Although analogous characteristics are superficially similar, they are not homologous because they are phylogenetically independent. In the above example, the bird and bat wings are analogous as wings, but homologous as forelimbs because the organ served as a forearm (not a wing) in the last common ancestor of tetrapods.Īnalogy is different than homology. It is important to distinguish between different hierarchical levels of homology in order to make informative biological comparisons. Wings evolved independently in each lineage after diverging from ancestors with forelimbs that were not used as wings (terrestrial mammals and theropod dinosaurs, respectively).

Genetically, a bat wing and a bird wing have very little in common the last common ancestor of bats and birds did not have wings like either bats or birds. Bat wings and bird wings evolved independently and are considered analogous structures. The opposite of homologous structures are analogous structures, which are physically similar structures between two taxa that evolved separately (rather than being present in the last common ancestor). This is a common problem in bioinformatics when genomes of different species have been sequenced and homologous genes have been found, one can not immediately conclude that these genes have the same or similar function, as they could be paralogs whose function has diverged. For example, the hemoglobin gene of humans and the myoglobin gene of chimpanzees are considered paralogs. Paralogous genes often belong to the same species, but not always. This is because they are similar characteristically and even functionally, but evolved from different ancestral roots. analogy: The wings of pterosaurs (1), bats (2), and birds (3) are analogous as wings, but homologous as forelimbs.

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