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Evolution: Frequently Asked Questions

No species exists in a vacuum; every form of life on Earth interacts over time with other organisms, as well as with its physical environment. For that reason, the evolution of one species influences the evolution of species with which it coexists by changing the natural selection pressures those species face. The classic examples of this sort of evolution, called coevolution, are predator-prey and host-parasite relationships.

One such predator-prey relationship exists between garter snakes and a species of salamander-like amphibian called a rough-skinned newt. In parts of the midwestern United States, garter snakes prey on newts, and probably have for thousands of years. In that time, over countless generations, the newts have evolved a powerful defense: a toxic chemical that they secrete through their skin. Where garter snakes are concerned, however, this defense mechanism has only been marginally successful. Generation after generation, as the newts became more poisonous, the snakes also evolved, developing greater tolerance to the newt's toxin. The result of this coevolutionary process, played out over countless snake and newt generations, is a chemical more toxic than almost any other natural substance on Earth, and a population of snakes that are seemingly immune to the toxin's effects.

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