Sonya Kahlenberg from Bates College and Richard Wrangham from Harvard University have been studying wild chimpanzees in Uganda for the past 14 years. During that time, they’ve discovered numerous examples of young chimps treating sticks like dolls.
In all, the researchers counted over a hundred examples of chimps carrying around sticks, taking them into their nests at night, playing with the sticks, and even making separate nests for those sticks. Most of this play was done by juvenile females, and was rarely practiced by males or adults. Also, the stick-carrying behavior ended as soon as the females had babies of their own. Taken together, the data certainly seems to suggest that the females were using the sticks as practice babies. In other words, as dolls.This is interesting for two reasons. First, this behavior seems to indicate the kind of complex representational view of objects that was thought to be the purview of humans alone. Second, because the use of the sticks as dolls was present mainly in females, this indicates that sexual preference for types of toys may predate human evolution.