According to a 14 year old study in Uganda, young chimps play make believe games

December 21, 2010- Source: The Globe & Mail

According to a 14 year old study in Uganda, young chimps play make believe games in which they pretend their favorite stick is a baby for nurturing and even putting to bed. The study provides evidence that differences in the way girls and boys act are a genetically hard-wired element. Both sexes collected sticks as toys but females treated them like dolls- carrying them from tree to tree, patting & cuddling them, and involving them in simple games. The male on the other hand made a nest for the stick next to his own and put the stick to bed. The males stopped playing with the stick once they reached adulthood while the females only stopped until they had a baby of their own. Two-thirds of the chimps who had sticks were female. This reflects that biological factors, and not just social are in play.