Books: Why (Brain) Size Really Matters ; Humans Developed Their Show-Off Skills - from Jokes to Philosophy - to Attract Mates. It's the Survival of the Wittiest, Argues Colin Tudge

Article excerpt

The Mating Mind

by Geoffrey Miller

Heinemann, pounds 20, 537pp

Charles Darwin made not one, but two great contributions to evolutionary theory. The first is the one that everyone thinks they know: the mechanism of "natural selection", leading to what Herbert Spencer called "survival of the fittest". The other is "sexual selection by mate choice", formally proposed in 1871, which says that creatures who reproduce sexually must evolve features to attract mates, for they will not leave offspring unless they do. The two driving forces are largely in conflict, as illustrated by the peacock's tail: wonderful for pulling hens, but potentially disastrous for evading tigers.

But although biologists (and the world at large) embraced natural selection (albeit often in garbled form and with various shades of political overlay), they largely ignored sexual selection for the next 100 years. The business of attracting mates just seemed too frivolous: too effete to compete with the vicissitudes of blood-and- guts survival, so ruthlessly and obviously subject to natural selection.

Sexual selection re-emerged only when a few biologists in the 1980s finally realised the force of what Darwin had said: no mates, no offspring. There is nothing frivolous about mate attraction, even if the features it encourages - feathers and antlers - may be pure caprice. In The Mating Mind, Geoffrey Miller, one of the brightest sparks in modern evolutionary theory, shows how sexual selection might resolve one of the most taxing puzzles of biology: why our own kind of animal, Homo sapiens, is so extraordinarily clever.

The traditional explanation (apart from that of the Book of Genesis) is rooted in natural selection. Big brains and the intelligence that goes with them are obviously useful, the traditionalists say, and are bound to enhance survival. Humans are ground-living apes whose arms and hands are no longer needed for locomotion and so have been freed for making tools.

Ever-more dextrous hands encouraged the selection of bigger brains, and vice versa. By such "co-evolution", the human brain has doubled in size this past two million years, from 700ml to around 1450ml - an unprecedented increase, and miraculous in such a twinkling of biological time.

But there is a snag with this scenario. Dour survival pressure might indeed produce nimble fingers and the ability to count to a dozen or so (if only to keep track of mammoths and rival predators) but modern humans can do much more. Some can do calculus and quantum mechanics. Similarly, we don't just scratch directions on the rocks. A few of us can paint like Titian.

Nor do we simply draw up hunting rosters. We write sonnets. We are not merely agile. We dance like Nureyev, and spin like Comaneci. In short, our palpable abilities far outstrip the requirements of survival on the Pleistocene plains of Africa - so how could they have been shaped by natural selection?

Defenders argue that our present skills are side-effects: evolving the ability to count to 12 we also, somehow, developed the essentials of algebra. Miller's sexual-selection thesis stands in absolute contrast. He proposes that men in particular evolved a phantasmagoria of skills - from high- flown philosophy to break- dancing and fine art - just as peacocks evolved their tails: to show women what fine fellows they are. …