You might call it a tale of "monkey see, monkey do." 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.
apes and Old World monkeys, such as macaques and leaf monkeys, all have
trichromatic vision, which allows these primates 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.
Now a new study published online this week in American Naturalist by
Ohio University researchers Andre Fernandez and Molly Morris 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
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
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.
"Neuroscience research has found some
evidence of a perceptual bias for more brilliant colors," said
Fernandez, an Ohio University doctoral student. "So, it is reasonable
for primates with trichromatic color vision to respond more when they
see bright colors."
So while foraging may have initially sparked red color vision, the new ability was likely "recruited" for social purposes.
looks like red skin and hair became a sexual preference," said Morris,
a fish biologist who studies how physical traits such as coloring
evolve through sexual selection. "So while the benefits in terms of
eating may not apply anymore, the (red-color) vision in some groups is
now relevant in social terms."
Ohio University. May 2007.