Diet is a fundamental aspect of an organism’s ecology. The food an organism consumes provides its body with nutrients to function and maintain basic life. Diet is also indicative of the environment in which an organism lives. In today’s western society, we are often easily able to access specialty foods from all over the world. Living in the diverse community of Boulder, CO, I could enjoy Ethiopian, Italian, Tibetan, Vietnamese, Chinese or German food, all within a short distance from my home. However, our early hominin ancestors did not have the luxury of such variety. As a result, the changes researchers have observed in hominin diet have been hailed as key milestones in human evolution.
When observing early hominin diets, paleoanthropologists generally create four principal groups of interest: The Miocene-Pliocene probable hominins (about 7-4 MYA), the Pliocene-Pleistocene ‘gracile’ australopiths (about 4 MYA), the Pliocene-Pleistocene ‘robust’ australopiths (about 2.5 MYA) and the earliest members of Homo (about 2.5 MYA)(18).
Prior to the introduction of new methods in the last several years, theories regarding the diets of these groups were predominately based on the overall shape, size, and structure of teeth, resulting in paleoanthropologist’s observations being limited to only one lens: morphology. Observations of the recovered teeth of Miocene-Pliocene probable hominins like Sahelanthropus tchadensis, Orrorin turgenensis, and Ardipithecus ramidus, indicated smaller and thinly enameled molars similar to extant chimpanzees. As a result, paleoanthropologists suggested a diet primarily composed of fleshy fruits and soft, young leaves for the Miocene-Pliocene probable hominins.
The later gracile and robust australopiths, however, exhibited a craniodental morphology with thickly enameled, large, flat cheek teeth, combined with heavily built crania and mandibles relative to extant apes (6). This led many researchers to believe that there was a shift from the previously softer diet to one dominated by hard and abrasive foods like brittle nuts and seeds, or underground storage organs (USO). The more robust australopiths (Paranthropus) showed even larger teeth with massive chewing muscles. This led to the notion that they consumed even harder foods and/or relied more heavily on hard foods than their gracile counterparts (1).
When observing the earliest members of our own genus, Homo, evidence showed smaller cheek teeth, thinner enamel and a higher occlusal relief compared to their australopith predecessors. Additionally, evidence of tool use has been associated with Homo. This steered many paleoanthropologists to believe that Homo was able to process a broader range of foods, like meat and USO’s and that the morphological differences were caused by selective pressure resulting from extraoral processing (11&7). While all of these observations hold scientific truth, they are limited in their accuracy due to the evidence relying only on morphology.
Thankfully, over the last couple of decades, our understanding of early hominin diet has advanced substantially as a result of new methods, dental microwear, and stable isotopic analyses, as well as the discovery of new fossil species and additional specimens. Improved paleoclimate and paleoenvironment reconstructions have also contributed to a broader understanding of hominins. These advancements have allowed researchers to better define and alter previous theories arriving at a more comprehensive understanding of early hominin diet.
Have you ever eaten popcorn and accidentally bitten into an un-popped kernel? If you have, you’ve likely experienced a form of dental microwear. Dental microwear are pits and scratches that form on a tooth’s surface as the direct result of its use. When you bite down on an un-popped kernel or any hard and brittle food, the microwear left behind resembles a pit. If, however, you are trying to shear through a tough food like beef jerky, the microwear patterns will instead show long, parallel striations (20, 6 & 16). Our teeth, like all mammal teeth, tend to show a strong and constant association between microwear patterns and food fracture properties, thus allowing researchers to trace the chewing events of an individual. Unfortunately, microwear is fleeting, since individual features are replaced by new ones as the tooth naturally wears down. This effect is also known as the “last-supper” phenomenon because when paleoanthropologists look at tooth wear in early hominins they are observing the diet in the days or weeks before the death of the individual (18).
The phrase “you are what you eat” can be directly applied to stable isotope analysis. Stable isotopes, which are found within every item that an individual consumes, will be incorporated into the teeth and bones of that consumer. Stable isotopes are atoms whose nuclei all contain the same amount of protons, but different amounts of neurons (8). When observing stable isotopes in hominin paleodietary studies, carbon isotopes are typically chosen.
This is due to carbon isotopes showing the type of photosynthetic pathways for a use, relative to proportions of carbon- Carbon 3 (C3) or carbon 4 (C4) (14&18). C4 indicates tropical grasses while C3 indicates trees, bushes, and forbs. Now, you might wonder how we can reconstruct the diet of early hominins when we are only looking at flora. Well, just as the phrase “you are what you eat” suggests, carnivores will show different proportions of carbon depending on the proportions that their prey consumed. Simply put, biological anthropologists can determine what species eat by examining each trophic level on the food chain.
Both microwear and stable carbon isotope studies have challenged many long-held assumptions regarding early hominin diets. Previous assumptions that the craniodental morphology of early hominins evolved as the result of their increased consumption of hard, brittle foods due to the expanding of open savanna landscapes is either incorrect or just too simplistic. For example, none of the teeth of gracile or robust australopiths show the heavily pitted surfaces that would indicate their being hard-object feeders, as originally expected given their morphology (14). It has been suggested that the distinct differences between microwear and morphology relate to ‘fall-back’ foods, meaning that australopith dental anatomy evolved to cope with harder more brittle foods consumed when their preferred foods were unavailable within their environment. Additionally, carbon isotopes show that Ar. ramidus, the earliest taxon analyzed to date, had a C3 diet much like that of savanna chimpanzees.
There also seems to be a geographic influence on australopiths diets, with the microwear of eastern African Australopithecus and Paranthropus being less complex than that of their South African cousins. Also, within species, like Paranthropus, differences in carbon isotope compositions can be seen (1). For example, P. robustus has been noted to have consumed more than 50% C3 foods, but also substantial quantities of C4 foods. P. boisei, however, had a diet of about 75 to 80% C4 plants, which is similar to grass-eating warthogs, and hippos (18). This variation may possibly indicate that a specialized morphological complex can have more than one function and reflect more than one type of diet.
So, as you flip through your magazine in the waiting room of your dentist, learning about how to eat like a caveman, just remember the impact your teeth could have on enlightening our future hominin lineage. Remember readers: brush, floss, and mouthwash your pearly whites, for your teeth could be the future of hominin history!