'Monkey Facebook': The Message Inherent in Diverse Faces of Social Primates

The more social a species, the more complex their facial patterns.

By Ajit Jha on November 20, 2013 8:40 AM EST

Monkey Facebook
Color patterns on primate faces help individual monkeys tell their own species apart from other, closely related species, and also help individuals communicate with members of their own species. (Photo: University of California - Los)

While all primates look sort of the same, some are more alike than others. Yet, as far as the facial colors of primates go, a clear and distinct pattern can be found. Faces of some primates contain a true diversity in colors including red, orange, blue, and black. Some have faces that are white mixed with colors in different proportions, while other primate faces are simply plain.

UCLA biologists are currently studying the evolution of primate faces in order to more fully understand why such a diversity in color exists. Last year, a team from UCLA studied the evolution of 129 primate faces among Central and South American species. Their latest report is on the evolution of faces of 139 Old World primates from Asia and Africa.

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According to their findings, the complexity of facial patterns of Old World primates is proportional to their social nature. In other words, the more social a species is, the more complex their facial pattern gets. The finginds imply that species with smaller group sizes have simpler faces with fewer colors. Having more diversity in larger groups is logical: after all, it should aid in identifying individuals within a big crowd.    

The UCLA study adopted a comparative approach to investigate the evolution of facial traits and their correlations with ecological, geographi,c and social pressures across four catarrhine (Old World monkeys and apes) radiations. The researchers found that facial color patterns have an intimate link with social factors. In other words, the species that are more gregarious and sympatric have more evolved colors in their faces. Ecological factors determine facial pigmentation, so the species inhabiting dark, dense, and humid tropical forests in Africa have tended to evolve to have darker faces. In other words, the two most prominent factors that explain the diversity of faces in primates, apes or mammals are gregariousness and ecology.     

According to Michael Alfaro, associate professor of ecology and evolutionary biology in the UCLA College of Letters and Science, and senior author of the study, while humans are crazy for Facebook, primates have been using faces to differentiate friends from competitors for over 50 million years. In addition, "social pressures have guided the evolution of the enormous diversity of faces we see across the group today," said Alfaro.

Emphasizing upon the facial diversity, Alforo said, "Faces are really important to how monkeys and apes can tell one another apart." The color patterns are important for two reasons, according to Alforo: identifying a member of a species apart from closely related species as well as for social communication within the species. 

"Faces are really important to how monkeys and apes can tell one another apart," he said. "We think the color patterns have to do both with the importance of telling individuals of your own species apart from closely related species and for social communication among members of the same species."

Jessica Lynch Alfaro, co-author and an adjunct assistant professor in the UCLA Department of Anthropology and UCLA's Institute for Society and Genetics said most apes and primates are social. On one end of the spectrum are species like the mandrills, with highly gregarious instincts. They are found in groups of up to 800 members. On the other end of the spectrum, loner species like orangutans live, travel, and sleep alone, while their females have only their young to accompany them, said Lynch Alfaro.

In addition, there are "fission-fusion societies" of chimpanzees, that fall somewhere in between. These chimps spend most of their time in small groups, but occasionally form large communities. Some apes like hamadryas baboons have evolved social tiers to include troops, bands, clans, and harems, according to Lynch Alfaro. 

The research published in the journal Nature Communications, Nov. 11 was federally funded by the National Science Foundation and supported through a postdoctoral fellowship from the UCLA Institute for Society and Genetics. 

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