Figure 1.

Evolution of ‘homologous’ behaviours. The evolution of similar behaviours across taxa, such as sex or aggression, represents a key developmental and evolutionary phenomenon for understanding genetic and developmental paths through which specific behaviours can be realized. Here, the question is whether similar behaviours can have a different neuronal basis (1), whether particular behaviours can only rest upon conserved neuronal (2) and genetic mechanisms (3) or whether—as in the construction of functionally similar morphological structures [62]—similar behaviours can have the same genetic but different neuronal (i.e. developmental) basis (4).