Vestigiality

The concept of vestigiality applies to genetically determined structures or attributes that have apparently lost most or all of its ancestral function in a given species. Assessment of the vestigial status must generally rely on comparison with homologous features in related species. The emergence of vestigiality occurs by normal evolutionary processes, typically by loss of function of a feature that is no longer subject to positive selection pressures when it loses its value in a changing environment. More urgently the feature may be selected against when its function becomes definitely harmful. Typical examples of both types occur in the loss of flying capability in island-dwelling species.