Primate Faces and Facial Expressions - )

Social Research, Spring, 2000 by Signe Preuschoft

Many non-human primates have peculiar hair styles, mustaches, beards, whiskers, or tufts, but sexual dimorphism with respect to facial hair is usually less conspicuous than in humans, though differences in the skin color of males and females may be pronounced. In contrast to humans, some non-human primate species possess blue facial skin, or even multi-colored skin ornaments (e.g., the male mandrill, Papio mandrillus sphinx). The pupils of all primates are round, like ours. Almost all primates have brown or amber irises, but only very few species have visible, white eyeballs (e.g., pigtailed macaques, Macaca nemestrina). Like humans, non-human primates often have visually emphasized eyebrows or lips. There is a trend towards bald faces, especially around the mouth. A few species have protruding noses, but the shape of noses, eyes, jaws and ears varies widely among species.

A simple yet scientifically sound means to distinguish primates is by their noses. The strepsirhines are characterized by a rhinarium, a moist patch of mucous skin on the tip of the pointed nose, extending down to the upper lip, which is used to smell and taste. Since they share the rhinarium with other orders of mammals, for instance the carnivores, the strepsirhines are considered the most ancestral group of primates.

Take a look at a slender loris (Loris tardigradus), for instance. A slender loris is a small, tailless creature with a body shaped like a banana and roughly a banana's size, too. It has a dense, velvety coat of brown-beige fur. On tropical nights, it noiselessly stalks insects in bushes and low trees, moving slowly and carefully on skinny limbs that end in moist hands and feet. The lofts' head is relatively large, with mobile ears, not too big, placed high on the sides of the head, slightly above the temples (see Figure 1). Sitting side by side in the front of the face, the huge eyes dominate the loris' face. The eyes sit side by side on the front of the face. They are perfectly round, and no eyelids are visible. Like cats and other nocturnal mammals, the loris has a layer of special cells, the tapetum lucidum, embedded in its eyes. The tapetum reflects light, and thus enables the loris to make the most of even small amounts of light for better vision. If you shine a torch on a loris in the night you will see two enormous, lucent discs suggestive of a much bigger animal. Each eye is surrounded by a ring of dark brown fur that elongates and peaks just above each eye. Seeing a loris face-to-face one hardly even notices its mouth. Quite conspicuous, however, is the pinkish snub nose, protruding forward and ending in a pea-sized knob covered by the rhinarium. To the unintentionally anthropocentric beholder the loris looks cute and perpetually surprised, as if its eyes were widened and its eyebrows raised in curious bewilderment. Loris specialists, however, will assure you that lorises do have other facial expressions in their repetoire.

[Figure 1 ILLUSTRATION OMITTED]

The next group of primates are the haplorhines--those with dry noses, like ourselves. These are further divided into those with wide noses, the platyrrhines, and those with narrow noses, the catarrhines. The platyrrhines are the New World monkeys of South and Central America, the catarrhines are the Old World monkeys and apes in Africa and Asia. The primates of the New World and the Old World seem to have evolved in parallel, originating from a little known common ancestor about 30 million years ago.