text: Monkeys' faces evolved to avoid crossbreeding 
   
   Researchers used human face recognition techniques to identify and compare guenons' features 
   
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   Guenon monkeys' colourful and varied faces have evolved as a way to avoid crossbreeding, scientists have found. 
   
   Many different species of guenons live side-by-side meaning mating with other species, which could lead to infertile offspring, is a possibility. 
   
   The researchers used human facial recognition technology to identify primate features from photographs. 
   
   They found that guenons' looks have evolved to become more distinctive from their relatives living close by. 
   
   The findings are reported in the journal Nature Communications and researchers say they are the best evidence to date of visual signs acting as a barrier to breeding across species. 
   
   Guenons - Cercopithecini - are a group of more than 25 species of monkeys which originated in the forests of Central and West Africa. 
   
   Multiple species often travel, feed and sleep together increasing the likelihood of mating with each other. 
   
   Guenons have markings which include differently coloured eyebrow patches, ear tufts, nose spots and mouth patches. 
   
   In the 1980s, Oxford zoologist Jonathan Kingdon suggested the guenons' variety of facial appearances was due to their need to identify their own species and avoid mating with others. But he failed to find firm evidence for his theory. 
   
   The researchers from New York University, US, and Exeter University, UK, wanted to test Mr Kingdon's explanation by using modern identification methods. 
   
   They spent 18 months photographing 22 species of guenons in zoos in the US and UK and in a wildlife sanctuary in Nigeria. 
   
   Primates' features were distinguished and compared with other species using a computer programme developed for human face recognition (known as the eigenface technique). It is the first time such techniques have been applied to non-human faces. 
   
   Continue reading the main story “ Start Quote How you end up looking is a function of how those around you look.” End Quote James Higham New York University 
   
   The results showed the face patterns of guenon species have evolved to become more visually distinctive from other guenons, especially those they come into contact with and therefore are at risk of crossbreeding with. 
   
   Dr James Higham, senior author, said: "Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species. 
   
   "A key question is what mechanisms keep closely related species that overlap geographically from interbreeding, so that they are maintained as separate species. 
   
   "Our findings offer evidence for the use of visual signals to help ensure species recognition: species may evolve to look distinct specifically from the other species they are at risk of interbreeding with," Dr Higham said. 
   
   "In other words, how you end up looking is a function of how those around you look. With the primates we studied, this has a purpose: to strengthen reproductive isolation between populations." 
   
   Scientists have previously shown examples of species being differentiated (called character displacement) by acoustic and electric signals but the authors believe their research is the best example of visual variety across a broad group. 
   
   "These results strongly suggest that the extraordinary appearance of these monkeys has been due to selection for visual signals that discourage hybridisation," lead author William Allen said. 
   
   "This is perhaps the strongest evidence to date for a role for visual signals in the key evolutionary processes by which species are formed and maintained, and it is particularly exciting that we have found it in part of our own lineage." 
   
   The team is now carrying out more research to find out whether guenons are more distinctive from those species they now live beside or those they were living with at the time their species emerged. 
   
   Join BBC Nature on Facebook and Twitter @BBCNature. ||||| With bushy beards and funky blue, yellow or brown faces, guenon monkeys have some of the most colorful and quirky faces of all primates. A close study of more than 20 guenon monkey species reveals these sociable animals may rely on their distinctive patterns to prevent interbreeding. 
   
   "Animals use coloration and patterning for a whole host of different reasons, and we think guenons are using their patterns to recognize different species," said study lead author William Allen, of the University of Hull in the United Kingdom. 
   
   Guenon monkeys live in the forests of Central and West Africa, eating mostly fruits, insects and leaves. Sometimes called cheek pouch monkeys, most guenons are the size of cats and dogs, and they forage in large groups of two or more different species. Each species has unique chirps, sneezes and whistles, but the monkeys learn other species' warning calls like a foreign language, providing protection for all groups. [Photos: Adorable Guenon Monkey Faces] 
   
   There are as many as 35 guenon monkey species, and spending so much time with other friendly monkeys means running the risk of interbreeding. If guenons mate across species, their offspring might be infertile or less healthy, similar to when donkeys and horses breed, Allen said. Guenons can interbreed in zoos, but rarely do so in the wild. 
   
   For decades, many researchers have thought that guenons' unusual fur and facial features were meant to send "I'm different" signals to other monkeys. However, while there are many examples of wild creatures signaling with skin patterns and colors, such as the bright red patch on the abdomens of black widow spiders, scientists have had little success actually proving these patterns are a means of species-wide communication in the guenons, Allen said. 
   
   To show that the these monkeys speak to each other with their stylish fur, Allen relied on facial recognition software. He photographed more than 150 guenons, both wild monkeys living in Africa and individuals in zoos and preserves. Then, he analyzed how facial patterns differed among monkeys within a guenon species, as well as how the patterns differed among species. Allen said he thinks the software algorithm recognizes facial features in a manner similar to how the guenon monkeys do it. 
   
   It turns out the facial patterns are remarkably similar within a guenon monkey species. That is, all guenon monkeys are alike if they are the same species. But each different species has developed its own dramatic flair, whether it's a furry white nose, a ruffly black mohawk or pursed pink lips. 
   
   The new findings were published today (June 26) in the journal Nature Communications. 
   
   The researchers suspect that the close living style of the guenon species, combined with repeated expansion and contraction of the monkeys' forest habitat, drove the development of their incredible facial diversity. For example, isolated groups living in far-flung forests were squeezed together when their habitat shrunk, forcing them to live with different species, Allen said. 
   
   "Where species came into contact with each other, they developed visual signals so they didn't get confused with each other," he said. 
   
   Researchers studying primates in South America have discovered a similar pattern, with more-complex facial features among primates who need to quickly recognize members of their own species. 
   
   Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on Live Science.
target: – Guenon monkeys are renowned for their colorful, distinctive faces, which vary from species to species. The reason? It's all part of a strategy to help the monkeys identify their own species and avoid crossbreeding with others, new research finds. Guenon monkeys, sometimes known as cheek pouch monkeys, are a group of perhaps 30 species that tend to live side by side. To prevent mating across species and possible unhealthy offspring, researchers think each species developed varying features—like mohawks, pursed lips, or white noses—as markers, LiveScience reports. US and UK researchers spent a year and a half snapping photos of 22 guenon species, then compared their features using a human-face-recognition program—the first time such a thing has been used on non-humans. What they found: The monkeys' faces evolved to look different from guenons in other species, especially those with whom they were in close contact, reports the BBC. "In other words, how you end up looking is a function of how those around you look," a researcher says.