How Evolution Made the Monkey Face

DATA The Matrix HOWHOW EVOLUTIONEVOLUTION MMAADEDE TTHHEE MONKEYMONKEY FFAACECE The complexity, or lack thereof, on a simian’s face reveals a great deal about its society. curious thing happens to white-faced capuchin monkeys Santana found that the complexity of a species’ facial color when they anoint their bodies with mud and plant mat- patterns is tightly linked to certain social systems. Species that ter, a natural insect repellent: With their heads and faces live in larger groups tend to have plainer faces than those living in Aslathered in goop, these highly social primates lose their ability to smaller groups. Primates in large social groups most likely benefit recognize each other. Previously friendly monkeys can become from plain faces that allow for a greater range of expressions, she fighting foes. This abrupt change in behavior hints at the impor- explains. But among primates in smaller groups (and those that tance of facial expressions for recognition, University of Wash- live near many different species, regardless of group size), more ington evolutionary biologist Sharlene Santana says, and could complex patterning makes it easier to recognize members of their help to explain why primate faces are so wildly divergent: Some own species, so they can focus their mating efforts and territorial species, like white-faced capuchins, have monotone hair and skin disputes where it counts. color; others, like the northern owl monkey, sport a dramatic mix The connection between group size and facial evolution tells us of fur and flesh tones. something about our own ancient history too, since human faces Biologists have long seen primates’ facial expressions during are about as plain as it gets. “We can predict that the ancestors social interactions as clues that factors like group size drove the of humans were living in large groups, where facial expressions stark differences in their facial evolution. But there was little direct were really important,” Santana says. She is currently investigat- evidence to support the theories, so Santana decided to study a ing whether her results hold up among the Old World primates of large number of monkey species, in a wide variety of social group Africa and Asia, a group that includes monkeys like baboons and sizes and environments, to see how their faces had evolved. mandrills and apes such as orangutans and chimps. JENNIFER ABBASI CacaJao calVUS / LeontopithecUS rosalia / Lagothrix cana / Geoffroy’S SagUINUS imperator / CebUS nigritUS / AotUS triVirgatUS / Ateles belZebUTH / White- SYSTEM/FACIAL PATTERN Bald-headed Uakari Golden lion tamarin woolly monkey Emperor tamarin Black-horned capUchin Northern owl monkey bellied spider monkey COMPLEXITY SCORE Researchers counted the number of unique skin and hair colors to score facial pattern complexity among 129 species of New World monkeys, which OOSMALEN reside in Central and South R AN America. V . M Facial pattern complexity Complexity score: 1 (Very low) Complexity score: 2 (Low) Complexity score: 2 (Low) Complexity score: 2 (Low) Complexity score: 4 (Medium) Complexity score: 5 (High) Complexity score: 6 (Very high) ARC G. ARC scores ranged from 1 to 6. M Don’t let the bright-red vis- For the golden lion tamarin, Simple black faces give ER; These monkeys would have This black- or brown-furred The northern owl monkey, The white-bellied spider F 1 = Very low age fool you: With only one Brazil is chilly enough to these furry monkeys a blank INDEN PICTURES very simple gray faces if it species gets its common a wide-eyed, nocturnal monkey has one of the M CHA 2 = Low facial color, this monkey is warrant a luxurious red fur canvas for communicat- S weren’t for their striking name from two characteris- critter, has particularly most complex faces of New ORD/ F 3 = Low/medium as plain as they come. The coat. The species makes its ing facial expressions, a X moustaches. The primates tic tufts of hair on its crown, complex facial coloration. World species. Yet it lives O 4 = Medium species lives in large groups, home in forests 1,500 miles necessity in large groups of are a bit of a mystery. They but a ring of white frames its The animals live in pairs in large groups of about 20, ORBIS; KEVIN ORBIS; KEVIN 5 = High averaging 20 members but south of the equator, provid- around 18 members. The C live in medium-size groups otherwise dark face. These with their offspring, and where plain faces would ER; PETER 6 = Very high swelling to as many as 100. ing evidence for the “hair overall dark coloring of the F of around five, but research- monkeys live in medium-size occasionally a family will be more advantageous for The uakari’s monotone face rule.” This theory predicts species is also an example CHA ers have called them “poker groups of around nine, and also include a young adult. nonverbal communication. S Low complexity was and lack of facial hair could that longer, thicker hair will of Gloger’s rule, which pre- ER; faced” for their lack of facial females usually outnumber For animals living in such What gives? This species, F common in monkeys living make it easy for others to develop in cold climates. dicts that mammals in warm, INDEN PICTURES/ expression. Males, females, males. Known for their tool small groups, it is especially which spans northwestern CHA M in large groups, while those read its expressions. Blood The primates have low facial forested habitats with low S and juveniles sport the fan- use and prehensile tails, important to accurately South America, shares its ER; F living in small groups or flow through a large number pattern complexity and live light and high humidity will ARENT/ ciful facial hair, and nobody they can communicate identify other members habitat with three closely M CHA near other types of of facial capillaries gives the in medium-size groups, but have dark skin and hair. This S knows why. The display via body language, facial of their species. How else related species, a situation face its scarlet hue, which the takeaway here is that provides camouflage from could be a rare example of expressions, and sometimes to find a viable mate or monkeys tended to have HOMAS that gives an advantage to T T: KEVIN KEVIN T: potential mates may regard climate can play a major role predators and resistance T: the same sexual selection with a high-pitched scream fend off a territorial en- monkey species that can F more complex color F E patterns. as a signal of good health. in facial appearance. against certain bacteria. L trait at work in both sexes. followed by a big hug. croachment? tell each other apart. FROM FROM FROM LE FROM 18 19 DISCOVER 03.2013.

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