I\'m an expert. Many of us are. My first wife never said the word \"love\" without a sneer; my present wife is a true believer. So I\'ve looked at love from both sides now. But if Robin Dunbar is to be believed, I really don\'t know love at all. Remember those PG Tips ads where they dressed chimpanzees as human beings and made them drink tea? This book is rather like those ads in that it confuses the animal and the specifically human. Why do we kiss, it asks. To taste our potential partner\'s saliva and decide if they are healthy enough to breed with, a bit like dogs sniffing at each other. A bad taste, a bad smell and off we go with someone else. Sometimes the truth is disturbing, but is this really why my wife and I are still kissing after all these years? It seems to me more like a way of having sex with our mouths – which is wonderful if you like sex, and disgusting if you don\'t. It certainly isn\'t something a dog would do. 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. Dunbar thinks dreams and fantasies only get in the way. He discusses them in the contexts of women being ripped off by gigolos, of mystics who believe they have been ravished by God, of de Clérambault\'s syndrome (erotomania). In other words, he\'s a cynic, even though he knows that the most successful marriages are the ones where the partners idealise each other. He discovers that our sexual partners tend to resemble our parent of the opposite sex and he describes this as a curiosity – it never occurs to him the Oedipus complex might be at work. The idea that we are different from marmosets because we idealise and fantasise, because we kiss and laugh, read poetry and sing songs, because we are wonderfully good at displacing our reproductive drives into all sorts of other activities, is beyond him. American generals, Dunbar tells us, have had fewer children than middle-ranking officers. \"It was as though they overdid themselves and went too far\", is all he can say, because naturally their real goal was not status but the replication of their genes. They had failed the only test that counts. \"From a strictly biological point of view,\" says Dunbar, \"relationships exist to facilitate reproduction.\" Until the 1960s the French-speaking population of Québec was very good at reproduction, with each woman producing an average of four children. Then along came contraception – they stopped going to church and each woman had on average only 1.5 children. Relationships no longer existed primarily to facilitate reproduction. Biology had been trumped by the desire for an improved standard of living. Instead of having children, the Québecois had cars, central heating and holidays in Florida. Dunbar has nothing helpful to say about non-reproductive sex – about contraception, or homosexuality, or even masturbation. He has little to say about happiness, and nothing at all to say about pleasure. He prefers to talk about the relative length of our second and fourth fingers: a high 2D:4D ratio implies high levels of testosterone and so polygamy or promiscuity, while a low 2D:4D ratio implies marmoset love. Hence we can determine the family structure of Neanderthals by measuring their finger lengths. Maybe. This basic confusion between humans and animals isn\'t the only problem with Dunbar\'s work. He loves neuro-imaging. If you give psychopaths various simple tests, different bits of their brains light up from those that light up in the rest of the population. Consequently \"psychopaths are born and not made by circumstance.\" But Dunbar also tells us about London taxi drivers. They have large hippocampuses – the bit of the brain that deals with orientation. At first it seemed that people with big hippocampuses become taxi drivers; but further research established that doing \"the knowledge\" (studying to become a London taxi driver) causes your hippocampus to grow. Mind/body interactions go both ways: the fact that psychopaths\' brains are different doesn\'t prove that psychopaths are born and not made – it would seem perfectly plausible that some are born, some are made, and often it\'s a bit of both. In the end, what Dunbar offers is a Darwinian reworking of traditional sexual stereotypes. We would have to put up with this if the arguments were robust, but they aren\'t. Where he is good, surprisingly, is on intimacy, friendship and family. Lovers who touch each other a lot have lower cortisol levels – they are less stressed. People in loving relationships have a higher pain threshold. Laughter shared between friends is so powerful that three letters in a text message – LOL – can make us happy. Experimental evidence really does seem to show that people trust their family more than they trust their friends, and that they will make sacrifices for their family that they would not make for their friends – since this is often a terrible mistake it is hard not to think that this has something to do with sharing genes in common. Dogs can count as people where friendships are concerned. We aren\'t wired up to have lots of friends (Facebook notwithstanding), and one lover is worth two friends – so people who fall in love drop two of their close friends. Women like talking while men like doing things together – the average phone call involving a male lasts 7.3 seconds. When Dunbar is talking about friendship he doesn\'t feel the need to look for comparisons with other species – voles (nearly all promiscuous) and the bee-eater bird (like marmosets, they have \"an almost identical social arrangement to humans\") disappear from the story. For what makes friendship possible is the development of \"theory of mind\" – \"the capacity to understand what another person is thinking\" – and this is unique to humans. Indeed we only begin to develop it after the age of five, and go on developing it until the mid-20s. Without it we would be unable to engage in pretend play or lying. Even our laughter is different from that of the apes. Strangely, he doesn\'t say that without empathy there would be neither love nor betrayal. So here\'s the puzzle: Dunbar understands there is something uniquely human about friendship, but not about love. Because lovers make babies he thinks they are just like marmosets. What Dunbar needs is a better theory of mind. Don\'t misunderstand me: of course we are naked apes. Evolution made us – up to a point. Evolution gave us a capacity for loving and lying, for sympathy and cruelty, for displacement. But, like the taxi drivers with the enlarged hippocampuses, we have, for better or worse, remade ourselves. One thing is clear: love is never natural. Just as we learn language from those around us, so we learn love – if we are lucky, that is.