That's according to a new study from Kyoto University's Primate Research Institute, where researchers observed several dozen smiles from seven macaque newborns.
Spontaneous smiles in infants – facial movements that frequently happen during sleep and have no discernible cause, internally or externally – have, of course, been seen in humans and also, more recently, in chimpanzees.
"About a decade ago we found that chimp infants also display spontaneous smiles," said study co-author Masaki Tomonaga in a statement. "Since we see the same behavior in more distant relatives, we can infer that the origin of smiles goes back at least 30 million years, when old world monkeys and our direct ancestors diverged."
As can be seen in the video, the word "smiling" is used broadly, when compared with the everyday impression of what constitutes, say, a human smile.
"Spontaneous macaque smiles are more like short, lop-sided spasms compared to those of human infants," explained Kawakami.
Read more at Discovery News