Japanese macaque infants smile in their sleep

When human and chimp infants are dozing, they sometimes show facial movements that resemble smiles. These facial expressions -- called spontaneous smiles -- are considered the evolutionary origin of real smiles and laughter. Researchers at Kyoto University's Primate Research Institute 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. 川上文人 霊長類研究所研究員、友永雅己 同教授、鈴木樹理 同准教授らのグループ