A character shared by a set of species and present in their common ancestor. Compare with analogy. (Some molecular biologists, when comparing two sequences, call the corresponding sites "homologous" if they have the same nucleotide, regardless of whether the similarity is evolutionarily shared from a common ancestor or convergent. They likewise talk about percent homology between the two sequences. Homology in this context simply means similarity. This usage is frowned upon by many evolutionary biologists, but is established in much of the molecular literature. )