Nature-Nurture Debate

The social and behavioral sciences have in recent years played host to what has come to be called the “nature versus nurture debate.” This is the question of to what degree our genes (“nature”) explain human differences in certain phenotypic variables such as intelligence, personality predispositions, criminal tendencies, and so on, versus the degree to which the social environment (“nurture,” which includes many social structural variables such as schooling, one's social class status, one's parent's or parents' social class status, one's family socialization practices, nutrition, peer group influences, and so on) also explain intelligence, personality, and criminal tendencies.

Comprising part of this debate is the question of whether and to what extent there is interaction between genes and environment upon intelligence or personality predispositions. This is the issue of whether and to what extent the effect of genes depends upon what social environment(s) the individual is raised in, and also whether the effect of social environment itself depends upon a person's genes. Thus gene–environment interaction would be present if both genes and environment combine in particular ways to account for a person's intelligence and/or personality.

The whole issue is a debate, because while some researchers argue that the effect of genes is the greatest (in the neighborhood of 70 percent, if expressed as a percentage, thus leaving only 30 percent to social environment and gene–environment interaction), other researchers argue that the effect of the social environment is the greatest, comprising 50 percent or more of the effect on intelligence and personality. Then there are researchers who argue that gene–environment interaction is the largest component, though they are reluctant to place a percentage estimate on its effects.

The evidence and the methodology of the genetic effect as well as the effect of social environment lead to the conclusions (a) that the effect of genes on intelligence (and personality), though estimated by some researchers in the past to be “high” at around 70 percent, is instead more in the neighborhood of 50 percent, and very possibly less, in the neighborhood of 30 to 40 percent, if appropriate new methodological considerations are introduced; (b) that the effect of the many variables in the social environment (assuming for the moment that gene–environment interaction is zero) is at least 50 percent, and very probably more; and, further, that (c) while gene–environment interaction is no doubt a reality, it is not empirically estimable at the present time. So leaving aside the question of gene–environment interaction, the nature-nurture debate boils down to the question of whether the effects of genes on intelligence and personality predisposition are greater than or approximately equal to the effects of the social environment, or whether the effects of the social environment are greater.