Functional Utility of Trichromatic Colour Vision: What Can Studies with Monkeys Tell Us ?
In most New World primates, there is polymorphism in colour vision. All the males and some of the females are dichromatic (colloquially, colour-blind) and can be one of three phenotypes. The other females are trichromatic; again one of the three phenotypes. Hence within a group of six monkeys, each may see the world in a different way! This colour vision polymorphism present in most New World primates may represent an intermediate step between dichromacy of non-primate mammals and trichromacy of Old World primates. Alternatively the polymorphism may be an adaptation to a specific ecological niche. Whichever is correct, New World primates are of particular interest in this respect, as they provide a model system to study the functional significance of trichromatic colour vision. Theories for the evolution of trichromacy in anthropoids focus on the efficient detection and selection of food, particularly ripe fruits amongst dappled leaves. In this paper I compare the foraging behaviour of di- and trichromatic tamarins both in the wild in Peru and in experimental studies in naturalistic captive conditions. I discuss the findings in relation to the evolution of colour vision polymorphism in New World primates.