User:Peter morrell/homology

In biology the general and quite ancient observation of similarity of form seen in the biological world of animals or plants. It is the name given to the anatomical correspondences between different species that biologists and paleontologists have noted and studied for centuries. This refers to similarities between related species.

Homology can be very easily confused with homoplasy. Homology refers to the similarity in form between closely related species, while by contrast, homoplasy refers to similarities of form that exist between unrelated species. Examples abound but include the claws of lizards, birds and bears, or the beaks of different birds which are not closely related in their structure in other ways.

Homoplasy suggests that the close similarity in structure has arisen not because the two groups are closely related, but because the structure in question possesses a form that fulfils a similar function in the lives of otherwise very different animals or plants. This suggests the possibility that substantially the same structure can arise and evolve in entirely separate phylogenetic groups through the evolutionary process of natural selection in which a form best-suited (most efficient) to the life of the organism is retained while less-suited forms that may have once existed are lost in the progress of time. Homoplasy is thus closely related to convergent evolution.