Through much of the twentieth century, biologists and social scientists debated whether human behavior was governed primarily by inherited characteristics or by the environment in which a person grew up. Biologists stressed the role of genes in controlling the development of living things, while psychologists and sociologists investigated the impact of subjective experience and the social milieu upon individuals. Each discipline found convincing evidence for its view and concluded that the other approach was mistaken.
Matt Ridley objects to this either/or dichotomy and argues that proving one belief correct does not necessarily prove the other concept wrong. He maintains that recent studies demonstrating how the environment affects the ways in which genes are expressed, combined with data showing how genes influence behavior, provide an understanding of how heredity and environment actually cooperate in producing human behavior.
“Learning,” Ridley states, “could not happen without an innate capacity to learn. Innateness could not be expressed without experience. The truth of each idea is not proof of the falsehood of another.” He concludes that “the more we discover genes that influence behavior, the more we find that they work through nurture; and the more we find that animals learn, the more we discover that learning works through genes.”
Ridley is hardly the first to suggest that both genetic and environmental factors govern individual development. Many scientists have tried to find a balanced position providing a just consideration of the way nature and nurture interact. Ridley, however, brings to his task both a familiarity with the latest genetic research and an engaging writing style that has made him an outstanding popularizer of biological science.
Modern studies of human twins show how genes can triumph over environment. Identical twins sharing the same genes, when separated at birth and raised in very different families, behave in amazingly similar ways. In contrast, fraternal twins, experiencing the same prenatal experiences and raised together, usually behave in very individualistic manners. Studies of primate behavior, however, demonstrate the powerful effect of environment in modifying the expression of comparable genetic endowment.
Of the approximately thirty thousand human genes transcribed by the Human Genome Project, from 95 percent to nearly 99 percent are identical with those of the great apes. One of the few sharp distinctions between humans and other primates is that humans possess one less chromosome. At some point in the past, two middle-sized ape chromosomes fused to form the exceptionally large human chromosome 2. The source of the divergence between humans and apes, Ridley stresses, lies not in different genes but in the same set of genes being used in a different pattern. The consequence of the genetic similarity of the great apes is that they all resemble one another physically—skeletons of large chimpanzees have been mistakenly identified as small gorillas and gorillas as large chimpanzees.
Ridley uses examples drawn from ethological research on primates to show that, despite the physical resemblance, some behavior can be affected more by environment than by genes, even when involving as universal an instinct as sexual behavior. The genetic basis for sex would be very similar in gorillas and chimpanzees, but expression of such genes is heavily influenced by different habitats and food-gathering practices. Gorillas are herbivores. Plants are abundant in the African jungle but not very nutritious. The gorilla must eat almost continuously but need not move very far; therefore, a group of gorillas can easily be defended. A male gorilla that grows to great size can assemble a harem of females and effectively hold off competitors. Chimpanzees eat fruit primarily—supplemented with insects and monkey meat, when they can get it. Because fruit is widely disseminated, the chimpanzee needs a large range, which is easier to defend by an alliance of males sharing the favors of their associated females. There is no great advantage for chimpanzees in being much larger than average. Adapting to their environment, chimpanzee males are only slightly larger than females, while gorilla males are nearly twice as large as females.
As Ridley examines various aspects of the interaction of nature and nurture, he provides many acute observations. He cites the paradox that the more equal society is, the more heritability matters, and the more genes affect outcomes. In a true meritocracy, in which all receive equal opportunity and equal training, the outstanding athletes would be the ones whose genes are best adapted to...
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