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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.