Evolution of Birdsong Learning and Human Spoken Language
Vocal learning is one of the most critical components of spoken language. It has only evolved several independent times among mammals and birds. Although all vocal learning species are distantly related and have closer relatives that are non-vocal learners, humans and the vocal learning birds have evolved convergent forebrain pathways that control song and speech imitation and production. Here I will present an overview of the various biological hypothesis of what makes vocal learning and spoken language special, how it evolved, and what differs about the molecular and neural mechanisms compared to other behavioral traits. We find convergent changes in gene regulation in song learning brain pathways in birds and spoken language brain pathways in humans. These genes are enriched for functions in brain connectivity, neural activity, and synaptic plasticity. The specialized regulation is associated with convergent accelerated regulatory regions. To explain these findings, I propose a motor theory of vocal learning origin, in which brain pathways for vocal learning evolved by brain pathway duplication of an ancestral motor learning pathway. The duplicated pathway uses mostly the same genes, but with divergences in gene regulation via sequence and epigenetic changes, which control divergent connectivity and other specialized functions to rapidly integrate auditory input with vocal motor output.