The term "convergence" is used to describe the presence of a similar feature in two or more taxa that are not closely related. Convergent features evolve independently often as a result of natural selection operating on unrelated taxa that occupy similar environments. The recognition of convergence requires an accurate phylogeny. With a phylogenetic hypothesis, homologous characters can be distinguished from analogous traits. Convergent structures are usually derived from different morphological features or by different developmental pathways (although this is not the case in one special class of convergence described below).

Convergence can be further broken down into specific phenomena. Analogy describes the convergent modifications of a nonhomologous trait. For example, analogous organs may share a common function but develop from different tissue types in unrelated organisms. The wings of insects and the wings of birds have the same functional role (flight) but they are derived from nonhomologous structures...