∞ generated and posted on 2016.11.05 ∞
Aspect of two organisms, typically two different species, that is similar because the common ancestor to both organisms also possessed that feature.
Homologous characters typically display similar patterns of embryonic development or otherwise show similarity on fine as well as coarse scales (e.g., macroscopically as well as molecularly).
Homologies in DNA or polypeptide sequences are readily detected in the course of DNA sequencing and their detection has been a spectacular byproduct of the extensive DNA sequencing that has followed the sequencing of the human genome.
See also homologous structure, vestigial structure, and identical by descent.
Homologies contrast with what can be described as analogies, homoplasies, and simply unrelated characteristics. The first two, analogies and homoplasies, are products of what is known as convergent evolution—where two characters are similar because they do similar things in similar ways. That is, analogies tend to be similar solutions solving similar problems, but otherwise did not evolve identically from the same characteristic in two different organism lineages.
The forelimbs of all tetrapods are homologous structures, indeed ones that are shared with fish, but the wings of birds are only analogous with the wings of bats since while their common ancestor, a kind of reptile, possessed the tetrapod forelimb, that reptilian ancestor did not possess wings.