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.