Seeing colours differently

Normal variation in red opsin gene, especially in women give them a better perception of colours.

It's long been known that color blindness is caused, usually in men, by changes in the red and green opsin genes, the genes that enable humans to perceive colour.

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But a new study of randomly selected people from geographically diverse populations shows that normal variation in the red opsin gene may have been maintained by natural selection to give humans, especially women, a better perception of colour.

The exchange of genetic material between the red and green colour vision genes results in large amounts of genetic variation. However, this exchange can also sometimes go awry and result in colour blindness. In fact, eight per cent of the world's men are colour blind.

Those variations may have been especially important, researchers speculate, in a time when humans were hunter-gatherers. Enhanced colour perception would have allowed women, who were traditionally gatherers to better discriminate among coloured fruits, insects and background foliage.

The chromosomal difference between women and men is the key to why variation of the gene may have different results in women and men. Women have two X-chromosomes; men have only one X-chromosome and one Y-chromosome. Because this colour vision gene resides on the X-chromosome, rare detrimental changes at this gene cause colour-blindness in males, whereas females are likely to have at least one good copy of the gene.