Experts have long suspected that complex social interaction drove the evolution of large brains in humans. Now a study in wasps supports and refines that theory: it seems that dominant individuals have larger brain regions responsible for higher-order cognitive processes.

Biologists at the University of Washington observed the behavior of paper wasps (Mischocyttarus mastigorphorus) in the Costa Rican rain forest and then measured the size of their brains. The researchers found that the so-called mushroom bodies, the lobes that underlie learning and memory in insects, were larger in dominant wasps than in their subordinate peers.

Mushroom bodies are the insect equivalent of the human neocortex, the outer layer of our brain, which handles complex cognition. Scientists have already established that the neocortex and the mushroom bodies are larger in social species such as humans and wasps, as compared with solitary animals such as bears and lone spiders. The new study suggests that competition for rank may have been a key factor in the evolution of this intelligence.

This story was originally printed with the title, "Big Brains Dominate".