Homology (biology)
![The principle of homology: The biological derivation relationship (shown by colors) of the various bones in the forelimbs of four vertebrates is known as homology and was one of Charles Darwin’s arguments in favor of evolution.](/Images/godic/202501/18/Homology_vertebrates-en.svg0802.png")
![The wings of pterosaurs (1), bats (2) and birds (3) are analogous as wings, but homologous as forelimbs.](/Images/godic/202501/18/Homology0802.jpg")
![A sequence alignment, produced by ClustalO, of mammalian histone proteins.
Sequences are the amino acids for residues 120-180 of the proteins. Residues that are conserved across all sequences are highlighted in grey. Below the protein sequences is a key denoting conserved sequence (*), conservative mutations (:), semi-conservative mutations (.), and non-conservative mutations (&nsbp;).[13]](/Images/godic/202501/18/Histone_Alignment0802.png")
![](/Images/godic/202501/18/Crossopterygii_fins_tetrapod_legs0803.JPG")
In the context of biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates. Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.