Do you see the number 15 here? People with color blindness cannot (Credit: Courtesy of Pseudoisochromatic 24 Plate, Vision Training Products, Inc.)

Color blindness is not always a disadvantage, according to University of Calgary primatologist Amanda Melin and her colleagues,who found that wild color-blind capuchins in Costa Rica are better at detecting camouflaged insects than individuals with broader color vision.

To determine how color vision affects insect hunting, the researchers used DNA samples to distinguish capuchins that were partially color-blind from those with a wider spectrum of color vision. Observations of capuchins foraging for surface-dwelling insects showed that color-blind capuchins made nearly 20 insect-capture attempts per hour, compared with only about 16 for those with normal color vision.

One possible explanation for the color-blind advantage is that a reduction in color signals makes the differences in texture and brightness more apparent, so it’s easier to see past color camouflage, says Melin.

Could similar effects have caused color blindness to arise and persist in humans? It’s hard to tell. “Two things could have happened;there may have actually been some advantage for color-blind early humans—they might have been hunting animals with camouflage,” says Melin. “Or selection pressure for maintaining color vision could have relaxed because it wasn’t a big advantage in the habitat or types of hunting used at the time.”