The function and evolution of child-directed communication

Abstract

Humans communicate with small children in unusual and highly conspicuous ways (child-directed communication (CDC)), which enhance social bonding and facilitate language acquisition. CDC-like inputs are also reported for some vocally learning animals, suggesting similar functions in facilitating communicative competence. However, adult great apes, our closest living relatives, rarely signal to their infants, implicating communication surrounding the infant as the main input for infant great apes and early humans. Given cross-cultural variation in the amount and structure of CDC, we suggest that child-surrounding communication (CSC) provides essential compensatory input when CDC is less prevalent-a paramount topic for future studies.

Fig 1. Evolutionary pathways of CDC.

A feature such as CDC with the function of aiding the acquisition of communicative competence can be (1) ancestral: homologously derived among African great apes and thus also found in humans; (2) unique among the great apes but convergently shared analogously with other, more distantly related species; or (3) newly evolved within our own species. Red represents the presence of IDC features. Outline credits: Human: T. Michael Keesey; Chimpanzee: Jonathan Lawley; Bonobo: T. Michael Keesey; Gorilla: T. Michael Keesey (after Colin M.L. Burnett); Orangutan: Gareth Monger; Gibbon: Kai R. Caspar; Tamarin: Yan Wong and T.F. Zimmerman; Zebra Finch: Jim Bendon (photography) and T. Michael Keesey (vectorization); Bat: Yan Wong; Squamate: Ghedo and T. Michael Keesey; Feline: Margot Michaud; Equine: T. Michael Keesey; Cetacean: Scott Hartman; Falcon: Liftarn; Fish, macaque and baboon are uncredited. Link to creative commons license: https://creativecommons.org/licenses/by-sa/3.0. Link to public domain license: https://creativecommons.org/publicdomain/zero/1.0. Outlines were downloaded from http://www.http://phylopic.org. The layout of the figure was achieved in R (version 4.1.2, R Development Core Team, 2012). CDC, child-directed communication; IDC, immature-directed communication.

Fig 2. Transition of CSC to CDC.

The transition of the importance of use of CSC to CDC. Darker color shows importance/presence and brighter color possible insignificance of CSC and CDC from early hominins to extant humans. CDC, child-directed communication; CSC, child-surrounding communication.