Sexual selection: Darwin does Jamaica.

A study of Jamaicans dancing finds that some of Darwin's ideas about the evolution of animal courtship apply to people. Darwin himself suggested that dance has been shaped by sexual selection, an evolutionary process that favors showy traits, such as peacock tails, that attract mates. The trait doesn't have to boost survival and may even be detrimental to long life, but it has to say "sexy."

For dance to serve as an example of sexual selection, the performance has to reveal something about the innate physical quality of the dancer. To test for such hints, scientists turned to people in Southfield, Jamaica, who had been tested for physical symmetry in a long-term study by Robert Trivers of Rutgers University in New Brunswick, N.J. A controversial theory has argued that asymmetries, say in ear size, indicate developmental shortcomings that make the individual get sick more easily and reproduce less successfully than a symmetrical person.

William Brown and Lee Cronk of Rutgers and their colleagues used cameras to track laser reflectors fastened on people and then made 40 animations of young Jamaicans dancing to the same pop song (see video at http:// grail.es.washington.edu/projects/ dance-symmetry/index.html). The animations didn't reveal the dancer. The researchers then asked 155 other young Jamaican men and women to rate how well the animated characters danced.

Observers ranked the dances most highly when the person behind the animations belonged to the high-symmetry group, Brown and his colleagues, including Trivers, report in the Dec. 22/29, 2005 Nature. So, a head-turning dance style may be a good way to choose a partner.--S.M