Down-to-earth genetics

The genetics of behavioural differences between closely related species are less well understood than the genetics of morphological differences. Many animals build elaborate structures — such as hives, nests and burrows — that 'evolve' as natural selection acts on the behaviour of their builders. This study uses an example of this phenomenon to tackle the question of whether complex behaviours evolve through one or few genetic changes that each influence many aspects of behaviour, or by accumulation of several genetic changes that generate behavioural complexity only when combined. Hopi Hoekstra and colleagues show that the complex burrows created by oldfield mice are governed by several genetic modules, each controlling an aspect of burrow size or shape. This modularity in burrow architecture suggests that complex behaviour may result from the combination of genetically determined behaviours that have accumulated over time.