Every summer, the peacocks that roam free within Whipsnade Wild Animal Park in Bedfordshire their expose magnificent trains to the critical and often disdainful gaze of the hens. They re-enact the mystery that tormented Charles Darwin to his dying day: how in this competitive world, where nature — as Tennyson said — is red in tooth and claw, could birds have evolved such an obvious extravagance? How do they get away with it? The zoologist Marion Petrie and her colleagues of the Open University are now exploiting the quasi-wild conditions of Whipsnade to try, a century after Darwin's death, to settle the matter. Darwin argued that living creatures came to be the way they are by evolution, rather than by special creation; and that the principal mechanism of evolution was natural selection. That is, in a crowded and hence competitive world, the individuals best suited to the circumstances - the 'fittest' are the most likely to survive and have offspring. But the implication is that fittest would generally mean toughest, swiftest, cleverest, most alert. The peacock's tail, by contrast, was at best a waste of space and in practice a severe encumbrance; and Darwin felt obliged to invoke what he felt was a separate mechanism of evolution, which he called 'sexual selection'. The driving mechanism was simply that females liked in his words 'beauty for beauty's sake'. But Darwin's friend and col laborator, Alfred Russel Wallace, though in many ways more 'romantic' than Darwin, was in others even more Darwinian.