From the adorably mustachioed emperor tamarin (#11, above) to the demonically bald uakari  (#1), the faces of South America's primates come in all shapes and colors. Some of these differences give the animals adaptive advantages—brown fur is better than white for camouflage, for instance—but many monkeys sport very complicated, multicolored patterns. Using facial recognition software, researchers mapped out the faces of 129 species of New World monkeys and rated them by the complexity of their colors. Then they looked for patterns in the primates' lifestyles. Monkeys who live in small groups or alone tended to have more complex faces  (indicated by red labels) than those who live in large groups, who tended to have simpler faces (blue lines), the researchers hypothesize today in the Proceedings of the Royal Society B. The reason might be that monkeys with many colors, such as the spider monkey (#3), are more conspicuous to one another, allowing one individual to quickly recognize another from the same species, since such interactions may be few and far between. The next line of research: Can they quickly recognize those bright red or blue butts?
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