The Folly of Fools by Robert Trivers Read Free Book Online Page A

and mammals, this evolutionary struggle also favors intelligence on both sides. Consider the simple matter of picking out an object against a background. If the object has not been selected to match the background, it should be easy to detect, differing in numerous random details. But if there has been selection to match, detection is an entirely different matter. Selection will have obliterated many of the random mismatches, leaving a much more complex cognitive problem for the observer to solve.

THE COEVOLUTIONARY STRUGGLE BETWEEN DECEIVER AND DECEIVED
     
    The most important general principle is that deceiver and deceived are locked into a coevolutionary struggle. Since the interests of the two are almost always contrary—what one gains by perpetrating a falsehood, the other loses by believing it—a struggle (over evolutionary time) takes place in which genetic improvements on one side favor improvements on the other. One key is that these effects are “frequency dependent”—deception fares well when rare and poorly when frequent. And detection of deception fares well when deception is frequent but not when it is rare. This means that deceiver and deceived are locked into a cyclic relationship, in the sense that neither can drive the other extinct. Over time the relative frequencies of deceiver and deceived oscillate, but they do so within bounds that prevent either from disappearing. Likewise, in a verbal species like our own, we will be warned about new tricks more often by others the more frequent the tricks become. Note that no role is exclusive to some and not others—all of us are both deceiver and deceived, depending on context.

FREQUENCY-DEPENDENT SELECTION IN BUTTERFLIES
     
    You don’t have to look far to find evidence of frequency-dependent selection in systems of deception between prey and their predators. For example, in model/mimic systems, such as are found in butterflies (and snakes), a distasteful or poisonous species (model) evolves bright coloration to warn predators that it is distasteful. This selects for mimics, species that are perfectly tasty and harmless but gain protection by resembling the model. In West Africa, there is a genus of butterfly that is distasteful and as many as five species of the genus, all differing in coloration, may be found in the same forest. It turns out that there is a single species capable of mimicking all five model species. That is, females of the mimetic species can lay five kinds of eggs, each of which grows up to resemble one of the poisonous species.
    This unusual system of mimicry provides striking evidence of frequency-dependent selection. Here, one species is delicious but mimics any one of five related poisonous species. These differ in color and pattern, and so do their respective mimics. When several poisonous species are found in the same forest with their mimics, the frequency of each mimic within this species matches the frequency of the model among its group of related, distasteful species. This could have been brought about only by frequency-dependent selection, where each mimetic form loses value when it becomes too common relative to its own model. If all the tasty butterflies looked the same, the predatory birds would rapidly specialize on that one form, decimating it.
    One implication of frequency dependency is a perpetual premium on novelty. Indeed, in the above example, novel forms are more common in the mimetic species the more it outnumbers its model. That is, the more frequent the deceivers are, the more they begin to diversify, the better to avoid detection. Every new deception, by definition, starts rare and thereby gains an initial advantage. Only with success will one’s disguise become part of the backdrop against which another novelty can begin rare and flourish. We can also see how easily break-off forms in the mimic might happen to resemble a second poisonous species, leading to two forms mimicking two species.

AN EPIC