A new research has revealed that Old World monkeys have unique facial features to avoid interbreeding. Monkey populations and species living in close proximity to each other look so different to ensure reproductive isolation between populations.

Findings of the study have been published in the journal Nature Communications. "Evolution produces adaptations that help animals thrive in a particular environment, and over time these adaptations lead to the evolution of new species", said study author James Higham, an assistant professor in New York University's Department of Anthropology.

Researchers from NYU and Exeter University, in the United Kingdom, conducted the study to determine what mechanisms keep closely related species that overlap geographically away from inter-breeding.

After taking pictures and analyzing the facial features of 22 types of guenons, or Cercopithecini, the researchers reached at the conclusion that the extraordinary appearance of these monkeys helped them prevent hybridization. Guenons are the first species that evolved in the forests of Central and West Africa.

Also, the researchers showed that each species' markings and features became more distinct over time. Facial features included colorful eyebrow patches, ear tufts, various face markings, nose spots, mouth patches, and more.

The study has provided the strongest evidence about a role played by visual signals for many monkey species to avoid interbreeding with closely related and geographically proximate species, said lead author William Allen.

The study suggested significant evolution in appearance for old world monkeys among sympatric species that often travel, feed and sleep side-by-side.

William Allen and James Higham of NYU and Martin Stevens of the University of Exeter examined 22 unique faces of guenons in their study.