It is in many species a deterioration which accompanies senility. Judging from the uses of graying among the primate species just discussed and its occurrence and location, we can conclude that both of these forces have been at work. Chimps offer an interesting medium to study the evolution of status graying. Many primates have contrastingly colored snouts, beards, and cheek whiskers. Among some they are white.
Some chimps have white hair on the snout from birth and others gray around the mouth with age.
Though we all pretty much know qualitatively the age sequence of graying and the patterns in which it occurs, let's map a little more precisely the various parameters of the graying process. Humans do not gray randomly, but in a specific pattern. These can occur singly or in combination. People possessing all of these have an alternating variegated swirl of contrasting lines. Like gorillas, chimps, and baboons, we have a characteristic graying pattern.