Symmetry is not just for particle physicists

Posted 30 December 2005 by Andre under Hot off the Press

Symmetry plays an important, some would say paramount, role in fundamental physics. It’s success as a unifying principle in physics is impressive, but symmetry isn’t only important for keeping the universe running smoothly. A couple of recent articles in Nature show how symmetry crops up in behaviour in two totally different ways.

The first one uses an image capture system to analyze the dance moves of Jamaican youth. By using digitized dancing models the authors eliminated any bias due to other aspects of the dancers’ appearance and they discovered that symmetric people dance better than more asymmetric people as judged by their peers. This lends credence to the idea “that dance is a sexually selected courtship signal” in humans since perceived dance skill correlates with the youths’ symmetry which in turn correlates with fitness. In the authors’ words:

[An] indicator of quality is degree of fluctuating asymmetry (FA), because it is inversely correlated with degree of developmental stability, which is an organism’s ability to reach an adaptive end point despite ontogenetic perturbations. Across diverse taxa, increased FA is associated with increased morbidity, mortality, poor fecundity and other variables linked to natural and sexual selection. Most germane to the hypothesis that dance reveals underlying developmental stability is evidence that reduced fluctuating asymmetry is associated with locomotory traits or their functional effectiveness in several species, including humans.

To measure the degree of “fluctuating asymmetry” they used Vernier calipers to measure the length of various left and right parts of their subjects’ anatomy including fingers and ears. So next time you’re wondering why you can’t pick up the latest dance moves, break out the calipers and see if one of your ears is significantly bigger than the other. As an aside, in their methods section they reported that these features were measured to an accuracy of 0.01 mm. I’m sorry, but that’s just not true. Ears and fingers are soft and are not even well defined on that scale (where exactly does your finger end and the rest of your hand begin?). I would hate to be the grad student responsible for carefully reading and writing down those measurements to that many (useless) decimal places while my supervisor was out doing the important field research in clubs to determine which song was “popular at the time in Jamaican youth culture”!

For more details, including some cool videos of the digitized dancers, see the group’s website.

The other recent paper dealing with symmetry and behaviour involves chiral elephant pheromones. I talked about chirality in biology in an earlier post, but this was an application I had certainly never heard of before.

Musth in male elephants is an annual period of heightened sexual activity and aggression that is linked to physical, sexual and social maturation. It is mediated by the release of chemical signals such as the pheromone frontalin, which exists in two chiral forms (molecular mirror images, or enantiomers). Here we show that enantiomers of frontalin are released by Asian elephants in a specific ratio that depends on the animal’s age and stage of musth, and that different responses are elicited in male and female conspecifics when the ratio alters.

Excellent stuff! The idea that pheromones play a role in human behaviour is also a fascinating, if controversial, idea.