A hermaphrodite worm. (Jamie White, University of Utah)

New Delhi, Oct. 26: Scientists have genetically tweaked the brains of worms to get females to seek out other females for mating in experiments that have bolstered the evidence for a biological basis for sexual preferences.

US biologists selectively turned on a gene associated with maleness in the brains of female worms and found that these altered worms were attracted to the same sex. The findings were published yesterday in the journal Current Biology.

“They look like girls, but act and think like boys,” said Jamie White, a researcher at the University of Utah, lead author of the study and member of a group trying to explore how the brain generates behaviour.

A number of previous studies, including similar experiments in fruit flies and mice, have provided strong evidence of a genetic component to sexual preferences.

“There is evidence for genetic component to human sexual orientation. By studying worms, we hope to discover principles through which we can understand the basis of human (sexual) behaviour better,” White told The Telegraph in an interview.

Two years ago, neurobiologists in Austria had shown that altering a protein in the brains of fruit flies could get female flies to display courtship behaviour directed at other females — remarkably similar to that shown by male flies.

But the relative simplicity of the worm brain has allowed scientists to probe details of mate-seeking behaviour at an unprecedented level.

“We can identify exactly which cells in the male brain are sensing females and we can then study the circuit that is making a decision and executing mate-seeking,” said Eric Jorgensen, team leader and scientific director of the Brain Institute at the University of Utah.

The Utah team worked on a worm called C. elegans, which is just a millimetre in length, is found in soil and has no eyes but uses smell for mating behaviour.

The female worms which produce offspring are actually hermaphrodites with male and female reproductive organs.

The researchers, however, caution that it is unclear what the findings mean for human sexual orientation.

“The findings underscore the importance of genes in sexual orientation. But humans are complex and possess free will — we are not mere automatons directed by genes. At some level, individuals make sexual choices,” Jorgensen said.

Human behaviour, the researchers point out, is also influenced by culture and society.