HENRY

Why do primates have color vision? One of the leading theories over the last few years is that primates evolved trichromatic color vision to better detect fruits (generally red or orange colored) from leaves (primarily green). However, others have argued that the cause was to enhance intra-specific signalling, primarily to recognise the reddened skin regions which can signal sexual arousal/fecundity.

A study out in American Naturalist, Sexual Selection and Trichromatic Color Vision in Primates: Statistical Support for the Preexisting-Bias Hypothesis by Fernandez and Morris, investigates this. Using a large phylogeny of primates, the authors reconstructed the characteristics in question on the tree, and show that trichromatic color vision evolved deep in the tree (prior to the Tarsiidae-platyrrhine-catarrhine split), which is before the evolution of gregarious mating systems (which appear to have arisen prior to the Old World monkey split).

These results suggest that color vision evolved first, but then became exapted for intraspecific communication. What’s more, the use of reddened skin color as a sexual marker is more likely to evolve in the primate lineages with color vision and lead to gregarious social mating systems. That is, color vision appears to have played a role in allowing gregarious mating systems to have evolved in primates.

The abstract:

The evolution of trichromatic color vision in primates may improve foraging performance as well as intraspecific communication; however, the context in which color vision initially evolved is unknown. We statistically examined the hypothesis that trichromatic color vision in primates represents a preexisting bias for the evolution of red coloration (pelage and/or skin) through sexual selection. Our analyses show that trichromatic color vision evolved before red pelage and red skin, as well as before gregarious mating systems that would promote sexual selection for visual traits and other forms of intraspecific communication via red traits. We also determined that both red pelage and red skin were more likely to evolve in the presence of color vision and mating systems that promote sexual selection. These results provide statistical support for the hypothesis that trichromatic color vision in primates evolved in a context other than intraspecific communication with red traits, most likely foraging performance, but, once evolved, represented a preexisting bias that promoted the evolution of red traits through sexual selection.