Cooperative care and the evolution of the prelinguistic vocal learning.

The development of the earliest vocalizations of human infants is influenced by social feedback from caregivers. As these vocalizations change, they increasingly elicit such feedback. This pattern of development is in stark contrast to that of our close phylogenetic relatives, Old World monkeys and apes, who produce mature-sounding vocalizations at birth. We put forth a scenario to account for this difference: Humans have a cooperative breeding strategy, which pressures infants to compete for the attention from caregivers. Humans use this strategy because large brained human infants are energetically costly and born altricial. An altricial brain accommodates vocal learning. To test this hypothetical scenario, we present findings from New World marmoset monkeys indicating that, through convergent evolution, this species adopted a largely identical developmental system-one that includes vocal learning and cooperative breeding.