Color vision in New World monkeys: di- and/or trichromaticity?

Research carried out by various investigators has indicated significant differences in color vision perception between Old World and New World monkeys. While the former seem evenly trichromatic, the New World monkeys show color vision polymorphism with at least 6 different phenotypes and an absence of trichromacy amongst the males of the Saimiri and Callithrix genera. We summarize the studies of color vision in New World monkeys, including our own data, showing inconsistencies in the outcomes of these experiments, the interspecific differences and the numerous non-tested species. The results are discussed according to the neurobiological hypothesis of male dichromatism in New World monkeys, to the hypothesis that the major function of color vision in primates is its role as an adaptation to feeding ecology as well as to aspects regarding primates evolution. In conclusion, the available data points to the necessity of further work on this problem including behavioral, electrophysiological and generical approaches-before definitive proofs are possible.