Illustrations

GEOFFREY MILLER is a man with a theory that, if true, will change the way people think about themselves. His idea is that the human brain is the anthropoid equivalent of the peacock's tail. In other words, it is an organ designed to attract the opposite sex. Of course, brains have many other functions, and the human brain shares those with the brains of other animals. But Dr Miller, who works at the University of New Mexico, thinks that mental processes which are uniquely human, such as language and the ability to make complicated artefacts, evolved originally for sexual display.

One important difference between peacocks' tails and human minds, of course, is that the peahen's accoutrement is a drab affair. No one could say the same of the human female psyche. That, Dr Miller believes, is because people, unlike peafowl, bring up their offspring in families where both sexes are involved in parenting. It thus behoves a man to be as careful about choosing his wife as a woman is about choosing her husband.

Both sexes, therefore, have reason to show off. But men and women will have different criteria for making their choices, and so the sexual-display sides of their minds may differ in detail.

Testing this hypothesis will be a long haul. But in a paper he has just published in the Journal of Personality and Social Psychology, in collaboration with Vladas Griskevicius of Arizona State University, Dr Miller goes some way towards it. He, Dr Griskevicius and their colleagues look into two activities—conspicuous consumption and altruism towards strangers—to see if these support the “mating mind” hypothesis, as Dr Miller has dubbed his idea. Their conclusion is that they do.

Things are seldom what they seem

Altruism, according to the text books, has two forms. One is known technically as kin selection, and familiarly as nepotism. This spreads an individual's genes collaterally, rather than directly, but is otherwise similar to his helping his own offspring. The second form is reciprocal altruism, or “you scratch my back and I'll scratch yours”. It relies on trust, and a good memory for favours given and received, but is otherwise not much different from simultaneous collaboration (such as a wolf pack hunting) in that the benefit exceeds the cost for all parties involved.

Humans, however, show a third sort of altruism—one that has no obvious pay-off. This is altruism towards strangers, for example, charity. That may enhance reputation. But how does an enhanced reputation weigh in the Darwinian balance?

To investigate this question, the researchers made an interesting link. At first sight, helping charities looks to be at the opposite end of the selfishness spectrum from conspicuous consumption. Yet they have something in common: both involve the profligate deployment of resources.

That is characteristic of the consequences of sexual selection. An individual shows he (or she) has resources to burn—whether those are biochemical reserves, time or, in the human instance, money—by using them to make costly signals. That demonstrates underlying fitness of the sort favoured by evolution. Viewed this way, both conspicuous consumption and what the researchers call “blatant benevolence” are costly signals. And since they are behaviours rather than structures, and thus controlled by the brain, they may be part of the mating mind.

There is, of course, a lot of evidence for the first part of this conjecture. Everybody knows that fast cars attract fast women. The second, though, may come as a surprise. So the team did an experiment to compare them.

They divided a bunch of volunteers into two groups. Those in one were put into what the researchers hoped would be a “romantic mindset” by being shown pictures of attractive members of the opposite sex. They were each asked to write a description of a perfect date with one of these people. The unlucky members of the other group were shown pictures of buildings and told to write about the weather.

The participants were then asked two things. The first was to imagine they had $5,000 in the bank. They could spend part or all of it on various luxury items such as a new car, a dinner party at a restaurant or a holiday in Europe. They were also asked what fraction of a hypothetical 60 hours of leisure time during the course of a month they would devote to volunteer work.

The results were just what the researchers hoped for. In the romantically primed group, the men went wild with the Monopoly money. Conversely, the women volunteered their lives away. Those women continued, however, to be skinflints, and the men remained callously indifferent to those less fortunate than themselves. Meanwhile, in the other group there was little inclination either to profligate spending or to good works. Based on this result, it looks as though the sexes do, indeed, have different strategies for showing off. Moreover, they do not waste their resources by behaving like that all the time. Only when it counts sexually are men profligate and women helpful.

That result was confirmed by the second experiment which, instead of looking at the amount of spending and volunteering, looked at how conspicuous it was. After all, there is little point in producing a costly signal if no one sees it.

As predicted, romantically primed men wanted to buy items that they could wear or drive, rather than things to be kept at home. Their motive, therefore, was not mere acquisitiveness. Similarly, romantically primed women volunteered for activities such as working in a shelter for the homeless, rather than spending an afternoon alone picking up rubbish in a park. For both sexes, however, those in an unromantic mood were indifferent to the public visibility of their choices.

These two studies support the idea, familiar from everyday life, that what women want in a partner is material support while men require self-sacrifice. Conspicuous consumption allows men to demonstrate the former. Blatant benevolence allows women to demonstrate the latter. There is, however, a confounding observation. The most blatant benevolence of all, that of billionaires giving away their fortunes and heroes giving away (or at least risking) their lives, is almost entirely a male phenomenon.

To examine this, the team did another experiment. They found that when requests for benevolence were financial, rather than time-consuming, romantically primed men were happy to chip in extravagantly. Giving money to charity is thus more akin to conspicuous consumption than it is to blatant benevolence. The primed men were also willing (or at least said they were willing) to act heroically as well as spend—but only if the action suggested was life-threatening. Women, romantically primed or not, weren't.

Heroism, of course, is a pretty high-risk strategy. But if you survive, you really have proved the quality of your genes. As the old saw has it, faint heart never won fair lady. On the other hand a soft heart, it appears, wins a gentleman.