How Many Friends Does One Person Need? (27 page)

Saliva is full of chemicals exuded by the body, not the least of which are a group of proteins known as MUPs (major urinary proteins). OK, this doesn’t sound so good. But before you panic, the name comes from the fact that MUPs were first identified in rodent urine, where they
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seem to have a lot to do with individual recognition and territorial behaviour. Jane Hurst and her colleagues at Liverpool University have recently shown that female mice can discriminate between males solely on the basis of differences in their MUPs. MUPs occur in urine simply because urine is a very convenient mechanism for animals to deposit signals of their presence in an area. They also probably occur pretty much everywhere that you care to excrete bodily fluids of any kind.

So, the next time you get in a deep clinch, you might pause and remind yourself that this is all about choosing the right mate with a good set of immune responses to complement your own and that MUPs are the route to success... On second thoughts, perhaps you should just shut down your busy conscious mind and let your subconscious take over so that nature can take its course. Evolution did not spend many millions of years perfecting a mechanism of mate choice only to have you mess it up by thinking too much about it.

Now, if there is one thing everyone knows about Eskimos, it’s that, instead of shaking hands, they rub noses when they greet each other. Well, actually, that’s a bit of a myth created by European explorers when they first came across the Eskimos. In fact, they place their noses next to each other’s faces and breathe in deeply. Nor are they the only people to do this. The Maoris in New Zealand also rub noses when they meet, a behaviour known as
hongi
. Theirs too is less of a rub and more of a light press of one nose upon another in a symbolic joining together of host and visitor.
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What these folks are in fact doing is breathing in each other’s smell, one of the best markers of who you really are. In our vision-dominated world, we often forget just how important smell is to us. In fact, we use smell a great deal more than we realise – and nowhere more so than in the business of mate choice. Back in the mischievous 1960s, some experimenters sprayed androstenone (one of a family of steroids that are a natural by-product of testosterone, the so-called male hormone – it’s responsible for the slightly musty smell that aftershave-less men often have) around some of the cubicles in men’s and women’s public toilets. Then they sat back and watched. What they found was that men avoided the ‘androstenoned’ cubicles – having ventured in, they would usually back out hastily and find an androstenone-free one instead. But women made a bee-line for the androstenoned cubicles.

In an updated version of that experiment, Tamsin Saxton and her colleagues at Liverpool University applied androstadienone (another of the same family of steroids) to the upper lips of women at a speed-dating event. In a speed-dating event (for those of you who have yet to experience this curious form of mating market for the ultra-busy), the girls sit round the room at tables and the boys spend five minutes in a brief conversation with each one in turn, in a kind of gigantic round-robin. At the end of the evening, each person lists the names of the people they would like to meet again, and the organisers then exchange details for those who express an interest in meeting each other. It’s a perfect setting for an experiment in which each sex can have a brief taste of a dozen or so possible mates and hopefully choose the most congenial.

In this study, the androstadienone was concealed in
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clove oil to disguise it, which also made it possible to control for the effects of other odours. So a third of the women had androstadienone-plus-clove-oil, another third had just clove oil and the final third had plain water. That way, it was possible to separate out clearly the effect of the clove oil substrate from the smell itself.

The results were spectacular. The women who had received the androstadienone not only rated the men they met at the speed-dating event as more attractive than the women in the other two groups, but they were also significantly more likely to ask to see them again. Somehow, the androstadienone acts on a deeply buried brain mechanism to precipitate a rosier-than-reality view of the hulking brute that stands before you. Who said romance was dead?

Still, when all else fails, guys, there is one way to improve your chances. Become a hero. Some years ago, Sue Kelly, then one of my students, ran an experiment in which she offered women a series of vignettes of men with a range of different traits. Some were boringly steady with humdrum jobs, some worked in caring professions, others were risk-takers. The women were asked to rate each individual for their attractiveness as a friend, a long-term partner or a prospect for a one-night stand. The caring altruists got top marks as long-term partners, but the risk-takers swept the board as partners for one-night stands. They were simply rated as much more attractive. William Farthing of the University of Maine obtained similar results when he asked women to rate different males for
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attractiveness as mates: they much preferred heroic risk-takers against non-heroic risk-takers, although in both cases they rated those who took medium risks higher than those who took high risks. It seems that, in general, risk-taking is good advertising copy if you are a male, but don’t overdo it: unnecessary stupidity carries a premium.

So do men take more risks than women? The answer, in general, is yes. And we found evidence of this when we carried out a study at a zebra crossing at a busy city-cen-tre junction. In general, men took higher risks than women – in other words, they were more likely to cross the road when a car was approaching the crossing and the lights were on green for the car than women were. More importantly in the present context, they were much more likely to do this if there were women present as an audience than if there were not.

Is this because men realise that women are attracted by risk-taking behaviour? The answer seems to be that men are quite good at identifying the things that press women’s mate-choice buttons. In her study, Sue Kelly wanted to know whether men understood women’s preferences, and so asked men to rate the same character vignettes from a woman’s point of view. They were pretty good, though they tended to exaggerate women’s actual preferences.

Several recent studies have looked at real-life heroism from an evolutionary point of view. One study examined the records for the Carnegie Medal, a very prestigious national award in the USA given to civilians for unusual courage in emergency situations – for example, rushing into a raging torrent to save someone’s life. The citations for these awards revealed some very striking patterns.

Men were much more likely to rescue (or attempt to res-
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cue) unrelated young women than anyone else, whereas women were disproportionately more likely to rescue related children. In other words, for women acts of heroism are about investment in one’s children, but for men they appear to be more about mating opportunities. Another of my students, Minna Lyons, analysed a large corpus of recent British newspaper accounts where people had attempted to rescue others in distress. Almost all the rescuers were men, but there was an intriguing status bias. Men from the richer end of society rarely acted as heroes; instead, most of the rescuers were from the poorer end of the socio-economic spectrum. Such men, she argued, had more to gain in the mating market from being recognised as heroes.

I found a rather analogous trend among the historical Cheyenne Indians of North America. The Cheyenne had two kinds of chiefs: peace chiefs who inherited their status, never took part in war and married early, and war chiefs who eschewed marriage and led the tribe in war, often staking themselves to the field of battle so as to die rather than be defeated. A war chief might eventually marry, but only if he survived long enough to be able to renounce his war vows with honour. The demographic records from the later nineteenth century show that men from the hereditary class of peace chiefs (the upper tier of society) almost never became war chiefs. Instead, almost all the war chiefs were orphans or the sons of low-born members of the tribe, whose chances of finding a wife were slim at the best because their status made them less than desirable catches. But men who were successful war chiefs – meaning those who survived long enough to be able to retire with honour and rejoin normal society –
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proved to be very attractive. On average, they ended up siring more children than peace chiefs despite having a much shorter married life.

That risk-takers are reproductively more successful seems still to be true, even in the more peaceful environment of modern Britain. Giselle Partridge, then one of my students at Liverpool University, carried out an extensive survey of men’s risk-taking and compared this with the number of children they had during their lifetime. She measured risk-taking both through occupation (firemen, for example, compared to desk-bound administrators) and through a questionnaire on behaviour (convictions for speeding, risky leisure activities). High risk-takers had significantly more children than low risk-takers. While the explanation remains unclear (are high risk-takers more likely to have unprotected sex, or are they just more attractive to women?), the facts speak clearly enough. Men that take risks make a bigger contribution to the next generation.

You pays your money, and you takes your choice.
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Some years ago, my former colleague Sandy Harcourt, now at the University of California at Davis, showed that primates which mated monogamously had much smaller testes for body weight than species that mated promiscuously. To evolutionary biologists, the explanation was obvious. In promiscuous mating systems, males can never be sure that they will be the one who is mating with a female at the time she ovulates and an egg is available for fertilising. In such cases, the best way to maximise the chances of fertilising the female is to leave her with as much sperm as you can possibly muster in order to swamp the sperm of any other males that have previously mated with her, or might mate with her in the next few days during her fertilisation window. To achieve that, it is necessary to have large testes capable of producing excess quantities of sperm. The great quandary for us is that when Harcourt and his colleagues plotted humans on the graph, they fell exactly halfway between the two groups – we are neither wholly monogamous nor wholly promiscuous. So are we monogamous or promiscuous by nature?
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With these words, Christianity has traditionally enshrined the idea that humans are a monogamous species. So why do more than a third of all marriages in Britain and half of those in the US end in divorce? And how come as many as fifteen per cent of children are not the biological offspring of their registered father? Some people see this as a sign of the times: a breakdown in family values, the dis-integration of society, or a modern disease that requires everything, including relationships, to be ‘new and improved’. In recent years biologists have come up with another explanation. They have been finding that monogamy is not a fixed and immutable instinct, hardwired into an animal’s brain. Even creatures once considered as paragons of fidelity will indulge in a fling, if the situation is right.

Take the South American marmoset and tamarin monkeys. Both are usually monogamous in the wild, with males largely responsible for bringing up the young. But in some cases, males engage in roving polygamy, hitching up with a succession of females. ‘Divorce’ rates can be as high as a quarter to a third of all pairs in the population during any one year. This radical change in behaviour is often prompted by an excess of males, usually because of high female mortality. With females in short supply, males who cannot get a mate become ‘helpers-at-the-nest’, willing to assist with the rearing of offspring that are not their own. The presence of a helper increases the chances that a breeding male will desert his partner and go searching for another female, because he will be able to breed again sooner than if he waits for his current mate to come back
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into breeding condition. The helper gets his payoff next time the female comes into oestrus, when he has his turn to mate with her. And the females seem indifferent to their mate’s behaviour: so long as they have a male to help with rearing the offspring, they don’t seem to mind too much who that male is.

Breeding males who are powerful enough to pursue this kind of roving strategy can gain up to twice as many offspring as they would by remaining in a normal monogamous relationship. Females fare no better or worse, while the helpers make the best of a bad situation. In other words, flexible behaviour patterns allow the breeding males to exploit the shortage of females to increase their reproductive success. In this case, the new behaviour is a response to a change in circumstances. But even without external changes, it may be in the interests of monogamists to adopt a more flexible approach. The animal world, it turns out, is full of examples of cuckoldry, cheating and even divorce, by supposedly lifelong mates as they try to overcome what I call the monogamist’s dilemma.

Monogamy is relatively rare among mammals. Only about five per cent of mammals are monogamous, with primates and the dog family (wolves, jackals, foxes etc) favouring the practice more than most. But there is one group of animals for which monogamy is the rule. Around ninety per cent of bird species pair, at least for a given breeding season. On the surface, it looks like true wedded bliss. But a decade or so ago, that illusion was blown away when the new technology of DNA fingerprinting revealed that as many as a fifth of the eggs produced by supposedly monogamous female birds had not been sired by their regular partners. Many male birds were busily
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feeding offspring that were not their own.