Throughout most of evolutionary history, sex was just sex. Among vertebrates, fish were the first to do it, going back some 400 million years. While it might be fun for fish and all the other species that evolved to reproduce sexually,
Throughout most of evolutionary history, sex was just sex. Among vertebrates, fish were the first to do it, going back some 400 million years. While it might be fun for fish and all the other species that evolved to reproduce sexually, for most species, sex still is just sex. But for our own peculiar species of primate, sex is about something more. Sex is about babymaking. Contemplating sex and where we come from has played a fundamental role in human mating, partnering and raising children, and in forming families, communities and alliances, and more. Recognising this fundamental difference between us and the rest of Earth’s sexual beings overturns conventional evolutionary thinking, which has long understood human sex, reproduction and kinship as fundamentally the same for us as for any other mammal.
All sexually reproducing animals have a powerful ‘sex drive’. If they didn’t, they would quickly become extinct. Among most animals, this drive demands immediate attention. It’s the yowls of the tomcats in the alley who detect a female in heat, the bawling bull who smells a receptive cow. It can’t be ignored. But it’s not a ‘baby drive’ – at least it isn’t experienced as one. We know the two are intimately related, but the tomcat doesn’t. He just wants to find that female in heat. Sex can certainly make for high drama among manipulative social mammals, especially primates. Among many monkeys and apes, the alpha male often sires the most offspring during his tenure because he is granted the least fettered access to fertile females, and can foil the sexual devices of subordinates. But with our inventions of virgin worship, marriage, castration, contraception, fertility technology and genetic engineering, the human primate experiences sex in an entirely different way from any other animal, enmeshed in all kinds of cultural and emotional networks and significance.
Stories about what make humans unique glorify dexterous fingers, inventive minds and our habit of sharing complex ideas through intricate verbal cues. Our ancestors’ fabled intellects gave rise to art, technology and dynamic, large-scale politics. But there is an oft-overlooked plot in the human saga. It stars the ancient hominins who realised that they’re related to some people and not others, and that sexual intercourse might have something to do with that. The effects of this realisation are profound, and deserve some credit for our species’ widespread success on the planet.
Pop culture is obsessed with sex, and science is no different. And for good reason: sex is fundamental to how and whether so much animal evolution happens. In conventional evolutionary science, ‘favoured’ genes cause themselves to be passed from one generation to the next, because they are responsible for traits that confer reproductive advantages in a particular environment. This is natural selection. When it comes to sex and reproduction, science takes a particular interest in sexual selection: that is, the evolution of traits involving mate choice and mating behaviours. Within this frame, scientists have tried to trace the origins of human mating, marriage and kinship to evolutionary ‘strategies’ that, conscious or not, were responsible for our survival and continued evolution rather than our extinction.
In other words, if you follow this mainstream or ‘Darwinian’ logic, there must be genes that underpin mating behaviours, which in turn cause animals (including the human animal) to be successful in reproducing, and thus those genes (and their associated behaviours) are perpetuated in populations. If that’s how simply things actually happen in nature, there will be genes ‘for’ mate preference, genes ‘for’ pair-bonding, genes ‘for’ polygamy and so on.
We share many genes even with fruit flies, but we share far more with non-human primates. We share an especially large proportion of our genome with our closest relatives – chimpanzees and bonobos – so, if their mating behaviour is genetically driven, then we’ll learn a lot about ourselves by studying these apes. Although no one has actually identified genes for infanticide or for avoiding incest, for most evolutionary scientists, answers to questions such as why is infanticide so common among chimps and some monkeys, or why is the incest taboo so common in human societies, ought to be applicable interchangeably to all of us primates. Thus, evolutionary psychology and evolutionary theory more broadly has a clear theoretical box for human sexuality: the model of animal mating.
Back in 1997, the psychologist Steven Pinker wrote in How the Mind Works: ‘The human mating system is not like any other animal’s. But that does not mean it escapes the laws governing mating systems, which have been documented in hundreds of species.’ In Mutants (2004), the evolutionary developmental biologist Armand Leroi summed up this hardline argument with: ‘the psychologies of pheasants and Fijians are really much the same’. The idea here, the ‘law’ that governs mating, is that sexual selection is as