Human and chimp infants sometimes show facial movements while dozing that resemble smiles. Researchers show that this not only happens to higher-order primates like humans and chimpanzees, but also in newborn Japanese macaques, which are more distant relatives in the evolutionary tree.

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Human and chimp infants sometimes show facial movements while dozing that resemble smiles. Researchers show that this not only happens to higher-order primates like humans and chimpanzees, but also in newborn Japanese macaques, which are more distant relatives in the evolutionary tree.