homology

homology , 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.

homology The basic similarity of a particular structure in different organisms: it usually results from their descent from a common ancestor.

homology The fundamental similarity of a particular structure in different organisms, which is assumed to be due to descent from a common ancestor. Two organs sharing a similar position, similar histological appearance, and a similar embryonic development are said to be homologous organs irrespective of their superficial appearance and function in the adult.