Genes, brains, and culture: Returning to a Darwinian evolutionary psychology

Behavior and Philosophy, 2001 by Rushton, J Philippe

A commentary on Death, Hope, and Sex by James S. Chisholm. Cambridge, UK: Cambridge University Press, 1999, 296pp.

Chisholm's central thesis is that the life histories of individual human beings (i.e., reproductive strategies, speeds of maturation, testosterone levels, mateseeking and risk-taking behaviors-even age at death) are contingent upon stability of parenting. For Chisholm, desirable social-behavior traits, which emphasize long-term planning and conscientiousness, emerge from a background of predictable attachments, whereas antisocial, impulsive, and self-destructive traits result from unpredictable experiences. As one who early applied r-K life-history theory to human differences (Rushton, 1985), I applaud Chisholm's attempt to understand the particulars of human behavior in terms of the big picture of the evolution of hominoid life cycles. Unfortunately, his book is weakened by its failure to examine the genetic side of the coin.

Whether people provide stable environments for their children, or for themselves, and how they react to a variety of stresses and traumas, as well as other challenges and opportunities (even being wounded in combat; see True et al., 1993), is partly a function of the genes they inherit. Unfortunately, Chisholm is at a complete loss on how to unravel the nature-nurture conundrum, describing gene x environment interactions as "conceptually vapid" and relegating behavior genetic studies to a footnote (p. 71). His take-home message, that mind and morality are mainly a function of the family culture the child grows up in, is the conventional wisdom.

Chisholm and I once debated behavioral genetics following his publication in Current Anthropology of an early version of his book (Chisholm, 1993, 1994; Rushton, 1994). It is disappointing that he has still not come to grips with this material. A clue to why is offered by a secondary theme of his book, that there exists an "intense moral task of political planning" in that governments have a duty to ensure that all people grow to be equally empathic and with equal opportunity to "maximize future reproduction" (pp. 237-238). Perhaps he believes his political agenda would be compromised by any admission that individual life outcomes are partly due to genetic differences. (He begins his Preface with S. J. Gould's favorite quote from Darwin: "If the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin.") Regardless, since in science ignorance is never to be preferred over knowledge, however supportive ignorance may be to a political agenda, I will expand on some of what I wrote in my earlier critique.

Twin and adoption studies have repeatedly demonstrated that people inherit their personalities and temperaments, their attitudes and values, and a whole complex of behaviors including mate-preferences and parenting-styles (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990; McGuffin, Riley, & Plomin, 2001). As almost everyone now accepts, especially in the wake of the Human Genome Project, genes plainly do contribute significantly to people's temperaments, abilities, and patterns of interest. They even help create the individual differences in empathy, nurturance, altruism, and aggression (Rushton, Fulker, Neale, Nias, & Eysenck, 1986) that Chisholm makes the basis for his Theory of Mind. But rather than present these data and tell his readers what, if anything, is wrong with them, Chisholm dismisses the issue.

By ignoring Bouchard's famous studies of similarity in identical twins raised apart, Lumsden and Wilson's (1981) path-breaking work on gene-culture coevolution, and Scarr's (1996) work on how children develop their own niches, he misses the point that genes work to channel development across many unpredictable gene-environment interactions. If they did not, adopted-away siblings would not grow to become so similar in their values and attitudes, with their degree of later resemblance being predicted by the number of genes they share. I review much of this literature in Chapter 3 of my book Race, Evolution, and Behavior (1995, 2000, 3rd ed.) and won't do it again here. I shall, however, point to several excellent and highly readable introductions (e.g., Harris, 1998; Reiss, Neiderhiser, Hetherington, & Plomin, 2000; Segal, 1999).

Behavioral geneticists typically find that a 50% genetic plus 50% environmental model fits the data better than either purely genetic or purely cultural alternatives (such as Chisholm's Attachment Theory). Genes provide an initial set point, along which environmental factors then move individuals up or down the continuum of reproductive strategies. The genetic leash, as Lumsden and Wilson (1981) note, may be a very long one, but it is nonetheless a very real and a very strong one. Only genetically-informed research designs (such as those using twins and siblings reared apart or adoptees) can pluck the flower of causation from the nettle of conflicting interpretation.

Another crucial topic sidestepped by Chisholm is IQ. He grants that intelligence is an adaptation to allow for tracking environments, and it is one component of his Theory of Mind, but for Chisholm it plainly takes a back seat to empathy. Thus, he ignores 100 years of research which show that the general factor of intelligence (g), plays a substantial role in predicting people's adjustment, and thereby misses the single best predictor of social and economic success in Western society (Schmidt & Hunter, 1998; also Jensen, 1998). Low IQ also predisposes an individual to a number of less desirable life outcomes. As shown by Herrnstein and Murray (1994) in The Bell Curve, these include dropping out of school (-0.50), being dependent on welfare (-0.45), being absent from work for 4 weeks due to injury or sickness (-0.30), having a first child out of wedlock (-0.26), and if married, being divorced within 5 years (-0.14), and, if pregnant, continuing to smoke (-0.14)!