Cultural Group Selection

Review of A Different Kind of Animal: How Culture Transformed Our Species. By Robert Boyd. Princeton University Press. 229 pp. $27.95.

Charles Darwin’s theories have stood the test of time. In The Origin of Species, Darwin laid out three conditions in which natural selection would generate cumulative adaptation: 1) a struggle for existence in which not all individuals reproduce; 2) variation in rates of reproduction; 3) variation that is heritable. Convinced that his theory of evolution applied to human beings, Darwin subsequently made a claim that has been rejected by many biologists. In Descent of Man, he maintained that important features of human sociality originated in selection among groups with different behavioral standards—a result that required substantial heritable variation among groups.

Robert Boyd, a professor of Human Behavior and Social Change at Arizona State University, believes Darwin was right. In A Different Kind of Animal, Boyd makes the case that in addition to genetic differences and individual learning, a process he calls cultural group selection” has created differences in norms among human societies.

These norms (which are enforced by sanctioning violators) “provide a scaffold” for sharing decisions, limiting the scope of internal and external conflict, and making the group more competitive.

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The format of A Different Kind of Animal helps readers understand the fundamentals of Boyd’s theory and challenges to it. In two splendid essays, Boyd draws on mathematical modeling, rational choice and game theories, and studies he conducted in Fiji and elsewhere, to defend his claim that cultural adaptation is “the core ingredient” in the ecological success of human beings. Four responses (by a biologist, a philosopher, an economist, and an anthropologist) follow. The volume then gives Boyd the last word.

Spread through imitation of individuals who are deemed to have useful knowledge rather than by individuals figuring out how things work, these norms include dietary taboos for pregnant and lactating women, food distribution (among the Kalahari, young men can eat only kidneys, abdominal walls, and genitals), and rules governing courtship, marriage, and war.

To be sure, Boyd acknowledges, maladaptive behavior and false beliefs can spread as well. The Gebusi in Papua New Guinea, for example, attribute all deaths to sorcery, hold inquests, and execute those who are found guilty. And bad outcomes may result “if environmental conditions change and causal principles are violated.” That said, Boyd insists that cultural group selection has allowed human beings to do what other creatures have not done: spread across the globe by creating “successful” local adaptations “that are beyond the inventive capacity of individuals.”

Boyd’s interlocutors agree that collective intelligence, passed across many generations, helps explain the extraordinary ecological success of human beings. Their critiques also help refine Boyd’s theory, and may set some limits on its impact. In his response, for example, Boyd acknowledges that cognitive intelligence and cultural group selection are “mutually reinforcing.” He agrees that people often disagree about what the norms are, whether they have been violated, and that cooperative behavior varies with populations. And Boyd indicates that informally enforced norms tend to work in forager tribes and small horticultural villages, but are much less successful in large, heterogeneous societies.

Boyd, I should add, gives as good as he gets. With an endorsement of more empirical tests, he concludes that “in the end, all of us will be wrong about much of what we believe about cultural evolution, but substantive debates are the means for making progress.”