The Role of Predators in Theories of Evolution

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Since evolution is an adaptive process, the predator-prey relationship is a major force in shaping the development of a species. An ineffective hunter will starve; prey that cannot evade the predator will be eaten. Those who survive to reproduce pass on their genes, and natural selection will favor such traits as speed, stealth, ability to camouflage, sensory acuity, or the ability to produce poison.

Predators and prey evolve together. If their relationship becomes unbalanced, it forces change. A predator without prey has to move where there is more prey, or change its diet. The absence of predators leads to overpopulation, which will result a population weakened by starvation and disease unless some of them migrate elsewhere.

The predator-prey relationship also occurs between plants and animals, fostering natural selection for change. The Galapagos tortoise likes to feed upon a certain type of cactus. On one island populated by long-necked tortoises, the branches of the cacti grow higher up than on a different island where the tortoises are short-necked. While there are other possible explanations, natural selection is a plausible reason for these differences. If the short-necked tortoises' necks get longer, we would expect the cactuses on that island to be changed as well.

Evolution in the predator-prey relationship changes not only physical characteristics, but social ones as well. Wolves and hyenas increase their efficiency by hunting in packs. Herd animals congregate and co-operate to avoid or repel predators, and warn each other of imminent danger.

Scientists theorize that the human tendency towards co-operation is the result of the necessity of working together to avoid predators. James Rilling at Emory University in Atlanta, has used brain imaging to show that co-operation is intrinsically rewarding for humans. Presumably, natural selection favored those individuals who enjoyed being part of team. According to Robert Sussman of Washington University, St. Louis, "Our intelligence, co-operation and many other features we have as modern humans developed from our attempts to out-smart the predator."

When the population of predators and prey oscillate together, they are tightly coupled ecologically. If the prey's population doesn't fluctuate while the predators' does, they are generally less tightly linked. However, scientists are investigating cryptic evolutionary dynamics which will keep a population stable by developing a new genotype which is less attractive to the predator. In this way, predation may favor biodiversity.

Without the predator-prey relationship, many species might be quite different in appearance and behavior. The law of the jungle seems cruel, but at the same time it keeps a population strong, healthy, and evolving.

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