Colorblind Hunter-Gatherers

Evidence That Men And Women Literally See The World Differently 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 color. 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 color. ... Those variations may have been especially important, Verrelli and Tishkoff speculate, in a time when humans were hunter-gatherers. Enhanced color perception would have allowed women, who were traditionally gatherers, to better discriminate among colored fruits, insects and background foliage. ... The chromosomal difference between women and men is the key to why variation of the OPN1LW 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 color vision gene resides on the X-chromosome, rare detrimental changes at this gene cause color-blindness in males, whereas females are likely to have at least one good copy of the gene. -- via Feministing

The headline to this article is a nice example of what happens when people try too hard to make science interesting to the lay public -- a subtle difference in color perception with a great deal of intra-sex variability is inflated into a men-are-from-mars-women-are-from-venus issue. The substance incorporates a nice bit of reverse sociobiology, in which a just-so-story about human society is used to explain something biological.

On the one hand, I'm glad that the issue of gender roles in hunter-gatherer society, and the contribution of women to their subsistence, has become part of the public consciousness. On the other hand, it's frequently misused, as we see here.

The problem is that it's too simple to say that hunter-gatherer men hunt while the women gather. It would be more accurate to say* that adult hunter-gatherer men are the sole hunters of big game, while hunter-gatherer women and children of both sexes do most of the socially-shared gathering. Hunter-gatherer males do quite a bit of the fruit gathering that the authors claim requires better color vision. They do it all the time when they're children (when selection pressure would seem to be the greatest, since death as a child prevents you from ever having any offspring). And they gather extensively to feed themselves while out on the hunt, since big game would only be killed once a week or so.

I'm no geneticist, but it seems to me that the sex difference in color perception is not an adaptation. It's just a side-effect of the fact that color perception is controlled by the X chromosome, and men only happen to have one of those.

*Insofar as contemporary tropical hunter-gatherers give us any indication of how our ancestors lived.