Young chimps play make-believe games in which they pretend that a favorite stick is a baby for nurturing and even putting to bed, according to a 14-year study of the animals in Uganda.
Biologists watched the chimps in the forests of Kibale National Park in Uganda and found intriguing differences in the way young males and females passed their time — providing evidence that differences in the way boys and girls play may have a genetically hardwired element.
While both sexes collected sticks to use as toys, females often treated them like dolls, carrying their sticks from tree to tree, patting and cuddling them, and involving them in simple games. In one case, a young male chimp made a small nest next to his own and appeared to put his stick to bed.
The few males in the group that played with stick dolls stopped when they reached adulthood. However, females carried on the parental role-playing game and only stopped when they gave birth to their first baby. Two-thirds of the chimps that kept stick dolls were female.
The findings suggest that -biological factors — rather than social influences alone — play some role in shaping toy preferences in childhood.
“There are predispositions, biological influences, that lead females and males to treat sticks differently,” said Richard Wrangham, an evolutionary biologist at Harvard University. “What we’ve got here is evidence that without any kind of socialization by adults, females seem to be predisposed to react to sticks as though they were dolls.”
This could reflect more female interest in infant care and playing at mothering.
The use of stick dolls appears to be a first for wild chimpanzees and may be a social tradition that has sprung up as a one-off in the Kanyawara chimpanzee community in Kibale, Wrangham said.
The claim that boys and girls are biologically prone to favor one kind of toy over another is controversial. Other explanations point to peer behavior and sexual stereotyping by parents as more important influences.
The research, co-authored by Sonya Kahlenberg at Bates College in Maine, appears in the journal Current Biology.