homology hōmŏl´əjē [key], in biology, the correspondence between structures of different species that is attributable to their evolutionary descent from a common ancestor. For example, the forelimbs of vertebrates, such as the wing of bird or bat, and the foreleg of an amphibian, are homologous there is an almost identical number of bones in the limbs, and the pattern construction is identical. Homologous structures do not necessarily have to have the same function the wings of birds and forelegs of a horse are homologous through they clearly serve different functions. Analogy is the functional similarity between structures that do not have a common origin for example, the wings of birds and those of insects are analogous.

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