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In evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes, traits, or species, that develop adaptations and counter-adaptations against each other, resembling an arms race, which could be, and often are, described as examples of positive feedback.〔Dawkins, R. 1996. ''The Blind Watchmaker'' New York: W. W. Norton. Note: This book was also published by Penguin in 1991. While the text is identical, page numbers differ〕 The co-evolving gene sets may be in different species, as in an evolutionary arms race between a predator species and its prey (Vermeij, 1987), or a parasite and its host. Alternatively, the arms race may be between members of the same species, as in the manipulation/sales resistance model of communication (Dawkins & Krebs, 1979) or as in runaway evolution or Red Queen effects. One example of an evolutionary arms race is in sexual conflict between the sexes, often described with the term Fisherian runaway. Thierry Lodé〔Thierry Lodé "La guerre des sexes chez les animaux" Eds Odile Jacob, Paris ISBN 2-7381-1901-8;〕 emphasized the role of such antagonist interactions in evolution leading to character displacements and antagonist coevolution. The escalation hypothesis put forward by Geerat Vermeij speaks of more general conflicts and was originally based on his work with marine gastropod fossils. Co-evolution itself is not necessarily an arms race. For example, mutualism may drive co-operative adaptations in a pair of species. This is the case with certain flowers' ultra-violet color patterns, whose function is to guide bees to the center of the flower and promote pollination. Co-evolution is also interspecific by definition; it excludes intraspecific arms races such as sexual conflict. Evolutionary arms races can even be displayed between humans and micro-organisms, where medical researchers make antibiotics, and micro-organisms evolve into new strains that are more resistant. Evolutionary arms races often evolve when a trait is only beneficial compared to the population. For instance, if a tree has a mutation making it taller, it will have an advantage due to more sunlight. But as soon as other trees reach the same height, it loses that advantage. As soon as a taller tree appears, it has the advantage. In this example, the nearest peak of the evolutionary landscape moves as the population approaches it. Another example of runaway evolution in sexual selection is an elk's antlers. Having big antlers makes a male elk more likely to win a mate. In fact, having big antlers is a requirement to mate. As a result, elk evolve antlers that are incredibly costly to build, maintain, and fight with. By the end of the mating season, the average male loses 25% of his body weight due to fighting, which he has to make up before winter starts. == Symmetrical versus asymmetrical arms races == Arms races may be classified as either symmetrical or asymmetrical. In a symmetrical arms race, selection pressure acts on participants in the same direction. An example of this is trees growing taller as a result of competition for light, where the selective advantage for either species is increased height. An asymmetrical arms race involves contrasting selection pressures, such as the case of cheetahs and gazelles, where cheetahs evolve to be better at hunting and killing while gazelles evolve not to hunt and kill, but rather to evade capture. This asymmetric example could be more generally seen as the life-dinner principle. The life-dinner principle is the idea that in a situation with the predator and prey, the prey gets the short end of the stick with either injury or death while the predator just has the inconvenience of having to find another meal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「evolutionary arms race」の詳細全文を読む スポンサード リンク
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