Jumping to Bold Conclusions a Review of the Handicap Principle: a Missing Piece of Darwin's Puzzle Group Therapy

Occasionally, a grazing gazelle notices the approach of a predatory lion. Rather than immediately taking ight at top speed, she often jumps high in the air several times before eeing. Perhaps these \stots" are warnings to close-by, possibly related, gazelles? If this is the case why is the warning so energetic? Surely evolution would favor less exhausting signals, since exhaustion is to be avoided when one is about to be pursued by a predator? Amotz and Avishag Zahavi open their recent book with a diierent explanation for this behavior. They maintain that the stotting gazelle is not warning conspeciics of danger but informing the lion of its own escape ability. Because the lion has no desire to waste time and energy fruitlessly chasing uncatchable prey, this information is of use to it, but only if the information is truthful. It is here, the Zahavis claim, that an explanation is to be found for the otherwise inexplicable brio of the gazelle's display. The authors construe the stotting display as a handicap | a signaling behavior that incurs the depletion of the very quality it advertises. They interpret the gazelle's vigorous leaping to convey the honest message that she is t enough and fast enough to waste just so much of her time and energy on jumping. The \handicap principle," which underwrites the account of stotting ooered above, has been the subject of energetic debate within the evolutionary biology literature since Israeli ornithologist Amotz Zahavi rst presented it over 20 years ago (Zahavi, 1975, 1977). Despite initially attracting considerable skepticism, and enjoying only intermittent empirical and theoretical support over the next decade and a half, it has achieved increasing notoriety. More recently, the central tenets of the theory have earned acceptance as a result of the publication of a number of successful game-theoretic models (Grafen, 1990, being foremost among these). While the handicap principle has yet to gain the status of canonical edict (Zahavi having thus far, for instance, failed to garner much support for his contention that it eclipses \most" of Darwin's theory of sexual selection), both the vocabulary and explanatory perspective associated with it have attained a central position within current evolutionary thinking. In addition to critiquing the Zahavis' new book, this review will give a avor of the perspective aaorded by the handicap principle and in doing so will highlight an area of biological thinking that might proot from …