psychopathology. The message is clear: You can’t leave genes out of the equation. But keep in mind, no behavioral traits are completely inherited, so you can’t leave the environment out altogether, either.