What is the X in X-mas?
in biology, similarity of function and superficial resemblance of structures that have different origins. For example, the wings of a fly, a moth, and a bird are analogous because they developed independently as adaptations to a common function-flying. The presence of the analogous structure, in this case the wing, does not reflect evolutionary closeness among the organisms that possess it. Analogy is one aspect of evolutionary biology and is distinct from homology (q.v.), the similarity of structures as a result of similar embryonic origin and development, considered strong evidence of common descent