"Unwilling" versus "unable": Understanding chimpanzees' restrictions in cognition and motivation.

Human uniqueness and its evolutionary basis are explored through a comparison between humans and our closest evolutionary animals. With this approach, any behavior not demonstrated by non-human animals is considered unique to humans. We often attribute human uniqueness to a highly sophisticated cognitive ability that seemingly exists only in humans. However, even though non-human animals do not demonstrate a certain behavior, it is too early to say that they cannot demonstrate it. In this article, I introduce some examples in which chimpanzees have a cognitive basis for some social or cultural behaviors but do not perform these in their everyday lives, which urges us to consider not only cognitive restrictions but also motivational restrictions. I propose four hypotheses to explain their inaction. This type of “growth allowance" of cognitive abilities may help animals survive when they are challenged under a novel selective pressure during the exploration of a new environment.