WASHINGTON — Primates may have evolved color vision not to find the ripest, tastiest fruit but to detect that tell-tale blush on someone else's rump, U.S. researchers reported Thursday.
The cone structures in the eye that help detect color seem exquisitely tuned to skin tones, the team at the California Institute of Technology reports.
"For a hundred years, we've thought that color vision was for finding the right fruit to eat when it was ripe," Mark Changizi, a theoretical neurobiologist and postdoctoral researcher at Caltech who led the study, said in a statement.
"But if you look at the variety of diets of all the primates having trichromat (three-color) vision, the evidence is not overwhelming."
Instead, Changizi and colleagues report in the journal Biology Letters, the system seems adapted especially to find the colors prevalent in primate skins — notably changes due to how much oxygenated hemoglobin is in the blood.
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In contrast, bees have four color cones that are evenly spread across the visible spectrum, with the high-frequency end extending into the ultraviolet. Birds have three color cones that are also evenly distributed in the visible spectrum.
And the three-cone system can help a primate tell not only if a potential partner is having a rush of emotion in 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 said. That may be why humans value rosy cheeks, he said.
