In 1970, British ethologists P. M. Driver and D. A. Humphries suggested that these rat and moth behaviors were examples of "protean behavior." They named this kind of adaptive unpredictable behavior after the mythical Greek river-god Proteus. Many enemies tried to capture Proteus, but he eluded capture by continually, unpredictably changing from one form into another— animal to plant to cloud to tree. Driver and Humphries's 1988 book Protean Behaviour: The Biology of Unpredictability presented a detailed theory of randomized behavior, supported by a wide range of field observations. Unfortunately they did not make the connection to mixed strategies in game theory, so these prophets of genetic indeterminism did not have the influence they deserved in evolutionary theory.
The logic of proteanism is simple. If a rabbit fleeing from a fox always chose the single apparently shortest escape route, the consistency of its behavior would make its escape route more predictable to the fox, its body more likely to be eaten, and its genes less likely to replicate. Predictability is punished by hostile animals capable of prediction. Instead of fleeing in a straight line, rabbits tend to zigzag erratically—a protean escape behavior that makes rabbits much harder to catch. Like the moth, the rabbit probably evolved special brain mechanisms to randomize its escape path.
Protean escape is probably the most widespread and successful adaptation against being eaten by predators, and is used by virtually all mobile animals on land, under water, and in the air. Proteanism explains why it is harder to predict the movements of a common housefly for the next ten seconds than the orbit of Saturn for the next ten million years. Yet there is more to proteanism than escape behavior. The effectiveness of almost any behavior can be enhanced by making its details unpredictable to evolutionary opponents. For example, predators also use proteanism to confuse prey. When a weasel is stalking a vole, it may do a "crazy dance." The weasel jumps about like a mad thing, chases its tail, shakes its head, licks its feet, all the while positioning itself closer and closer to its bemused prey. The seemingly pointless series of weird actions baffles the vole. The vole is caught in a web of confusion. Australian aborigine hunters did similar wild dances to mesmerize the kangaroos they hunted. Perhaps our hominid ancestors did too.
Animal play behavior also reveals the importance of proteanism. Most animal play is play-chasing and play-fighting. At the level of movement patterns, play is a way of practicing pursuit and evasion. But at the psychological level, it is a way of practicing prediction and proteanism.
Unpredictability can be useful at many levels. When threatened, octopuses and cuttlefish use "color convulsions."
Their pigmented skin cells, which are under direct control of the nervous system, display an unpredictable series of color patterns to confound the perceptual expectations of predators. One moment the cuttlefish has black stripes, the next it has red spots, which makes it hard for predators to keep in mind what they're supposed to be chasing. The lesson of proteanism is very general: whenever one animal benefits from being able to predict something about another animal's behavior or appearance, the second animal might benefit from making its behavior or appearance unpredictable.
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