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Updated: Jul 18, 2026

The Gateway to the Brain: Dissecting the Primate Eye
Published on: May 27, 2009
Bare skin, blood and the evolution of primate colour vision
Mark A Changizi1, Qiong Zhang, Shinsuke Shimojo
1California Institute of Biology, Sloan-Swartz Center for Theoretical Neurobiology, MC 139-74, Caltech, Pasadena, CA 91125, USA. changizi@caltech.edu
Abstract:
We investigate the hypothesis that colour vision in primates was selected for discriminating the spectral modulations on the skin of conspecifics, presumably for the purpose of discriminating emotional states, socio-sexual signals and threat displays. Here we show that, consistent with this hypothesis, there are two dimensions of skin spectral modulations, and trichromats but not dichromats are sensitive to each. Furthermore, the M and L cone maximum sensitivities for routine trichromats are optimized for discriminating variations in blood oxygen saturation, one of the two blood-related dimensions determining skin reflectance. We also show that, consistent with the hypothesis, trichromat primates tend to be bare faced.
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