Fig. 2

The red faces on these Japanese macaques (Macaca fuscata), also known as the Snow Monkey, may provide information to potential mates about mate quality. In the rhesus macaque (Macaca mulatta), females prefer the red version of males’ faces (Waitt et al. 2003). M. fuscata is a terrestrial Old World monkey species native to Japan, shown here relaxing in naturally heated volcanic hot springs. Photo courtesy of Wikipedia