Research paper in PLoS:

Macaque babies ape adults’ facial feats

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After an experimenter sticks his tongue out at a 3-day-old
macaque, the monkey returns the favour. (Ferrari, et al.)

“Scientists for the first time have established that for a brief period after birth, baby monkeys imitate facial movements made by people and adult monkeys. This copycat capacity, until now observed only in human and chimpanzee infants, seems to have evolved in all these primates as a way to jump-start newborns’ face-to-face communication with adults, say evolutionary biologist Pier F. Ferrari of the University of Parma in Italy and his colleagues.”

I tried this with my children when they were newly born… it was pretty cool watching them respond!