Guest post by graduate student Kia Walcott

In a culture that seems to value outgoing personalities, the quiet kid in the corner may have the upper hand.

Since our lineage moved away from other primates, the human personality has evolved in a way that affects a broad range of behaviors. A study conducted by Duke anthropologist Brian Hare and psychologist Esther Herrmann at the Max Planck Institute of Evolutionary Anthropology compared the reaction of our closest ape relatives, the chimpanzee and the bonobo, to the reaction of human infants age 2.5 years to unfamiliar objects and people. (Orangutans were also included in this study as an ‘outgroup’.)

The baby family tree of primates

The ape family tree, decorated with adorable babies. (image adapted from

Test subjects were presented with items from three categories: human, object, and food.  The items within each category varied in familiarity (human: stranger vs. non-stranger), newness and excitement (objects: boring, bland toy vs. loud, exciting toy) and preference (food: delicious vs. not so delicious).  The items were presented differently over a period of three days. On day one, the items were only visible, on the second day the items were moved, and on day three the items could be touched.  The attraction to or avoidance of the unfamiliar objects was used to measure the test subject’s shyness or boldness.

Human children avoided unfamiliarity and thus most closely resembled the behavior of bonobos, though these apes did not seem to show either avoidance or attraction to the unfamiliar items. Chimpanzees and orangutans approached unfamiliar food and objects more quickly.

The differences seen across species may help explain the development of how we as humans think and react in social situations. For example, a shyer child may be more likely to seek reassurance from parents and peers, which in turn provides an opportunity for social learning and teaching that is unique to humans.

The results of this study also suggest that differences in ecology or where we live shape responses to uncertainty and risk-taking behaviors. Chimpanzees and orangutans have evolved in more unpredictable feeding environments than humans or bonobos, and Hare believes  this may explain why, despite being distantly related, these two species showed a similar attraction to unfamiliarity. Chimpanzees and orangutans may have evolved preferences that favor risk over certainty, especially when food payoffs are involved.

On the other hand, Bonobos evolved in an environment with plentiful resources where competition within the group and male aggression are less common.

Research done on domesticated animals has shown that in an environment where male aggression is less common, there is a decrease in both exploratory behavior and stress in new situations. This may explain why bonobos did not seem to care as much about the items presented.

It seems that a more reserved personality may predict better social interaction and thinking later in life.

Citation:  “A comparison of temperament in nonhuman apes and human infants,” Herrmann et al. Developmental Science, Nov. 2011. DOI: 10.1111/j.1467-7687.2011.01082.x