Dec 21, 2010 13:19 GMT  ·  By

It appears that little girls are not the only ones that play with dolls, since scientists at Harvard University and Bates College noticed that young female chimpanzees treat sticks like they were dolls and carry them around until they have offspring of their own.

Another interesting thing is that this kind of behavior is far less frequent in young males.

The general belief is that children are influenced by others in their choice of toys and this is why girls play with dolls and boys play with cars.

But this new study carried out by Sonya M. Kahlenberg and Richard W. Wrangham, gives the first evidence of a wild non-human species playing with primitive dolls, and also the first known sex difference in an animal's choice of playthings.

So the researchers say that maybe children are not simply conditioned by others as to what they play with, but rather they are probably born with their own ideas of the way they want to behave.

They analyzed data on chimpanzee behavior, gathered over a period of 14 years by the Kibale National Park in Uganda, and identified over 100 cases of stick-carrying.

Most of the times, the young females did not use the sticks for fighting or foraging like adults do sometimes, instead they carried them into the nest to sleep with them, and one time, a female even built another nest for the stick.

The two researchers even saw the animals playing the 'airplane game' – lying on their back and balancing their offspring across their upraised hands.

Wrangham, who is also the Ruth Moore Professor of Biological Anthropology at Harvard, said that they “have seen juveniles occasionally carrying sticks for many years, and because they sometimes treated them rather like dolls, we wanted to know if in general this behavior tended to represent something like playing with dolls.

“If the doll hypothesis was right we thought that females should carry sticks more than males do, and that the chimpanzees should stop carrying sticks when they had their first offspring.

“We have now watched enough young chimpanzees to test both points.”

The researchers also observed a few adult females carrying sticks, but that behavior stopped once they became mothers for the first time.

They believe that doll play among humans could have originated in object-carrying by earlier apes, which means that toy selection does not depend entirely on socialization.

Kahlenberg, who is also a lecturer in biology at Bates and conducted the research as a postdoctoral researcher in Wrangham's group at Harvard, says that “in humans, there are robust sex differences in children's toy play, and these are remarkably similar across cultures.

“While socialization by elders and peers has been the primary explanation, our work suggests that biology may also have an important role to play in activity preferences.”

Wrangham added that “obviously in humans there is a huge role for peers, parents, and others to influence a child's preferences for different kinds of toys, and the same may well be true of chimpanzees.

“One of the things that makes our finding fascinating is that there is little evidence of anything comparable in other chimpanzee communities, which raises the possibility that the chimpanzees are copying a local behavioral tradition.

“So this may be a lovely case of biological and social influences being intertwined.”

This new study was described this week in the journal Current Biology.