Homology in psychology, as in biology, refers to a relationship between characteristics that reflects the characteristics' origins in either evolution or development. Homologous behaviors can theoretically be of at least two different varieties. As with homologous anatomical characteristics, behaviors present in different species can be considered homologous if they are likely present in those species because the behaviors were present in a common ancestor of the two species. Alternatively, in much the same way as reproductive structures are considered homologous because they share a common origin in embryonic tissues, behaviors—or the neural substrates associated with those behaviors—can also be considered homologous if they share common origins in development.