Women may be able to see more subtle shades of red than men, research suggests.
Women may have keener vision
Arizona State University scientists have discovered the gene which allows people to see the colour red comes in an unusually high number of variations.
The gene sits on the X chromosome, which means women have two copies, and men just one.
The researchers believe this could mean that women may have a more acute perception of the red-orange spectrum.
The researchers, who report their findings in the American Journal of Human Genetics, analysed the DNA of 236 people from around the world.
They found no less than 85 variations of the key gene, called OPN1LW. This is about three times the usual number of variations found in most genes.
It is thought that the red gene routinely swaps bits of genetic material with its neighbour on the X chromosome, which controls perception of the colour green.
Sometimes this exchange goes wrong and results in a defect that causes color
However, while an estimated 8% men are colour-blind, few women have the condition.
This is because the odds are they will have at least one good copy of the red and green genes.
Lead researcher Dr Brian Verrelli, who carried out the study with and Dr Sarah
Tishkoff, who is at the University of Maryland, said the gene variations had probably been around for a long time, possibly hundreds of thousands of years.
He told BBC News Online: "If it has been around this long, this suggests that it was beneficial and kept in the population by natural selection.
"Females may have historically been better at gathering fruits and other food items because of their better colour discrimination in the red range of colour.