Art for partners' sake

Dylan Evans discovers the scientific rules of sexual attraction

Saturday May 6, 2000
The Guardian

Promiscuity
Tim Birkhead
Faber, £9.99, 256pp

The Mating Mind
Geoffrey Miller
Heinemann, £20, 528pp

Everyone has heard of natural selection, but how many know about Darwin's other dangerous idea - the theory of sexual selection? He wrote a book about it in 1872, but the idea fell on deaf ears. Nowadays it is one of the hottest areas of research in evolutionary biology, as two new books make clear. Promiscuity by Tim Birkhead and The Mating Mind by Geoffrey Miller both explore the effects of sexual selection, though in rather different ways.

Tim Birkhead, professor of behaviour and ecology at Sheffield University, has spent many years researching the reproductive biology of birds - which is what prompted Darwin to develop the theory of sexual selection in the first place. Darwin was particularly troubled by the peacock, whose exuberant tail appeared to flaunt the logic of natural selection. Not only do big, bright tails seem biologically useless, they can be detrimental to the owner's health, attracting predators and making it harder to escape. It seems that such ornaments should not evolve, and yet nature is full of them, from monkeys with red and white faces to beetles with carapaces of gold and sapphire.

Darwin solved this riddle by proposing that animal ornamentation evolved to attract sexual partners. If peahens prefer to mate with those peacocks who have the biggest, brightest tails, then the peacocks with tiny drab ones won't pass on the genes for such tails. From the gene's point of view, if you fail to produce any offspring, it doesn't matter how long you survive; your genes die with you.

As the example of the peacock shows, sexual selection is usually about male competition and female choice. If natural selection is a blind watchmaker, sexual selection is a keen-eyed judge at a beauty contest in which the competitors are usually males. Darwinians are often accused of promoting an androcentric view of sexuality, but the theory of sexual selection tells a different story. Rather than viewing females as mere portable wombs, sexual selection theory portrays them as cunning sexual strategists.

In Promiscuity, Tim Birkhead argues that male competition and female choice do not stop at the moment of copulation but continues right up to fertilisation, though in the post-coital stage the competitors are no longer males but their sperm.

When a female has sex with more than one male during the same fertile period, the sperm from her various partners battle it out inside her reproductive tract for the right to fertilise her eggs. Female choice continues to operate inside the female body, as sperm from one partner may be preferred over the sperm from the others.

Birkhead illuminates the murky world of sperm competition with a stunning variety of examples: from the catfish who get pregnant by giving their partners blowjobs to the insects who take cradle-snatching to an extreme by inseminating females before they emerge from their pupal shrouds, the reader is treated to a veritable cook's tour of reproductive biology.

If there is one consistent theme to emerge from this bizarre variety, it is that female sexual fidelity is extremely rare in nature. For a long time biologists assumed that promiscuity was a predominantly masculine trait; the research on sperm competition has changed all this. As Birkhead points out, sperm competition would not exist in a species unless the females typically mate with multiple partners during the same fertile period. Biologists have thus been forced to abandon their belief in the myth of the monogamous female.

The Mating Mind is also about sexual selection, but differs from Promiscuity in two important ways. First, while Birkhead writes about a whole variety of organisms, Miller focuses exclusively on just one species - a rather curious bipedal ape known as Homo sapiens. Second, whereas Birkhead sets out the consequences of sexual selection for anatomy and behaviour, Miller explores the effects of sexual selection on the mind.

Put these two points together and you get a provocative thesis: the most distinctively human aspects of our minds evolved not by natural selection but by sexual selection. The things we think of as most "human", such as our capacities for art, morality and language, Miller argues, did not evolve because they provided any survival benefit, but rather because they helped our ancestors to seduce their lovers. Art and creativity are not survival gadgets but courtship devices.

Miller is an evolutionary psychologist, but his views on mental evolution are rather different from those of his Darwinian colleagues. Most evolutionary psychologists have adopted a "survivalist" view of evolution that neglects the importance of sexual selection. Steven Pinker, for example, thinks that art and creativity are mere by-products of mental capacities that evolved for more practical purposes. In his book How the Mind Works, art, morality and creativity were relegated to a speculative final chapter. To many people, including Miller, this renders evolutionary psychology rather unsatisfying. The human mind may well consist mainly of basic mechanisms for things like vision and locomotion, while morality and art may be mere icing on the cake, yet it is the icing we really care about.

In Miller's book, the icing is the point: language, art and morality are presented as adaptations designed for sexual ends. But before you shout "reductionist", remember that sexual selection is driven by mate choice: minds take centre stage in evolution. Miller does not want to reduce psychology to biology; on the contrary, he sees psychology as a powerful force in shaping biology. The reason we possess the capacity to tell jokes and compose symphonies is, he claims, because our ancestors preferred funny, creative partners to dull ones. What emerges is a vision of the Stone Age in which love was just as important, and almost as complex, as it is today. Miller argues persuasively that this is "probably the least reductionistic theory of the mind's evolution one could hope for that is consistent with modern biology".

In suggesting that our artistic capacities function as sexual adverts, Miller is not suggesting that all art is motivated by some unconscious wish to have sex. Just as a peacock does not need to sublimate his libido to grow a pretty tail, so our capacity for art can be a sexual display without any dark Freudian motives to underlie it. All that is needed for Miller's theory to work is that our ancestors preferred to mate with artistic partners.

We then need to explain why they had this preference, but Miller has an answer for this too. He argues that works of art have, until very recently, been very reliable indicators of the artist's fitness. To produce a beautiful object such as a statuette or, indeed, a handaxe required dexterity, strength, good eyesight, careful planning and patience. The preference for mating with good artists evolved by piggy-backing on the good genes that children would inherit from artistic parents.

Nowadays, of course, things are very different. Machines can turn out thousands of perfect objets d'art much more quickly and efficiently than any human being, so qualities such as symmetry and intricate detail no longer serve as reliable indicators of artistic talent. Thankfully, however, there are still some things that machines cannot do as well as humans, such as write fascinating books like these two. Language still provides humans with a wonderfully reliable way to show off their biological fitness. If we judge these books by the theory Miller propounds, both he and Birkhead should be very pleased with themselves: their peacock's tails should attract a lot of admirers indeed.