Science Spin January 2007

Dancing, a good way to get a mate?

The Artic Monkeys' anthem "I Bet You Look Good On The Dancefloor" has acquired an unexpected resonance in the world of evolutionary biology. Research reported in Nature recently uncovers a relationship between the dancing skills of a potential suitor and their chances of being sexually selected.

Darwin

The two cornerstones of evolutionary theory, as first articulated by Charles Darwin, are the selective forces; natural selection and sexual selection.

In Darwinian theory, selection signifies the process by which a variable trait is selectively passed on to the next generation by giving its holder a better chance of being able to reproduce. The distinction comes when we examine more closely the reasons why this trait gave its holder an advantage.

Natural selection deals with the traits that give us an advantage in producing offspring by virtue of the fact that we have managed to survive to sexual maturity and can therefore pass that characteristic on.

Sexual selection, on the other hand, is less a story of life and death but more a tale of one sex trying to impress the other. If a particular trait sparks a fancy in the opposite sex and gives the possessor a greater chance of reproducing solely because of the fact that the trait it possesses catches the eye of a member of the opposite sex, then this trait is said to be sexually selected.

Sometimes sexual selection can lead evolution down surprising and whimsical paths. Take, for example, the manakin, a small sparrow-sized bird of South and Central America. In order to impress the female members of the species, the males perform an elaborate Michael Jackson-esque 'moonwalk' dance. The video clip of this endearing little character has to be seen to be believed.

A very important fact must be highlighted at this stage. No matter how trivial the trait being sexually selected for, the trait must always provide at least a neutral if not a positive advantage for natural selection. If the trait chosen is in any way disadvantageous in the battle to be naturally selected it will quickly be weeded out by the unforgiving and merciless process of evolution.

Humans

What do we know about dancing and sexual selection in humans? Do those amongst us who really do 'look good on the dancefloor' have an advantage over those of us in the 'two left feet' brigade? A team of American scientists led by Robert Trivers set out to address this question. They began by modelling the dancing motions of 183 Jamaicans, a society in which dance plays an important role.

The experiment posed the question: Are people who are inherently more attractive, or 'fitter' in evolutionary speak, better dancers as judged by the opposite sex? What do we mean by 'fitness' and how might we measure it? One way to do this is to measure body symmetry. Many studies have shown that the degree of body symmetry is related to the 'fitness' of the individual, in other words, the more symmetrical an organism's body is, the more likely that particular organism is to be healthy, live longer and produce more offspring.

To separate the dancing ability of the subjects from other factors that might influence their chances of being sexually selected, the dancer's movements were modelled using a computer programme. The resulting video shows a crash-test dummy- like character accurately shadowing the dance motion of a particular dancer but who is completely devoid of possible interfering factors like facial appearance or physique.

The scientists found strong positive associations between body symmetry and dancing ability and they found that this association was stronger in men than in women. In other words they found that women rated 'fitter', inherently healthier men, as judged by body symmetry measurements, to be better dancers than men who had low body symmetry scores.

The fact that women's strong preference for 'fitter' men was not equally reciprocated by men rating women's dancing is to be expected in a species like our own, in which mothers invest more energy in the rearing of their offspring than fathers do and are, therefore, expected to be more selective in their choice of mate.

So, is there any hope for those of us who inelegantly plod around the dancefloor? It seems that the jury is still out but maybe I'll enquire about those dance classes all the same.