ABSTRACT
Darwin’s idea of natural selection was that animals should end up with physical and behavioural characteristics that allow them to perform well in the ordinary processes of life such as competing with their rivals, finding food, avoiding predators and finding a mate. Most features of plants and animals should, therefore, have some adaptive function in the struggle for existence. As noted earlier in relation to Figure 1.1, the life and death of thousands of our ancestors should have ensured that by now our characteristics are finely tuned to growth, survival and reproduction. Nature should allow no extravagance or waste. So what about, for example, the spectacular train of the peacock? It does not help a peacock fly any faster or better. Neither is it used to fight rivals or deter predators-in fact, the main predator of peafowl, the tiger, seems particularly adept at pulling down peacocks by their tails. It would seem
Natural selection and sexual selection compared
to be an irrelevance, a magnificent one to be sure, but nevertheless an encumbrance that should have been eliminated by natural selection long before now. Nor is the peacock’s tail an exception: many species of animals are characterised by one sex (usually the male) possessing some colourful adornment that serves no apparent function (or even seems dysfunctional), while the other sex, like the peahen, seems much more sensibly designed. Such features seem, at first glance, to challenge the power of natural selection to explain the behaviour of animals.
