Humans have the same dental configuration as apes: 8 incisors, 4 canines, 8 premolars, and 12 molars. However, humans have smaller teeth and smaller chewing muscles than other primates. Among other primates,the larger muscles for chewing are attached to the top of the skull and create a bony ridge. Among humans, the smaller chewing muscles means that the top of the skull is smooth and there are not large muscles running from the jaw to the top of the skull. In his book The Accidental Species: Misunderstandings of Human Evolution, Henry Gee writes:
“The smallness of human chewing muscles has been linked with a particular genetic mutation found in humans but not other mammals.”
In comparing chimpanzee teeth with human teeth,Jonathan Marks, in his chapter in The Oxford Handbook of Archaeology writes:
“The teeth of human and ape differ principally in the relative sizes of the front and back teeth, the absolute size of the canine teeth (and sexual dimorphism in the size of the tooth), and the thickness of the enamel on the molars.”
The reduction of tooth size and chewing muscle size is related to cooking: cooked food requires less chewing than raw food.
The reduction in the size of the canines is often associated with the loss of sexual dimorphism. Sexual dimorphism means that males are significantly larger than females, often two to three times the size of females.
The study of the teeth of our ancient ancestors also provides some clues to changes in diet and evolution. Microwear analysis, for example, provides some insights into diet. In his chapter in The Story of Us, University of Arkansas paleontologist Peter Ungar explains:
“Microscopic scratches and pits form on teeth as a result of their use. Studies of the microwear patterns in living animals show that species that chew soft and tough foods such as grass, for example, get long, parallel scratches on their teeth; those that crush hard and brittle foods such as nuts get pits. Paleontologists have inferred the diet of extinct human species, including Paranthropus robustus and Paranthropus boisei, based on the microwear textures of fossil teeth.”
Eastern and southern Africa were the homes to Paranthropus between about 2.7 million and 1.7 million years ago. Peter Ungar notes: “None of its species gave rise to us; rather they were evolutionary experiments that walked alongside our own early ancestors.” The diets of Paranthropus robustus and Paranthropus boisei were different: P. robustus had a relatively generalized diet which was dominated by tree and brush products with some tropical grasses or sedges. On the other hand, the diet of P. boisei is narrower and is made up primarily of grasses.
More recent relatives, such as Homo habilis (about 2.5 million years ago) ate a broader range of foods. Homo erectus (about 1.5 million years ago) had a still broader diet. Both of these early Homo species had a varied and flexible diet. Peter Ungar writes:
“Foodprints teach us that early hominin diets varied over time and space and that we most likely evolved to be flexible eaters, driven by ever changing climates, habitats and food availability.”
Peter Ungar also reports:
“Dietary versatility allowed our ancestors to spread across the planet and find something to eat on all of Earth’s myriad biospheric buffets.”
In addition to providing information about ancient diets, teeth can also tell us about human migrations. In her book Ancestral Journeys: The Peopling of Europe from the First Ventures to the Vikings, Jean Manco explains:
“Isotope studies can help us discover how far an ancient person moved in his or her lifetime. The geophysical character of the terrain in which a person grows up leaves a characteristic signal in the chemistry of bones and teeth.”
In an article in American Scientist, Christina Cheung writes:
“In archaeology, the most common method used to determine where people lived and whether they moved during their lifetimes is to look at the strontium isotope ratios in their teeth. Strontium varies from place to place because of differing geologies; this variation is absorbed from the soil into water and plants, passes along the food chain, and goes into human teeth as they form a record of where someone lived in childhood.”
One example of strontium isotope analysis can be seen in the burial commonly called “the Amesbury Archer.” Found near Stonehenge in the UK and buried about 2350 BCE, the isotope tests on his teeth showed that he was not local: he probably came from central Europe, near the Alps. Another example comes from the burials from Denmark at Telleborg, the fortress of the tenth-century king Harald Bluetooth Gormsson. The strontium isotope analysis of 48 burials showed that most of the young men, probably soldiers in his army, came from outside of Denmark, particularly Norway and the Slavic regions.
As a final note, it should be pointed out that human evolution has not ended and thus human teeth and the jaws that hold them will continue to change. This may mean the eventual disappearance of some teeth.
More Human Origins
Human Origins: Domesticating Fire
Human Origins: Menopause
Human Origins: The Mind
Human Origins: Humans as naked apes
Human Origins: Bipedalism
Human Origins: Sex
Human Origins: The Human Hand
Human Origins: The Large Brain