The first thing you might notice about Delacour’s langur is its color. It has a jet black torso, limbs, and head, with a hairy white ass sandwiched in the middle. (These monkeys— Trachypithecus delacouri if you want to get technical—literally look like Oreos.) But that’s what adults look like. Babies are another story: they are orange. https://www.lablogueuse.fr
This is their distinct “native coat”, which fades after a few months. Babies of dozens of other primate species also have fur that is a different color than adults. “One of the big questions has always been why – why would they have separate coats? asks Ted Stankowich, evolutionary ecologist and director of the Mammal Lab at California State University Long Beach.
Primatologists have thrown around a lot of ideas, depending on the species. It may be an environmental adaptation. Or a tried-and-true ploy to get the attention of nearby adults. Now, writing in the American Journal of Biological Anthropology , Stankowich’s team think they’ve got it figured out, and the answer is a bit grisly: the strange coats can protect babies from infanticide.
In primates, new mothers care for their babies in tight social groups, or troops. Langurs, for example, live in groups of 20 to 50 with several (often related) females, their offspring and a male. Every two or three years, an intruding male from another troop may oust the dominant male and take over. These intruders want to mate with the females, and they bring new genes with them. But if they happen while a woman is breastfeeding another man’s baby, they can cause problems. “Adult males who come in and take over a troop will kill the infant in order to bring the mothers back into estrus sooner,” Stankowich explains.
The team analyzed data on infant and adult coats, behavior and biology for 286 primate species, and they found a strong correlation between species with distinct infant coats and the occurrence of infanticide. The team’s hypothesis is that hair color is an indirect form of protection: babies with distinct coats elicit more care from their mothers. When infants receive more attention and care, they grow faster. This means they are vulnerable for less time. “Infanticide can happen at any time,” says Stankowich. “And the shorter the interval during which these infants are sensitive and small, the better it is for