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Monday, March 13, 2006

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Colour vision and sexual signalling in primates, including humans

From a Caltech press release:

QUOTE

In fact, trichromat vision is sensitive not only for the perception of these subtle changes in color, but also for the perception of the absence or presence of blood. As a result, primates with trichromat vision are not only able to tell if a potential partner is having a rush of emotion due to the anticipation of mating, but also if an enemy's blood has drained out of his face due to fear.

"Also, ecologically, when you're more oxygenated, you're in better shape," Changizi adds, explaining that a naturally rosy complexion might be a positive thing for purposes of courtship.

Adding to the confidence of the hypothesis is the fact that the old-world trichromats tend to be bare-faced and bare-butted as well. "There's no sense in being able to see the slight color variations in skin if you can't see the skin," Changizi says. "And what we find is that the trichromats have bare spots on their faces, while the dichromats have furry faces."


"This could connect up with why we're the 'naked ape,'" he concludes. The few human spots that are not capable of signaling, because they are in secluded regions, tend to be hairy-such as the top of the head, the armpits, and the crotch. And when the groin occasionally does tend to exhibit bare skin, it occurs in circumstances in which a potential mate may be able to see that region.

"Our speculation is that the newly bare spots are for color signaling."


UNQUOTE

A weakness in this theory is that early humans - being Africans - presumably had black skin. One of the few exceptions seen in modern Africans are the pink mucous membranes made visible by the characteristic eversion of the lips in many Africans. I discuss the possible role of these pink lips in signalling health here. I presented this idea to a recent annual meeting of the Australasian Society for Human Biology.

Julian

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