Men might be from Mars and women from Venus, but a new study on flies suggests that they are both equipped with a largely unisex brain.

Male fruit flies usually sing to attract females, vibrating one wing to produce a distinctive sound.

Previous studies had identified the neurons responsible for the male singing behaviour. However, it seemed that females had that circuit too, even though they don't sing.

Now, by artificially triggering the neurons responsible for singing, the researchers made female flies play their first tune.

" You might expect that the brains of the two sexes would be built differently, but that does not seem to be the case," said Gero Miesenbock, formerly of Yale University and now at the University of Oxford.

"Instead, it appears there is a largely bisexual or 'unisex brain' with a few critical switches that make the difference between male and female behaviour.

" The mystery at the root of our study is the neuronal basis of differences in male and female behaviour. Anatomically, the differences are subtle. How is it that the neural equipment is so similar, but the sexes behave so differently," he added.

In order to answer this question, the researchers used a special technique they developed in which the singing circuit could be turned on in either males or females with a simple flash of light.

First, they confirmed the connection between that circuit and the courting behaviour in males.

When they triggered the same circuit in members of the opposite sex, the otherwise quiet female flies immediately began acting like males.

"They just stuck out their wing and started singing," Miesenbock said.

However, the researchers found that the rookie females did sing off key.

" If you look carefully, the females do sound different. They have a different pitch and rhythm and aren't as well controlled," he said.

He believes that those distinctions probably stem from real, if subtle, differences between the male and female brains, not from a lack of practice.

The findings suggest that the circuits for maleness are present but dormant in females.

"Female flies have the program, but they seem to lack the activating command. Either way, the principle is the same [in flies and mice]: males and females are not as different as you might think," Miesenbock said.

According to the researchers, the findings suggest that flies must harbour key nodes or 'master switches' that set the whole system to the male or female mode.Their next step is to find those controls.