I will be hosting the Four Stone Hearth on 1/05/11. Please send my your submissions! In the meantime, I am looking for hosts for dates in February and March. If you are interested in hosting drop me a line (my email address is on the “About” tab).
Current Biology has and interesting paper called Sex differences in chimpanzees’ use of sticks as play objects resemble those of children. The paper, by Kahlenberg and Wrangham, reports on male and female play with sticks. The study involved chimpanzees of the Kanyawara community at Kibale National Park in Uganda.
Chimps use sticks for a number of ways: as probes, to termite fish or ant dip, in aggressive displays, and in the behavior that is the subject of the paper. From Kahlenberg and Wrangham 2010:
Stick-carrying consisted of holding or cradling detached sticks (median length, 36 cm; median weight, 112 g; n = 6 recovered sticks). The juveniles carried pieces of bark, small logs or woody vine, with their hand or mouth, underarm or, most commonly, tucked between the abdomen and thigh (Supplemental information). Individuals carried sticks for periods of one minute to more than four hours during which they rested, walked, climbed, slept and fed as usual. From all-events recording in chimpanzee parties from 1993 to 2006 we found that stick-carrying represented 38.9% of total stick use observations (n = 301), and 10.0% of object use observations (n = 1170). Regular stick-carrying has no discernible function and has not been reported from other chimpanzee studies …, even where stick use has been carefully documented for many years…
My first thought on reading this was that females, in other populations of chimpanzees, engaged in quite a bit more termite fishing and ant dipping than males and that this was a reflection of that. Kahlenberg and Wrangham 2010 discuss this possibility and dismiss it because this kind of stick-carrying ceases with motherhood and carried sticks were regularly taken into day nests and played with (unlike sticks used for other activities). Additionally, some forms of stick use are male biased (mainly in aggressive displays) and male chimpanzees used leaves to wipe their bodies more frequently than females. Consequently, Kahlenberg and Wrangham argue that this behavior is learned from other juveniles and represents a juvenile tradition of a type reported only in humans and go on to say that:
The sex difference in stick-carrying in juvenile Kanyawara chimpanzees arises without any teaching by adults and is consistent with practice for
adult roles. Our findings suggest that a similar sex difference could have occurred in the human and pre-human lineage at least since our common ancestry with chimpanzees, well before direct socialization became an important influence.
I have some reservations about this last bit, but will have to think about it further. At any rate it is an interesting article that presents a previously unknown social learning behavior among chimpanzees at Kibale (and so far it has only been observed at Kibale).