Amotz Zahavi

(b.1928), Israeli biologist who has formulated a comprehensive theory of animal display and signaling. The theory asserts that the reliability, hence effectiveness, of signals depends on the cost, or handicap, born by the signaler. Zahavi is known for this so-called handicap principle, by which he intended to supplement and make more secure the Darwinian notion of sexual selection. A major problem with this notion or mechanism, which presupposes intraspecific rivalry for mates, is that it relies unduly upon anthropomorphic assumptions. In particular, especially within studies of the sub-branch of selection through female choice, many Darwinians have assumed that animals like the peacock have human standards of taste and beauty, as the peahen chooses the male with the more beautiful tail.

Rather than with human standards of beauty, Zahavi starts with the assumption that the males of a species must show the females that they are healthy and have the qualities needed in the female's offspring. Adornments as handicaps function as signs of excellence, but displays are always open to cheating by inadequate males who try to mimic the healthy and successful males. Hence, Zahavi suggests that such showing or displaying must involve features that are difficult for the inadequate to copy or falsify, such as large antlers, long tails, or other such physical characteristics.

Pushing this idea to the limit, Zahavi has suggested that such features that display health or strength might start to evolve in their own right until they are positively maladaptive, demonstrating to the females that their possessors can survive despite the handicaps. “Think of a woman watching two men run a race. If both arrive at the finishing post at the same time, but one has deliberately encumbered himself with a sack of coal on his back, the woman will naturally draw the conclusion that the man with the burden is really the faster runner” (Dawkins, 1978 p. 172).

Claims like this have been singled out by critics as paradigmatic examples of the just-so stories the Darwinians like to spin, with surface plausibility but little ground in reality. However, while it is certainly true that claims about the handicap principle pose problems in testing them, something not entirely dissimilar to the handicap principle is at the heart of William D. Hamilton's more compelling claims about the evolution of sex. Hence, even if not as first formulated, this principle, which applies to a wide range of signaling behavior (Zahavi and Zahavi, 1997), might survive in a modified form.