Early communicative gestures in human and chimpanzee 1-year-olds observed across diverse socioecological settings

Abstract

We investigated the communicative gestures used by chimpanzee and human infants. In contrast to previous studies, we compared the species at the same age (12–14 months) and used multiple groups living in diverse socioecological settings for both species. We recorded gestures produced by infants and those produce by others and directed toward infants. We classified the gestures into the following types: human-usual, chimpanzee-usual, and species-common; and searched for within species and between species differences. We found no significant differences between groups or species in overall rates of infant-produced or infant-received gestures, suggesting that all of these infants produced and received gestures at similar levels. We did find significant differences, however, when we considered the three types of gesture. Chimpanzee infants produced significantly higher rates of chimpanzee-usual gestures, and human infants produced significantly higher rates of human-usual gestures, but there was no significant species difference in the species-common gestures. Reports of species differences in gesturing in young infants, therefore, could be influenced by investigators’ choice of gesture type. Interestingly, we found that 1-year-old infants produced the gesture of “hold mutual gaze" and that the chimpanzee infants had a significantly higher rate than the human infants. We did not find strong evidence that the specific types of gestural environment experienced by young infants influenced the types of gestures that infants produce. We suggest that at this point in development (before human infants use lots of speech), nonverbal communicative gestures may be equally important for human and chimpanzee infants.

Forms and functions of gestures in preverbal 12- to 15-months old infants

“…Thereby, we also illustrate a phylogenetic continuity of flexibility underlying gestural communication in nonhuman and human primates. Similar methods used by Bard & Kishimoto (2023) have established the continuity of intentional communication between apes and 1-year old human infants. Ethological methods have also shown that gesture forms are shared between apes and human infants (Rodrigues et al, 2021;Kerksen et al, 2018), while whether these forms are retained in adult gestural communication is yet to be explored.…”