The developmental genetics of homology.

Homology is an essential idea of biology, referring to the historical continuity of characters, but it is also conceptually highly elusive. The main difficulty is the apparently loose relationship between morphological characters and their genetic basis. Here I propose that it is the historical continuity of gene regulatory networks rather than the expression of individual homologous genes that underlies the homology of morphological characters. These networks, here referred to as 'character identity networks', enable the execution of a character-specific developmental programme.