Paris - Babies match vocal sounds with the expression on their parents' faces, an essential phase in mastering speech, thanks to a genetic legacy shared by our primate relatives, biologists suggest.
Researchers in Germany say they have spotted a similar matching ability among rhesus monkeys.
They placed monkeys in front of two video monitors, each of which played a silent loop of another rhesus making facial expressions.
On one screen, the monkey made the distinctive expression for a long, friendly "coo" sound. One other, it made a different face, used to make a sharp, angry "threat" sound.
The scientists then placed loudspeakers which played either the "coo" or "threat" sound, and watched to see how the monkeys responded.
The monkeys swiftly linked the auditory cue with the visual one - they turned to the appropriate screen, looking at the right expression for the right sound.
They also looked longer when the match face was articulating the welcoming "coo" call rather than when it was making the aggressive "threat" call.
The findings, say the researchers, suggest that monkeys, like humans, have an inherent ability to match vocal patterns with facial expressions, and this seems to come from a common "evolutionary precursor".
Monkeys and apes shared a common ancestry with humans before primates diverged into humans and simians millions of years ago.
Among babies, matching skills are vital for learning how to communicate. By doing so, the infant associates speech with meaning.
The study, which appears in the British science journal Nature, is written by Asif Ghazanfar and Nikos Logothetis of the Max Planck Institute for Biological Cybernetics in Tuebingen. - Sapa-AFP