George C. Williams

George C. Williams (1926–2010) was an American evolutionary biologist whose 1966 book Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought delivered the decisive critique against group selection and established the gene-centered view of evolution as the dominant framework in evolutionary biology for three decades. Williams argued that adaptations are almost always properties of individual organisms, not of groups, and that invoking group-level benefits to explain individual traits is a violation of parsimony — what he called "clumsy, unparsimonious, and fundamentally flawed" reasoning. His critique was so devastating that "group selection" became a term of intellectual contempt for a generation of biologists.

Williams's argument was mathematical and operational. He showed that group selection requires conditions that are rarely met in nature: groups must be small, isolated, and subject to frequent extinction; genetic variation among groups must exceed variation within groups; and individual selection against the altruistic trait must be weak. In most natural populations, gene flow homogenizes groups, and individual selection against altruism is strong. Williams therefore concluded that group selection is negligible as an evolutionary force and that all apparent altruism can be explained by kin selection, reciprocal altruism, or individual benefit.

The irony of Williams's legacy is that his mathematical framework — the very rigor that made group selection seem impossible — was later used by David Sloan Wilson to show that group selection is not only possible but mathematically guaranteed under certain population structures. Williams's conditions were precise enough to become the conditions for Wilson's revival. The critique and the revival are not enemies; they are successive approximations of the same truth, seen from different scales.

Williams was right that most group selection arguments were sloppy. But he was wrong that the sloppiness meant the phenomenon was negligible. His parsimony principle — never invoke a higher-level explanation when a lower-level one will do — is a heuristic, not a law. And heuristics fail when the system is genuinely multi-level. Williams's lasting contribution was not the elimination of group selection but the establishment of rigorous standards for claiming it. In that sense, he was the father of the modern revival he opposed.