Color vision

In humans, color blindness is much more common in males than females (7% vs. 0.4%, according to Montgomery, 1997). Jordan and Mallon (1993) suggest that there may be some women who are tetrachromats: they may see in four wavelengths, instead of the three that most humans get. Color vision is dependent on cone cells in the eye, and the expression of cone cells seems to be programmed on the X-chromosome. Glenn Zorpette's 2000 article "Searching for Madam Tetrachromat" goes further into why tetrachromacy is only expected in women.

An extra color channel in females is hardly unheard of. Gerald Jacobs (2004) found that most squirrel monkeys are dichromats (2 colors). The only squirrel monkeys that were trichromats (3 colors) were some of the females. Mark Prescott (2006) suggests that this is evolutionarily related to the brightly colored markings on some male new world monkeys -- the females can distinguish them, but their male competitors can not.

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I think everyone can find something to be excited about in tetrachromacy. My partner suggested titling today's piece "D00d! Chicks be stealin' yer conez!" and then started babbling about how great a "hidden roles" game you could make out of color blindness. What I find interesting about it is the fact that most of what women tell me that they're better than men at is perception -- they see more. Tetrachromacy, however rare, may be a case where this is literally true.

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