Robert Wright’s The Moral Animal: The New Science of Evolutionary Psychology offers the general audience a survey of research in the field that has come to be known both as sociobiology and as evolutionary psychology. Building upon the studies of Edward O. Wilson, Robert Trivers, George Williams, and William Hamilton, Wright develops an evolutionary model through which he seeks to explain various aspects of modern society. According to Wright, the roots of contemporary behavior should be sought not in modern society itself but in those tendencies and desires that would have enhanced a person’s reproductive success during the early history of evolution.
Unlike the Social Darwinists of the late nineteenth and early twentieth centuries, Wright does not regard “the survival of the fittest” as a model for modern behavior. The author carefully distinguishes between tendencies that may have been productive in his hypothetical “ancestral environment” and those that are socially productive today. In addition, he explains how such diverse traits as altruism, marital infidelity, sibling rivalry, and parental love may have evolved through their ability to enhance survival or reproduction in the most primitive of human communities.
Wright’s basic premise may be summarized as follows: If any genetically based behavior increases, even marginally, the likelihood that a person will reproduce, then this behavior will be favored by natural selection. Over the course of time, the genes leading to this behavior will spread throughout a population at the expense of genes that have little or no survival value. One illustration of this pattern would occur when genetically based tendencies lead an animal to produce large numbers of offspring, all of which have the same genetic code and the same behavioral tendencies. Something similar would occur in the case of genes encouraging people to protect their families. Since close relatives share a large amount of genetic information, benevolence toward kin causes one’s own genetic code to prosper as it is spread by siblings and cousins.
Arguments such as these are unlikely to persuade anyone who views environment, rather than heredity, as the leading factor in determining human personality. Nor do they prove conclusively that human behavior is genetically based as Wright claims or that his hypothetical “ancestral environment” could have existed in the age before a united protohuman species divided to form races, cultures, and societies scattered across the globe. Nevertheless, much of Wright’s argument is compelling. For example, his suggestion that sexual infidelity may originate in a form of reproductive strategy seems particularly convincing. In early hunting and gathering communities, successful reproductive strategies must have been distinctly different for the two sexes. For men, frequent relationships with large numbers of women inevitably led to more offspring. For women, sexual relationships with a large number of men did not necessarily result in a larger number of pregnancies. Thus, in Wright’s “ancestral environment,” it was in a woman’s reproductive interest to be highly selective about her partners; by succumbing only to men who were “rich,” strong, and healthy, women ensured that their offspring would have the greatest chance to survive and produce children of their own. For men, a successful reproductive strategy relied not so much upon quality as upon quantity. The predisposition to engage in sexual unions indiscriminately would have been favored by natural selection simply because it led to larger numbers of equally promiscuous (male) children.
These differences in reproductive strategy also help explain why men may be more likely than women to leave their partners for younger mates. A man’s period of sexual potency is lengthy; by finding a younger partner, a man may extend his reproductive opportunities by ten to twenty years. On the other hand, switching mates does not in most cases increase a woman’s reproductive potential. To the contrary, an older, more established male may increase a woman’s survivability, as well as that of her children, while a younger partner lacking in social status may not have the capacity to provide adequate support for her family.
This bleak image of male evolutionary progress is not, however, the sole message of The Moral Animal. Because human children have a prolonged period of vulnerability, men who are predisposed toward greater “parental investment” increase the likelihood that their offspring will survive. In addition, the greater sexual selectivity of females means that men’s willingness to care for children may increase their possibilities of finding willing sexual partners. As a result, in comparison to other species—even other primates—human males show relatively high...
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