This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Today we present the IgNobel prize in ANATOMY, presented to de Waal and Pokorny. They were very pleased to win the IgNobel this year, noting especially that scientists always take themselves so seriously (sigh, yeah, we do), and it's nice to have a little fun once in a while.
de Waal and Pokorny. "Faces and behinds: chimpanzee sex preception'' Advanced science letters, 2008.
So what so great about chimp butts? Well, it's not about the butts specifically, it's more about how the chimps recognize each other. We know that chimps and other monkeys and apes do recognize others of their species, and can reliably associate facial similarity between offspring and mothers, even if they don't know the mother. The question is, how do they do it? Can they tell from the faces alone, as humans can (even without hair or other markers), who is male and female? And if they can do it, what does that mean?
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This means you need some chimps. And some photos of chimp butts.
The authors took 6 chimps (3 male, 3 female) who had been trained to use a joystick and a computer screen. They brought each chimp in and handed them the joystick. Then they had them play a "game" of match to sample. This is a very commonly used behavioral test. You present an animal (or a human) with a stimulus (say, a red box), then a little bit of time goes by, and then the participant is presented with two options, a red box and a blue circle. They have to select the one that matched the previous sample. If they pick the red box, they get a reward.
In this case, the authors changed the study up a little. This time, the sample, what would have been the red box, is a chimp's butt, complete with visible genitals. Then the chimps were presented with two options, a male chimp face and a female chimp face, or two chimp faces of the same sex, one of which possessed the previously shown derriere. The faces and butts represented chimps that the subjects did not did not know personally. The whole thing looks like this.
(For those unfamiliar with chimp dating sites, the male face is on the right)
What they found that was chimps could easily match the sample butt to the sample face and showed good sex matching, but ONLY in the case of chimps that they knew personally. When it came to the random Facebook friend request, the chimps couldn't match butt to face.
This is actually an important finding for several reasons. First, the chimps knew the photos. They knew that those photos represented fellow chimps they knew (or did not). But it also suggests that image alone isn't enough for the chimp to determine the gender of the individual (though there's always the chance the chimps being tested didn't get the concept). A picture alone doesn't help, they require the behavior of the fellow chimp, getting to know them, in order to easily identify gender. The authors refer to this as a "gender construct", because it means that chimps require experience of other chimps to perform sex discrimination.
I think it's very cool that chimps can recognize photos and know that those represent other chimps. But this makes me think, if they wanted to determine FACIAL recognition, they might have been better off starting with the faces, and then presenting the butts. Like "here's a female face, is this her butt? Y/N". Rather than "here is a butt, is it a female? Y/N". This might allow you to look at results for both conditioning, face first and butt first, to try and more clearly differentiate identification of gender and identification of a known chimp.
But it's still a fun study, and I had to ask...has it been tested in humans? No, they said, it would be a tough one for approval. But I personally bet they'd have a lot of volunteers.