In an effort to avoid interbreeding, Old World monkeys have gone through a stunning evolution in facial appearance. This change is to help avoid interbreeding with species that are within the same geographical range and that are closely related, according to researchers from New York University and the University of Exeter.

The latest research offers the best evidence so far regarding the role of visual cues as barriers to breeding across species.

James Higham, the study’s senior author, assistant professor in NYU’s Department of Anthropology, said in a statement, “Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species.” He continued, “A key question is what mechanisms keep closely related species that overlap geographically from inter-breeding, so that they are maintained as separate species.”

Higham further explains, “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 inter-breeding with. 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.”

According to nature.com, Old World monkeys are primarily found in Africa and Asia, living in habitats ranging from deserts to snowy mountains to cities.