Primates are noted for their varied and complex pelage and bare skin coloration but the significance of this diverse coloration remains opaque. Using new updated information, novel scoring of coat and skin coloration, and controlling for shared ancestry, we reexamined and extended findings from previous studies across the whole order and the five major clades within it. Across primates, we found (i) direct and indirect evidence for pelage coloration being driven by protective coloration strategies including background matching, countershading, disruptive coloration, and aposematism, (ii) diurnal primates being more colorful, and (iii) the possibility that pelage color diversity is negatively associated with female trichromatic vision; while (iv) reaffirming avoidance of hybridization driving head coloration in males, (v) darker species living in warm, humid conditions (Gloger’s rule), and (vi) advertising to multiple mating partners favoring red genitalia in females. Nonetheless, the importance of these drivers varies greatly across clades. In strepsirrhines and cercopithecoids, countershading is important; greater color diversity may be important for conspecific signaling in more diurnal and social strepsirrhines; lack of female color vision may be associated with colorful strepsirrhines and platyrrhines; whereas cercopithecoids obey Gloger’s rule. Haplorrhines show background matching, aposematism, character displacement, and red female genitalia where several mating partners are available. Our findings emphasize several evolutionary drivers of coloration in this extraordinarily colorful order. Throughout, we used coarse but rigorous measures of coloration, and our ability to replicate findings from earlier studies opens up opportunities for classifying coloration of large numbers of species at a macroevolutionary scale.

Objectives: Neonates of several primate species are born with very different pelage coloration from their parents but then assume adult coat color within weeks or months of birth. We set out to test the three conventional functional hypotheses for this distinctive transient natal coat coloration in primates (infanticide, allomothering, and confusion of paternity) as well as solicitation of maternal care, and across all neonate primates, background matching, and Gloger's rule (dark coats being associated with humid environments). Materials and Methods:To examine the functional significance of neonate pelage coloration, we employed five different measures of distinctive coat coloration, new updated information on primate life histories, and a complete primate phylogeny of 286 species to control for shared ancestry.Results: Across primates, we found a strong association between distinctive natal coats and the prevalence of infanticide but no support for allomothering or confusing paternity. We also found that species in which young have distinct natal coats have relatively shorter interbirth intervals, as well as a tendency to be weaned earlier which is unrelated to allomothering. Darker primate natal coats (whether distinctive or not) are not found in shadier, warmer, or wetter habitats.Discussion: While distinct natal coats in primates are generally found in infanticidal species, we argue on logical grounds that this is not an advertisement to incoming males but instead neonate coloration solicits greater maternal care. This enables infants to pass through this infanticide-induced mortality-prone infant phase more rapidly. Conspicuous neonate coats in comparison to adults appear to act as a supernormal stimulus for mothers to hasten post-natal development of their offspring.