Researchers at Ohio University have found that after primates evolved the ability to see red, they began to develop red and orange skin and hair.

Humans, apes and Old World monkeys, such as macaques and leaf monkeys, all have trichromatic vision, which allow them to distinguish between blue, green and red colors. Primatologists have disagreed about whether this type of color vision initially evolved to help early primates forage for ripe fruit and young, red leaves among green foliage or evolved to help them select mates. 

"Neuroscience research has found some evidence of a perceptual bias for more brilliant colors," said Andre Fernandez, an Ohio University doctoral student. "So, it is reasonable for primates with trichromatic color vision to respond more when they see bright colors."

"It looks like red skin and hair became a sexual preference," said Molly Morris, a fish biologist who studies how physical traits such as coloring evolve through sexual selection. 

Their new rules out an initial advantage for mating and suggests that red-color vision evolved for non-social purposes, possibly foraging. But once developed, trichromaticism drove the evolution of red skin and hair through sexual selection.

Fernandez, the study's lead author, first began to question the strict correlation of food choice and color vision while studying howler monkeys in Costa Rica. He recently compiled data on the color vision, social and sexual habits and red skin and pelage of 203 different primate species.

The researchers then used a phylogenetic tree representing the evolutionary relationships among all the primate species under study to test hypotheses about the order in which the traits of red color vision, gregariousness (highly social behavior) and red coloring evolved. By comparing the traits of individual species in this evolutionary context, Fernandez and Morris could statistically deduce the probability of their ancestors having the same traits, as well if any of the traits were correlated with one another.

They found that the species that could discern red and orange hues were more likely to develop red and orange skin and hair, as well as highly social habits that make it easier to visually compare mates. In fact, the more social the trichromats are, the more red coloring they show.

Source: Ohio University