自種・他種の乳児に対してチンパンジーとボノボは異なる見方を示す

抄録

In primates, infants are the special members in a society because they require extensive caretaking from adults. Intriguingly, in some species like chimpanzees, the appearance of an infant is clearly distinguished from that of an adult (e.g. white face) but in other species like bonobos, the appearance is relatively similar between infants and adults. In human previous studies, it is known that there is attentional bias for infants, while quite a few studies examined how adults perceive infants in non-human primates. This study examined viewing patterns for adult and infant individuals in chimpanzees and bonobos using a non-invasive eye-tracker. Fifteen chimpanzees and 6 bonobos participated in this study. We presented to them the pictures of mother-infant dyad of these species (both chimpanzees and bonobos) and an outgroup species (Japanese macaque). The total looking time for the adult and infant faces was analyzed. Chimpanzee participants showed significant infant looking bias to conspecifics. However, they showed marginally significant infant looking bias to the macaques, and neither adult nor infant looking bias to bonobos. The results suggest the existence of infant looking bias, which is supposed to help increasing provability of infant survival in chimpanzees. This bias is provably limited to own species. Conversely, bonobo participants showed significant adult looking bias to chimpanzees and macaques but not for bonobo. These results suggest that chimpanzees and bonobos have species-typical (but not species-general) interest to infants of own and other species.