A gene that could explain how humans pick up powerful chemical signals called pheromones may have been pinpointed for the first time.The discovery promises to give scientists a new understanding of our basic instincts.

Pheromones are known to trigger physical responses including sexual arousal and defensive behaviour in many species of insects, fish and animals.

There has long been speculation that humans may also use these chemicals to communicate instinctive urges.

Women living together often synchronise their menstrual cycles because they secrete an odourless chemical in underarm sweat.

But until now scientists have not been able to explain how and where in the body the chemicals are picked up and their messages passed to the brain.

Special organ

Many animals, including mice, rabbits and pigs, have a special organ called the vomeronasal organ (VNO).

This relays chemical signals directly to the most primitive centres of the brain, stimulating instinctive reactions.

In human embryos these organs exist but they appear to perform no function after birth.

Now, scientists at Rockefeller University in New York and Yale University in Connecticut believe they have found a gene which may create pheromone receptors.

A receptor is an area on a cell that binds to specific molecules.

Called V1RL1, the gene resembles no other type of mammalian gene and bears a strong similarity to those thought to create pheromone receptors in rats and mice.

"People have taken an anatomical approach to the issue in the past. This is the first attempt to look at the molecular biology," said Dr Peter Mombaerts from Rockefeller University in the journal Nature Genetics.

Ancient clues

Dr Mombaerts and his colleagues also found seven related snippets of DNA which should produce a protein but appear to have been turned off at some stage in their evolution.

Why these "pseudogenes" exist is a mystery. One possible explanation could be that in their distant evolutionary past humans made more use of pheromones than they do now.

Much work still needs to be done to prove V1RL1 is a gene and does create pheromone receptors.

A biotechnology company called Senomyx in California is looking at how the gene may work and which aspects of human behaviour are controlled by pheromones.

Some ethicists are worried research could lead to pheromone abuse. Carefully targeted artifical pheromones could be misused to modify human behaviour in advertising, politics and even warfare.