Saturday, May 26, 2007

Better to Give than to Receive

One of the great mysteries of evolutionary biology is altruistic behavior. Why should organisms reduce their own fitness for the benefit of others? For example, social grooming (depicted) appears to have no direct benefit for the groomer. The standard explanations cite reciprocity (i.e., I'll pick the nits off your back, if you pick the nits off mine) and social enhancement (e.g., alliance building). What's not often considered is the possibility that the behavior is directly beneficial for the actor, and that's exactly what a new paper by Shutt et al. in Biology Letters suggests. "In this study, we quantified grooming behaviour and physiological stress (assessed by faecal glucocorticoid analysis) in free-ranging Barbary macaques, Macaca sylvanus. Our results indicate that it is the giving rather than the receiving of grooming that is associated with lower stress levels."

Of course, I say! No wonder we find petting our pets so enjoyable and relaxing. It probably simulates social grooming and reduces our stress hormones.

Photo by Crystalline Radical.


  1. Do you believe there was a time when macaques did not engage in grooming behavior? Do you believe that a mutation arose in that population of primitive macaques causing them to start grooming and this new allele provided such a selective advantage that it swept to fixation?

    If you don't believe in those things then would you be kind enough to explain the scenario that you do believe in? Remember, you have to explain the things you're claiming to be true; namely that the specific behavior of grooming arose in a population that didn't have it and it proved to have a selective advantage.

    The problem with most of these just-so stories is that nobody every takes the time to think through the implications. (Like what kind of gene could be responsible for grooming behavior.) Let's give it a shot, okay?

    I think grooming is an epiphenomenon that arises out of complex behavior associated with living in a close community. I would be very surprised to find a gene controlling grooming behavior that didn't affect lots of other things as well. If I'm right then it makes no sense at all to talk about grooming as an adaptation.

  2. Your argument hearkens back to the great EO Wilson vs. Gould/Lewontin debates. Here's a response from the Wilsonian school:

    Driscoll, C. 2004. Can Behaviors Be Adaptations? Philosophy of Science, 71:16–35.

  3. I would love to read that Driscoll paper - do you have it as a pdf? I have access to NO online journals except Science and the open ones. . . :(