... definition is also known as the biological species concept (BSC). Advocates of the BSC say that forms that are only slightly different (for example different geographical forms) may interbreed if they had the opportunity. Therefore they should be considered as the same species. However, supporters of the BSC also say that because two different forms seldom interbreed does not mean that they belong to the same species. A good example of this is wolves and coyotes, as they can mate and have fertile young. The phylogenetic species concept (PSC), however, states that different forms of the same kind of bird (for example) should be treated as separate species as these forms have evolved separately and have unique evolutionary histories. The PSC is becoming more popular definition, as it is less restrictive than the BSC. There is no worry about whether slightly different geographic forms may interbreed, and no need to ...

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