You've got the looks

Source:, photo: William Allen/ Nature Communications
Animal species are not all alike. And it’s best if certain species do not interbreed, as the resulting offspring can be infertile. How do fairly similar species living in the same area make sure they only mate with their own?
Madagascar is home to guenon monkeys. Through time, evolution has resulted in 26 species, all of which belong to the genus Cercopithecus. These species are all closely related and they live in close proximity. Because they encounter each other frequently in daily life, they need to ensure that they only mate with those of the same species. As early as the 1980s, a zoologist suspected that the key to their success was the differences in their faces, but he was not able to prove it. The zoologist’s hypothesis has now been dusted off for testing with modern technology.

Various species of guenons were photographed in detail in several areas over the course of 18 months. Specialised computer programs were then used to analyse the photos, in search of differences and similarities between guenon species.

The investigators discovered that the facial differences are quite distinct. The differences are the most pronounced between species that share habitats, thus minimising the chance of interbreeding.