The evolution of infant-directed communication: comparing vocal input across all great apes

Human language is unique among communication systems since many elements are learned and transmitted across generations. Previous research suggests that this process is best predicted by infant-directed communication, i.e., a mode of communication directed by caregivers to children. Despite its importance for language, whether infant-directed communication is unique to humans or rooted more deeply in the primate lineage remains unclear. To assess this, we investigated directed and surrounding vocal communication in human infants and infants of wild nonhuman great apes. Our findings reveal that human infants receive dramatically more infant-directed communication than nonhuman great ape infants. These data suggest that the earliest hominins likely relied more on surrounding communication to become communicatively competent, while infant-directed vocal communication became considerably more prominent with human language. Human infants receive more directed communication than other great ape infants, indicating that it evolved alongside language.