When Jane Goodall first reported that chimps use tools, our concept of human uniqueness was rocked. It has never quite recovered. In another twist, a population of wild chimps of the Kanyawara community in Uganda鈥檚 Kibale National Park appears to be using objects as toys.
That鈥檚 remarkable in itself, but of Bates College in Lewiston, Maine, and of Harvard University, found that juvenile chimps in this population play with sticks like children play with dolls, cradling them and even making nests for them to sleep in at night 鈥� and they found that the behaviour is more common in females.
鈥淚 favour the hypothesis that stick carrying is practice for the adult role of motherhood,鈥� says Kahlenberg, 鈥減erhaps similar to functions of other kinds of play, being practice for adult roles.鈥�
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Before birth
Kahlenberg and Wrangham analysed data from 14 years of observation of wild chimps and categorised stick-use into four classes: as probes to investigate holes; as weapons during aggressive displays or attacks; as a prop during solitary play, and, in essence, as dolls. This last class they call 鈥渟tick carrying鈥�, and in 301 observations it turned out to be more common in juvenile chimps, more frequent in females than males, and only occurred in females before their first birth (Current Biology, DOI: 10.1016/j.cub.2010.11.024).
鈥淚t was striking that this behaviour was seen in some adult females, but never after they became mothers,鈥� says Kahlenberg, adding that the chimps learned the behaviour by copying other juveniles, not adults.
On at least 25 occasions the stick-dolls were carried by the young chimps into day nests 鈥� a behaviour not observed when sticks were used for other purposes. One young male made a separate nest for his doll, and a female was seen patting a log like she was 鈥渟lapping the back of an infant鈥�, which occurred while her mother was caring for a sick sibling.
Social roles
鈥淭his is the first study to provide details on this type of object use,鈥� says Stephanie Bogart of in Atlanta, Georgia.
鈥淧lay is a way to prepare for adult life, whether to develop motor skills, social skills, or roles within the community. Playing with 鈥榯oys鈥� such as the sticks at Kanyawara appears have the function of developing their roles within the social group. Thus, these social roles would then determine the types of 鈥榯oys鈥� children play with.鈥�
Whereas male rhesus monkeys in captivity seem to prefer 鈥渕asculine鈥� toys such as diggers and trucks over plush dolls, wild male chimpanzees may be more in touch with their feminine sides. Young male chimps have been shown to help mothers out with infants, and adult males will play with youngsters, says Bogart.
