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Human Origins 201: Human teeth [1]
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Date: 2025-03-15
Teeth provide us with important information about the past, both about the kinds of foods which were eaten and about human evolution. In her book Written in Bone: Hidden Stories in What We Leave Behind, British forensic anthropologist Sue Black writes:
“We form the type of teeth we are going to need to manage our diet. Canines are essential equipment for carnivores but surplus to requirement for herbivores. Both need incisors and molars, but the molars are of a different type. The committed carnivore will have carnassial, or slicing, molars that act like scissors to snip off the pieces of meat it consumes, while the herbivore has grinding molars. As humans are omnivores, and eat a bit of everything, we have incisors to nibble and pinch, canines to pierce and molars to grind.”
Humans are, of course, closely related to apes, particularly chimpanzees. Humans and chimpanzees share a common ancient ancestor, so one starting point is looking at the clues teeth provide us about human evolution is to compare modern humans and chimpanzees. Humans have the same dental configuration as apes: 8 incisors, 4 canines, 8 premolars, and 12 molars. However, humans have smaller teeth than chimpanzees. In his book Catching Fire: How Cooking Made Us Human, Richard Wrangham writes:
“Human chewing teeth, or molars, also are small—the smallest of any primate species in relation to body size.”
In his book The Origins of Language: A Slim Guide, James Hurford reports:
“Chimpanzees have huge teeth compared to ours. Human teeth have shrunk in size since the split with chimpanzees. It is very plausible to connect this change with the cultural practices of cooking and grinding food. Cooked or ground food needs less chewing. The reduction in teeth size, then, probably happened quite late and fast in our evolution, starting with the use of fire, probably by Homo erectus. Interestingly the trend toward smaller teeth has continued until modern times; this may be physical evolution still catching up with cultural evolution.”
Humans also have smaller chewing muscles. Among other primates, such as chimpanzees, 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.”
Richard Wrangham explains:
“The cause of our weak jaws is a human-specific mutation in a gene responsible for producing the muscle protein myosin. Sometime around two and a half million years ago this gene, called MYH16, is thought to have spread throughout our ancestors and left our lineage with muscles that haven subsequently been uniquely weak. Our small weak jaw muscles are not adapted for chewing tough raw food, but they work well for soft, cooked food.”
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. In his chapter on the continuation of human evolution in The Story of Us, John Hawks writes:
“Ten thousand years ago, for example, people’s teeth averaged more than 10 percent larger in Europe, Asia and North Africa than today. When our ancestors started to eat softer cooked foods that required less chewing, their teeth and jaws shrank, bit by bit, each generation.”
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
Note: The designation 201 indicates a revision of an earlier essay.
Human Origins 201: The human hand
Human Origins: Fossil Evidence
Human Origins: The impact of the horse
Human Origins: The Large Brain
Human Origins: Religion and the brain
Human Origins: Alfred Russel Wallace and Charles Darwin
Human Origins: Lamarckian Evolution
Human Origins: Homo habilis
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