Animal attraction.

From fruit flies to elephants, females pick the male with which they want to mate. The males, in turn, compete with each other to get a female's attention, each vying to show her that he will be the best sperm donor for her babies. That is why, evolutionary biologists say, males are most often the ornamented sex. Charles Darwin was the first scientist to devise a theory of sexual selection and to recognize that females frequently select mates. He began to develop the notion while writing 'On the Origin of Species,' in which he argued that the related theory of natural selection is the primary force in the evolution of all organisms. Natural selection goes far in explaining why one individual animal survives to pass on its genes to the next generation, while another dies leaving no descendants.