A comparison of temperament in nonhuman apes and human infants.

The adaptive behavior of primates, including humans, is often mediated by temperament. Human behavior likely differs from that of other primates in part due to temperament. In the current study we compared the reaction of bonobos, chimpanzees, orangutans, and 2.5-year-old human infants to novel objects and people - as a measure of their shyness-boldness, a key temperamental trait. Human children at the age of 2.5 years avoided novelty of all kinds far more than the other ape species. This response was most similar to that seen in bonobos and least like that of chimpanzees and orangutans. This comparison represents a first step in characterizing the temperamental profiles of species in the hominoid clade, and these findings are consistent with the hypothesis that human temperament has evolved since our lineage diverged from the other apes in ways that likely have broad effects on behavior. These findings also provide new insights into how species differences in ecology may shape differences in temperament.