Researchers from the University of California were also struck by the enormous diversity of New World monkey faces, and studied 129 of them belonging to adult males of different species. The faces they studied evolved over at least 24 million years, they report. Like big brother the further evolved ‘human being’ all other primates are visually oriented, and facial expressions provides a lot of information. But how and why did faces and facial features evolve into so many different appearances?
Their findings led to the idea that when species live in larger groups, their faces evolve into quite bare (more simple, more plain) faces. This could increase the ability to communicate using facial expressions. Because a plain face could allow better distinguishing of the different features of these expressions, without distraction by the colours for instance. Nevertheless, it came as a surprise for the researchers as they initially thought and expected the opposite according to Sharlene Santana, one of the authors. She said: “You might expect that in larger groups, faces would vary more and have more complex parts that would allow one individual to identify any member of that group. That is not what we found. Species that live in larger groups live in closer proximity to one another and tend to use facial expressions more than species in smaller groups that are more spread out. Being in closer proximity puts a stronger pressure on using facial expressions.” (ScienceDaily)
Living in larger groups also means that a highly developed social structure exists, so if species are highly social, facial expressions are more important than highly complex patterns on their face. Which is what the researchers found in species living in smaller groups and living together with high numbers of similar species. In these species more complex patterns of facial colour have evolved.
In addition to these findings the scientists found that ecological factors influenced the evolution of facial pigmentation and hair length. Species living closer to the equator have darker skin and hair around their eyes. Furthermore, facial regions around the nose and mouth get darker when species live in humid environments and denser forests, while facial hair gets longer as species live farther from the equator and the climate gets colder, which may be related to regulating body temperature. (ScienceDaily)
The scientists, Santana, Alfaro and Alfaro, envisage that computer facial-recognition software may become part of their tools to help quantify the faces in a more sophisticated way in the future. And even more interestingly, they plan to study the faces of carnivores, including big cats.
(Sources: Proceedings of the Royal Society B, 11.01.2012; ScienceDaily, 11.01.2012)