In order to formulate hypotheses about the evolutionary underpinnings that preceded the first glimmerings of language, mother-infant gestural and vocal interactions are compared in chimpanzees and humans and used to model those of early hominins. These data, along with paleoanthropological evidence, suggest that prelinguistic vocal substrates for protolanguage that had prosodic features similar to contemporary motherese evolved as the trend for enlarging brains in late australopithecines/early Homo progressively increased the difficulty of parturition, thus causing a selective shift toward females that (...) gave birth to relatively undeveloped neonates. It is hypothesized that hominin mothers adopted new foraging strategies that entailed maternal silencing, reassuring, and controlling of the behaviors of physically removed infants (i.e., that shared human babies' inability to cling to their mothers' bodies). As mothers increasingly used prosodic and gestural markings to encourage juveniles to behave and to follow, the meanings of certain utterances (words) became conventionalized. This hypothesis is based on the premises that hominin mothers that attended vigilantly to infants were strongly selected for, and that such mothers had genetically based potentials for consciously modifying vocalizations and gestures to control infants, both of which receive support from the literature. Key Words: bipedalism; brain size; chimpanzees; foraging; gestures; hominins; infant riding; motherese; prosody; protolanguage. (shrink)
My responses to the observations and criticisms of 26 commentaries focus on the coregulated and affective nature of initial mother/infant interactions, the relationship between motherese and emergent linguistic skills and its implication for hominin evolution, the plausibility of the “putting the baby down” hypothesis, and details about specific neurological substrates that may have formed the basis for the evolution of prelinguistic behaviors and, eventually, protolanguage.
Unlike chimpanzees, human infants engage in persistent adult-directed (AD) crying, and human mothers produce a special form of infant-directed vocalization, known as motherese. These complementary behaviors are hypothesized to have evolved initially in our hominin ancestors in conjunction with the evolution of bipedalism, and to represent prelinguistic substrates that paved the way for the eventual emergence of protolanguage.