| When a geographic barrier, such as the Grand Canyon, prevents members of a population from interbreeding, the groups evolve independently of one another and may eventually constitute two or more species. For example, although they descended from the same original population, the squirrels on the south rim of the Grand Canyon now belong to an entirely different species than the squirrels on the north rim. By comparison, birds and other animals capable of crossing the divide continue to interbreed and so remain members of the same species. |
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