Do chimps say “no” by shaking their heads?

When people study primate behavior with the idea of relating it to human behavior, standards of evidence often seem quite low.  There’s a lot of publicity and attention to be gotten by detecting the roots of our behavior in the other apes that are our relatives.  Who among us hasn’t been fascinated by going to the zoo, watching a chimp, and saying, “Wow–they’re so much like us!”

This is not to deny that some of our behaviors descend from those of apey ancestors. They do, of course, and Darwin was the first to write about it. But we also have culture that can rapidly transmit un-apelike behaviors across diverse groups (e.g., dancing and making music).

The attention-getting power of rather thin evidence from apes is seen in a new paper in Primates by Christel Schenider et al., “Do bonobos say NO by shaking their head?” You can already tell what the answer to their question is, for had it been “no” (i.e., chimps don’t say “no” by shaking their head), the paper wouldn’t have been published.

The authors studied infant bonobos (pygmy chimps, Pan paniscus) in three German zoos,  In 190 hours of taping bonobo infants, they observed 13 instances in which an adult chimp appeared to shake his/her head in a  human “no”-like way in association with trying to prevent an infant from doing something.  An example:

The mother and her female offspring were sitting next to each other on the ground. The offspring started crawling away toward a nearby tree trunk and proceeded to climb. The mother retrieved the infant and positioned her back to her side. The infant made continual efforts to climb the trunk, and each time the mother retrieved her. This culminated in the mother seizing the infant by the leg and shaking her head while looking toward her. The infant climbed once again, this time moving around the tree (now out of sight of the mother). After awhile, the mother got up, moved around the tree, grabbed the infant’s arm, and pulled her to the place where they originally sat. When releasing the infant the mother looked at her and shook her head once more. The mother started grooming another group member, and the infant moved toward the tree again.

You can see one of the videos at the BBC website; that and another are also at the Primates website if you have access.  Sure looks like a “no” to me!

But wait. If you read the paper, you’ll see that there were actually 49 behaviors identified as “head shakes,” and, as the authors note, “The remaining 36 (nonpreventive) head shakes were used to initiate to to maintain behavior in various contexts. These were predominantly play (n = 25), e.g., to initiate play with a group member, and affiliation (n = 6), e.g., to approach and greet a group member.”

In other words, nearly three-quarters of the head shakes were associated with affirmative rather than preventive stuff.  Further, ten of those 13 head shakes were made by a single mother, so there were only four adults involved in the behavior.  It’s hardly a pan-Pan trait!

So what do the authors conclude?  They don’t wildly extrapolate to humans, but do draw the connection:

If the use of preventive head shaking is confirmed in genus Pan, this would raise a further, more speculative, evolutionary question: Do these gestures reflect a primitive precursor of the human head shake that denotes negation? This is an intriguing possibility, but additional data along the lines indicated above will be needed to provide an informed answer.

Well, maybe, but 13 preventive head shakes and 36 “affirmative” ones doesn’t seem to me like a lot of evidence.  I’m not very impressed.

But the BBC takes it further, calling their report on this finding “Bonobo chimps filmed shaking their head to ‘say no’.” (For language freaks, shouldn’t “head” be plural?) And they say this:

The researchers are cautious to say that they cannot be sure the bonobos definitively mean ‘no’ when they shake their heads this way.

But it remains the best explanation so far.

Best explanation for what?  In how many “preventive situations” did the chimps not shake their heads in a “no-like” fashion.  And what about those other times when head-shaking was associated with positive stuff?  Does head-shaking explain that, too?

There’s one other matter.  Do all humans really say “no” by shaking their heads?  Many societies do this, but I’m not so sure the behavior is a cultural universal.

During the months I spent in India, I learned that Indian head-gestures for “yes” and “no” are very different from ours. When the head is drawn back upwards, looking like part of a “yes” nod, it really means “no.” A side-to-side waggling, however—(the “Indian head bob“)—which looks much like our “no”, means “yes.” It took me a while to learn that when I thought I was being refused, I wasn’t.

And, in fact, the chimp’s head shake in the BBC video looks very much like the “nodding” and affirmative Indian bobble:

Apparently the same gestures hold in Bulgaria:

Schneider admits this cultural variation in her interview with the BBC, but the authors sure don’t discuss it in the Primates paper, saying only that “[head shaking] is generally associated with an explicit or implicit negative connotation in many parts of the world.”  And we simply have no idea how early hominins used their heads to gesture “no,” or whether what generality there is among cultures in the “no-shake” might be based on cultural inheritance instead of being—as the BBC suggests—”hardwired” in humans.

Of course very few people who read the BBC report will read the original paper.  Pity.

h/t: Matthew Cobb, Otter

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Schneider, C., J. Call and K. Liebal.  2010.  Do bonobos say NO by shaking their head?  Primates online, doi: 10.1007/s10329-010-0198-2