Peacock

In the book’s account of sexual selection, Peacock’s elaborate tail is a costly signal whose waste is the point: it advertises fitness because producing an extravagant display requires resources. The example shows how a trait that may be wasteful for the species can still benefit individuals competing to attract a mate.

The Tail as a Fitness Signal

The book distinguishes fitness indicators from traits that contribute directly to survival and reproduction. Rather than performing a practical function, an indicator advertises the value of other adaptations. Peacock’s large tail illustrates this distinction: the energy spent growing it does not make the bird more efficient at an ordinary survival task; its significance lies in what the display communicates.

Cost and Credibility

The example turns on a conflict between collective efficiency and individual advantage. Peacocks as a species would be better off without the energy expenditure of large tails, but individual males have an incentive to grow the largest tail they can afford, while females have an incentive to choose the most impressive display they can attract. The resulting waste is not incidental to the signal. Under the Handicap principle, its cost helps make the signal credible: a display that demands substantial resources is harder to fake.

Role in the Argument

Peacock makes visible the book’s claim that courtship can transform waste into evidence. The tail’s extravagance, which looks counterproductive when measured by efficiency alone, gains value as a fitness indicator because its cost is legible. The example also prepares a comparison with human courtship, where a costly diamond ring can signal wealth in part because the giver must be able to afford it. In both cases, expenditure does more than represent capacity: the ability to bear the cost helps substantiate the claim.