Skull of juvenile Bornean orangutan (top) compared to adult Homo sapiens

Like most great apes, Bornean orangutans (Pongo pygmaeus) have large, sharp, canine teeth. However, these do not grow in until the juvenile orangutan loses its milk teeth, a couple years after weaning (typically between 4-6 years of age).

You can see the evolutionary differences in diet between orangutans and humans, simply by looking at the teeth and shape of the skull. The orangutan has large, broad molars, sharp incisors, and mandibular musculature that has a very broad attachment point on the skull. Bornean orangutans are generally vegetarian, feeding on leaves, berries, and even bark at times. The broad molars are necessary for grinding and breaking down roughage in their diet.

While the human skull given is not the best example, we have smaller molars, weaker mandibular muscles, and fairly dull incisors and canines. Homo sapiens evolved as strict omnivores, but with a very distinct difference from our more simian (and even most of our hominid) ancestors - we cooked our food. Though the roughage early humanity consumed was much tougher than what we eat today (unless you eat roots and nutmeats as a primary diet), cooking foods such as meats and roots broke them down before we ate them. Our skulls required less space for jaws and jaw muscles, and we required less energy to eat than ever before.

Die Säugthiere in Abbildungen nach der Natur. J.C.D. Schreber, 1774.