Food needs to undergo mechanical breakdown in the mouth before it can be swallowed and further digested. This process of mastication, or chewing, is influenced by several factors, including the mechanical properties of food, such as its hardness, texture, and composition, as well as the morphology of the masticatory apparatus—the jaw, teeth, and associated muscles. Understanding how this process has evolved over time in humans and our extinct relatives provides crucial insights into dietary habits and evolutionary history.
Paleoanthropologists have long been interested in reconstructing the diets of our ancestors, as diet plays a significant role in shaping evolutionary outcomes. The types of foods consumed and how they were processed can provide clues about the ecological pressures our ancestors faced. For instance, a nutrient-dense diet that includes high-quality food, particularly animal protein, is believed to have been a driving force behind the evolution of larger brains in hominins. Conversely, a lack of sufficient food resources, especially those rich in essential nutrients, has been implicated in the extinction of several hominin species, including Paranthropus boisei (also known as “Nutcracker Man”), which had a specialized but likely less nutritious diet compared to other species.
Among the many debated topics within paleoanthropology is the dietary habits of South African hominins, particularly species such as Australopithecus africanus and various species of Paranthropus. To better understand how these early human relatives processed their food, researchers have utilized advanced techniques like non-invasive high-resolution computed tomography (CT) scanning and 3D shape analysis of fossilized dental remains. These methods provide detailed insight into how different hominin species chewed, and this can tell us much about their diet and the broader ecological context in which they lived.
One of the most significant findings from recent studies is that the orientation and structure of the tooth roots within the jaw can provide important clues about the chewing dynamics of different hominin species. Through the use of CT scanning and the analysis of nearly 30 hominin first molars from South and East Africa, researchers have made a compelling discovery. Australopithecus africanus, an important species in understanding human evolution, was found to have much wider and more splayed tooth roots than both Paranthropus robustus and Paranthropus boisei. This suggests that A. africanus engaged in more lateral (side-to-side) chewing movements, a sign that it may have consumed foods that required greater grinding or side-to-side jaw motion, such as tough plant material.
In contrast, the two species of Paranthropus—P. robustus and P. boisei—displayed a different pattern of tooth root orientation, characterized by more vertical loads during chewing. These species, known for their large molars and strong jaws, likely consumed a diet that consisted of harder, more fibrous foods that required a more straightforward biting action. This variation in tooth root orientation reflects different strategies for processing food and highlights how diverse the diets of early hominins might have been, even among closely related species.
One particularly intriguing finding in this study was the unusual orientation of the tooth roots in Paranthropus robustus. Unlike any other species analyzed, P. robustus exhibited a distinct “twist” in its tooth roots. This twisting pattern suggests that P. robustus might have used a combination of rotational and back-and-forth movements of the mandible during chewing. This unique jaw movement is supported by other aspects of the P. robustus skull, including the structure of the enamel on their teeth, which indicates a more complex, multidirectional loading process. The microwear pattern observed on the teeth of P. robustus also aligns with this hypothesis, suggesting that their chewing method may have been adapted to a particular type of food that required different jaw motions than those used by other hominins.
These findings have broad implications for understanding how food processing influenced the evolution of hominin anatomy. The morphology of the jaw and teeth is not solely determined by the type of food consumed but also by the mechanical forces involved in chewing. This insight into chewing mechanics helps to clarify why certain species evolved specific dental features, such as larger molars or thicker enamel, and how these features were related to their diet and behavior. It also provides evidence that the process of mastication, or chewing, might have been just as important in shaping the evolution of early humans as the foods they ate.
In light of these discoveries, some scientists argue that paleoanthropologists might not have always been asking the right questions about the fossil record. Traditionally, much of the focus has been on reconstructing what extinct hominin species ate based on their tooth wear patterns, the shape of their jaws, or isotopic analysis of their bones. While these methods can provide valuable information about diet, the way in which early hominins chewed their food—the mechanics of mastication—has often been overlooked. By focusing more closely on how different species masticated their food, researchers can gain a deeper understanding of their dietary ecology and the evolutionary pressures that shaped their physical adaptations.
Gabriele Macho, a paleoanthropologist at the University of Oxford, suggests that examining the mechanics of chewing might be just as important as understanding the types of food our ancestors ate. She argues that the mechanical properties of mastication—how the jaw, teeth, and muscles work together during chewing—can reveal much more about the daily lives of early hominins than previously thought. In addition to providing insight into diet, these findings could also shed light on the evolution of jaw and tooth morphology across different hominin species, offering a more nuanced view of how our ancestors adapted to their environments.
For anatomists and dental researchers, understanding the mechanics of fossilized jaws can also have practical applications for modern human dentistry. Viviana Toro-Ibacache, a co-author of the study and a dentist at the University of Chile, emphasizes the importance of studying the jaws of extinct hominins from a medical perspective. By better understanding how early human ancestors masticated and how their jaws worked, researchers can gain valuable insights into modern human dental pathologies, such as malocclusions (misalignment of the teeth) and temporomandibular joint disorders. By tracing the evolution of dental features and jaw mechanics, scientists may one day be able to improve treatments for these common dental issues.
The use of non-invasive imaging techniques like CT scanning and 3D shape analysis represents a significant advancement in paleoanthropological research, allowing scientists to study fossilized remains with unprecedented detail and accuracy. These techniques have opened up new avenues for understanding the biomechanics of chewing and its role in the evolution of hominins. As technology continues to evolve, researchers may be able to refine these methods further, providing even more insights into how our ancestors processed food and how this influenced their anatomical development.
More information: On the relationship between maxillary molar root shape and jaw kinematics in Australopithecus africanus and Paranthropus robustus, Royal Society Open Science, rsos.royalsocietypublishing.or … /10.1098/rsos.180825