Neonatal imitation in rhesus macaques.
Level 5 - mechanism / opinion, no new human data
Animal experimental study without human data (CEBM Level 5).
PubMed 16953662 · doi:10.1371/journal.pbio.0040302
What was done
Researchers tested behavioral responses in newborn rhesus macaques (Macaca mulatta) exposed to human facial and hand gestures, including lip smacking, tongue protrusion, mouth opening, hand opening, and eye opening/closing (control condition), across early postnatal days.
What was found
The abstract does not report exact numerical values or sample sizes. It reports that by day 3 of life, infant macaques imitated lip smacking and tongue protrusion. On day 1 of life, human mouth opening elicited matched lip smacking behavior in the infants. These imitative behaviors occurred at an early developmental stage and appeared confined to a narrow temporal window.
Why it matters
This study demonstrates that neonatal imitation of communicative facial gestures is not exclusive to humans or apes, suggesting an older evolutionary origin tied to primate affiliative interactions.
Limits
The study was conducted in a non-human primate model using human demonstrators rather than conspecifics. The abstract does not provide the sample size (n), exact gesture frequencies, or statistical effect sizes, and it does not define the precise duration of the developmental window beyond the earliest days of life.
Cited by
- supports Lip-smacking is an affiliative social behavior in monkeys.