Every summer, the peacocks that roam free within Whipsnade Wild Animal Park in Bedfordshir

e expose their 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 collaborator, Alfred Russel Wallace, though in many ways more "romantic" than Darwin, was in others even more Darwinian. "Beauty for beauty's sake" he wanted nothing of. If peahens chose cocks with the showiest trains, he felt, then it must be that they knew what they were about. The cocks must have some other quality, which was not necessarily obvious to the human observer, but which the hens themselves could appreciate. According to Wallace, then, the train was not an end in itself, but an advertisement for some genuine contribution to survival.

Now, 100 years later, the wrangle is still unresolved, for the natural behavior. of peafowl is much harder to study than might be imagined. But 200 birds at Whipsnade, which live like wild birds yet are used to human beings, offer unique opportunities for study. Marion Petrie and her colleagues at Whipsnade have identified two main questions. First, is the premise correct—do peahens really choose the males with the showiest trains？ And, secondly, do the peacocks with the showiest trains have some extra, genuinely advantageous quality, as Wallace supposed, or is it really all show, as Darwin felt？

In practice, the mature cocks display in groups at a number of sites around Whipsnade, and the hens judge one against the other. Long observation from hides, backed up by photographs, suggests that the hens really do like the showiest males. What seems to count is the number of eye, spots on the train, which is related to its length; the cocks with the most eye-spots do indeed attract the most mates.

But whether the males with the best trains are also "better" in other ways remains to be pinned down. William Hamilton of Oxford University has put forward the hypothesis that showy male birds in general, of whatever species, are the most parasite free, and that their plumage advertises their disease-free state. There is evidence that this is so in other birds. But Dr. Petrie and her colleagues have not been able to assess the internal parasites in the Whipsnade peacocks to test this hypothesis. This year, however, she is comparing the offspring of cocks that have in the past proved attractive to hens with the offspring of cocks that hens find unattractive. Do the children of the attractive cocks grow faster？ Are they more healthy？ If so, then the females' choice will be seen to be utilitarian after all, just as Wallace predicted.

There is a final twist to this continuing story. The great mathematician and biologist R.A. Fisher in the thirties propos

A．To show that a peacock's train serves no useful purpose.

B．To solve a problem that Charles Darwin could not solve.

C．To compare peacocks in the wild with those in captivity.

D．To demonstrate that Charles Darwin's theory was wrong.