The evolution of vocal learning systems in birds and humans
Vocal learning is a rare trait found to date in only three groups of distantly related birds - parrots, hummingbirds, and songbirds - and four groups of distantly related mammals - humans, bats, cetaceans, and elephants. Remarkably, the three groups of birds have evolved seven similar forebrain vocal nuclei involved in vocal learning and production, and these are not found in their more closely related vocal nonlearning species. These vocal nuclei form two subpathways, and a posterior and an anterior vocal pathway. Humans have also evolved specialized brains areas for production of language. Here it is proposed that the anterior and posterior vocal pathways of vocal learning birds are similar to motor and premotor pathways for production and learning of language in humans. It is further proposed that these similarities arose because the vocal learning systems of birds and of humans may have evolved out of a pre-existing motor-premotor network used for other types of motor learning. © 2007 Elsevier Inc. All rights reserved.