Monday, December 20, 2010

On Sticks And Chimpanzees

Mother Jones discusses a study which finds that female young chimpanzees carry sticks much, much more often than male young chimpanzees. The study argues that this means the sticks are dolls and that the behavioral differences tell us that there is a gender difference in childhood play in chimpanzees in one chimpanzee community.

But these results will ultimately be applied human sex differences in play and how that prepares us to our later gender roles in the society: Girls play with dolls, boys play with trucks and cars, all this is innate and explains the absence of women among American presidents, say.

From the study abstract:

Sex differences in children's toy play are robust and similar across cultures. They include girls tending to play more with dolls and boys more with wheeled toys and pretend weaponry. This pattern is explained by socialization by elders and peers, male rejection of opposite-sex behavior and innate sex differences in activity preferences that are facilitated by specific toys. Evidence for biological factors is controversial but mounting. For instance, girls who have been exposed to high fetal androgen levels are known to make relatively masculine toy choices. Also, when presented with sex-stereotyped human toys, captive female monkeys play more with typically feminine toys, whereas male monkeys play more with masculine toys. In human and nonhuman primates, juvenile females demonstrate a greater interest in infants, and males in rough-and-tumble play. This sex difference in activity preferences parallels adult behavior and may contribute to differences in toy play. Here, we present the first evidence of sex differences in use of play objects in a wild primate, in chimpanzees (Pan troglodytes). We find that juveniles tend to carry sticks in a manner suggestive of rudimentary doll play and, as in children and captive monkeys, this behavior is more common in females than in males.
Wow. That's it, then.

Well, not quite. First, the nature-vs-nurture argument, in the versus sense, is outdated and incorrect. The actual way these things work is much more complicated and interactive.

Second, studies of chimpanzees in prison (cages) introduces a human influence (difficult to control for) in their environment and doesn't really study them in their actual habitat.

Third, those findings about the chimpanzees in the wild? They only apply to one chimpanzee community:

The findings link this play to adult behavior, since female carry infants more than 99 percent of the time and males less than 1 percent of the time—making this a seemingly clear case of nature over nurture. But there's little evidence of stick-carrying behavior in other chimpanzee communities. So the Kibale chimps appear to be copying a local behavioral tradition—making this a case of nurture over nature. Put them together, and you get a clear case of biological and social influences entwining.
You know what this sounds like to me? It sounds like cultural evolution. If we insist on using the nature-vs-nurture idiom, the lack of stick playing in other chimpanzee communities would, in fact, rule against nature, never mind whether male and female chimpanzees play with sticks at different rates in one particular community. The young chimpanzees would observe the gender norms of their group and follow those.

Indeed, I suspect that gender identification in early childhood may be the engine that drives many of the toy choices rather than some innate interest in one particular type of toy. Or at least it's a valid alternative theory, because any particular toy could be played with in many different ways.

I'm not writing this post because, as the abstract says, discussing innate differences in human play is somehow "controversial," but because I suspect we are stuck at the level of far-too simple-and-shallow explanations and because most of those end up being used in the propaganda sense. So you will keep hearing that even chimp girls play with dolls and chimp boys with cars!
Thanks to trifecta for the link.