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Charles Darwin and Stanford biologist Joan Roughgarden have three things in common: a fascination with barnacles, a passionate desire to understand evolution, and a knack for controversy. While writing Evolution’s Rainbow a few years ago, Roughgarden concluded that the astonishing diversity of sexual types and interactions meant that Darwin’s theory of sexual selection (based on competitive males and choosy females) was not just wrong, but unfixable. She wants to replace it with social selection, in which a wide variety of social interactions, say, same-sex bonding and group membership, determine an animal’s reproductive success and therefore shape bodies and behaviours.…