Nicholas Wade in The New York Times:
Nature is reputed to be red in tooth and claw, but many arms races across the animal kingdom are characterized by restraint rather than carnage. Competition among males is often expressed in the form of elaborate weapons made of bone, horn or chitin. The weapons often start off small and then, under the pressure of competition, may evolve to attain gigantic proportions. The Irish elk, now extinct, had antlers with a span of 12 feet. The drawback of this magnificent adornment, though, was that the poor beast had to carry more than 80 pounds of bone on its head.
In a new review of sexual selection, a special form of natural selection that leads to outlandish armament and decoration, Douglas J. Emlen, a biologist at the University of Montana, has assembled ideas on the evolutionary forces that have made animal weapons so diverse. Sexual selection was Darwin’s solution to a problem posed by the cumbersome weapons sported by many species, and the baroque ornaments developed by others. They seemed positive handicaps in the struggle for survival, and therefore contrary to his theory of natural selection. To account for these extravagances, Darwin proposed that both armaments and ornaments must have been shaped by competition for mates.