Evolution of neural circuits in the origin of behavioral novelty

The origin of phenotypic novelty is a central topic in evolutionary biology. In this review, I will discuss the neural circuit basis that underlies the emergence of behavioral novelties, emphasizing novel behaviors as evolutionary additions to existing behavioral repertoires and the circuit mechanisms crucial to their initial emergence, rather than their later refinement. I will describe two nonmutually exclusive mechanisms as possible common neural routes to behavioral novelty. First, existing motor modules can be redeployed for use in novel sensory-social contexts through transitions at circuit nodes linking decision-making and motor programs. Second, novel behavioral patterns can be encoded by the actualization of latent potentials in ancestral circuits. Together, these mechanisms suggest that nervous systems develop with remarkable potential to readily evolve new behaviors.