Abstract: How the World Became Coloured—The Evolution of Hue Perception In Primates
Nearly 40 years ago, in his book “Human Color Vision,” Boynton wrote “The chromatic code of the visual nervous system is incomplete and difficult to interpret;” however, a series of recent discoveries are providing the missing puzzle pieces needed to complete a picture of the diversity of ganglion cell types involved in primate color vision and their varied functions. Boynton proposed a model that, in its simplest form, has just two color channels, red-green (RG) comparing L vs. M cones and blue-yellow (BY) comparing S-cones to the other two types. Neurobiological explanations of color vision have focused on the two ganglion cell types that most closely correspond to the channels Boynton described, small bistratified for BY and midget ganglion cells with L vs. M opponency for RG. However, in contrast to this simple idea, recent evidence suggests that there are many ganglion cell types and subtypes in the primate retina that carry color information. These have appeared at vastly different times over the history of the evolution of vertebrates, they project to several different places in the brain and serve a variety purposes. Many appeared before mammals evolved; including color coded ganglion cells involved in the modulation of sleep and mood, guidance of movements, detection and object segmentation. In contrast, based on recent results we suggest that four specific types of chromatically coded ganglion cells evolved exclusively in primates for the uniquely anthropoid function of assigning blue, yellow, red and green colors to objects for use in identification and classification.