Stone Age Sex


Neil McArthur in Aeon (French actor Alain Delon and Italian actress Claudia Cardinale during a scene from The Centurions 1965. Photo by George Rodger/Magnum):

The roots of evolutionary psychology can be traced back to Charles Darwin himself, who says in On the Origin of Species (1859) that, armed with the theory of natural selection, ‘psychology will be based on a new foundation’. But it truly came into its own in the 1970s, thanks to Robert Trivers, then a Harvard postgraduate, who wrote a series of papers that helped to define evolutionary psychology as a field. One of these, ‘Parental Investment and Sexual Selection’ (1972), laid out the basic elements of an evolutionary explanation for sexual behaviour. Trivers looked at data from a variety of animal species, and concluded: ‘The relative parental investment of the sexes in their young is the key variable controlling the operation of sexual selection. Where one sex in­vests considerably more than the other, members of the latter will compete among themselves to mate with members of the former.’

Trivers’s paper looked only glancingly at human behaviour, though it was rich in suggestions for further research. In his book, The Evolution of Human Sexuality (1979), the anthropologist Donald Symons used Trivers’s basic ideas to explain how people make sexual choices. Symons wanted to know what women and men were after when they went looking for sex, and he arrived at a relatively simple answer: ‘Men like sex with strangers … and women generally don’t.’

Symons was a powerful theoriser, but he had been unable to offer much in the way of actual data. In 1981, an ambitious young Harvard professor, David Buss, read Symons’s book, and decided to look for hard evidence to test its key claims. Though he started with a survey of a few middle-class white people, he was not content, as many of his followers would later be, to stop there. He assembled a group of international collaborators into what he called the International Mate Selection Project, which asked people from 37 different cultures what they looked for in a sexual partner. His collaborators risked their lives to survey Zulu women in remote South African villages and to smuggle information, carefully coded to avoid government censors, out of Communist China. The results, first published in 1990, provided data from close to 10,000 respondents in 33 countries and they revealed some strikingly consistent patterns across a variety of cultures, all more or less in line with Symons’s predictions. Buss used this data as the basis for what he called ‘sexual strategies theory’.

Though the data from Buss’s surveys confirmed the basic hypotheses of Trivers and Symons, the resulting theory introduced some important refinements. Notably, sexual strategies theory pays attention to an obvious fact that earlier evolutionary psychologists had left largely unanalysed: women sometimes want casual flings, too.

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