Chimps exposed as liars - October 16, 2007
Chimpanzees have been exposed as big cry-babies by researchers from Scotland. When chimps are attacked they scream based on the severity of the attack. However Katie Slocombe and Klaus Zuberbuhler found that some of the sneaky animals lie about how bad the attacks actually are.
“If no-one is there to help them then the screams are normal but if someone is about then they make it sound even worse than it is. This shows there is more flexibility in their vocal communication than previously thought,” Slocombe says (BBC).
In their PNAS paper the researchers identify four types of aggression, ranging from threatening behaviour to outright beating. Victims of aggression changed the acoustic structure of their screams depending on which type of aggression they experienced. Higher aggression brought forth longer, higher frequency screams. A kind of “Get your hands off of me, you damned dirty ape.”
Slocombe and Zuberbuhler say their data provide “the first systematic empirical evidence to show that nonhuman primates are able to exaggerate distress to manipulate other group members”.
Image: Getty
Comments
The bold statement "the first systematic empirical evidence to show that..." looks suspicious to me, and the conclusions look premature.
How do the authors show that their explanation is superior to alternative plausible explanations for the differences in the calls for help?
For example, if nobody is believed to be around, then the scream may just be the "reflex portion" and end there, whereas, if the ape knows that someone is around, the scream could continue past the "reflex amount" into actual communication.
Another possibility is that, when someone is around, the scream is more intense to communicate both fear and indignation ("why aren't you helping me already?"), whereas when nobody is around, the scream is about fear alone.
These possibilities occurred to me (a non-expert) after thinking about it for a few seconds. I'm sure that one can imagine other plausible explanations too. The design of the experiments would have to account for these in order to come to such bold conclusions about the motivations of nonhuman species.
While the observations in this study do sound interesting, I'm skeptical about the conclusions.
Posted by: Howard P | October 17, 2007 03:26 AM
Using "exaggeration as a form of manipulation" is a much simpler explanation than "indignation." Is there any empirical evidence of indignation in chimpanzees? And such exaggeration would be communication, ie, an attempt to manipulate others with vocalization, as opposed to just a reflex action... so the only question is, how is "systematic empirical evidence" defined? I think that is researcher-speak for "I got it first, I got it first!"
Posted by: Owein Herrmann | October 21, 2007 09:51 AM