From The Guardian:
Dunbar believes emotions such as love and social institutions such as marriage are strategies to maximise the reproduction of our genes. In biological terms, the most successful of all humans has been Genghis Khan – around 0.5% of all males alive today are descended from him and his brothers. But the Great Khan's reproductive strategy of mass rape is something of an aberration. Modern societies derive from communities of hunter-gatherers who practised serial monogamy. Love and marriage are the emotional and social expressions of a reproductive strategy that goes back 200,000 years or so. Why do we pair up? Not so that men can help feed and raise children – women would do this better on their own (the time men spent hunting was largely time wasted, unlike the time women spent gathering). Dunbar runs through a range of biological comparisons – wolves (“resolutely monogamous”, but male wolves vomit up food for the mother and pups; unlike many human males they really are good dads), goats, baboons, gorillas – and concludes that we are like marmosets. Women need husbands to protect them from being attacked by other men. Men don't get much out of love and marriage (except, of course, the reproduction of their genes); women get security. But women don't just want security. According to Dunbar (who doesn't see that this is a major hole in his argument), all women would have needed to do is gang together into large groups in order to defend themselves. If only they had kicked out the worthless hunters, who didn't catch enough to feed themselves, let alone anyone else, and only chased big game to show off, they could have managed perfectly well. Why are there no societies of vegetarian Amazons? Presumably because big-game hunting was a useful way of testing men's fitness for reproduction. So love and marriage are the result of a complicated trade off between safe sex and exciting sex. We are marmosets who dream of being gorillas.
More here.