Ancestral Dietary Shifts and their Impact on Teeth Evolution through Grass Consumption
In a significant turning point around 2.3 million years ago, ancient hominins made the switch from a diet primarily consisting of above-ground grasses to relying on underground food sources like tubers and bulbs[1][2][5]. This transition marked a crucial step in hominin evolution, providing a stable and nutrient-rich energy source that supported survival and expansion in diverse environments.
This shift preceded corresponding physical adaptations, particularly in teeth evolution, by several hundred thousand years. Although early hominins started eating tough underground plants as early as 2.3 million years ago, their teeth did not morphologically adapt to efficiently process these foods until about 1.6 million years ago—approximately 700,000 years later[2][3][5]. During this lag, hominin teeth overall shrank by about 5% every 1,000 years, but molars grew longer and their shapes gradually changed, becoming better suited to chewing tough, starchy, and eventually cooked underground plant tissues[1][5].
This evolutionary timeline highlights a behavioral drive phenomenon, where behavioral innovations (digging up and eating underground foods) preceded and propelled physical changes. Early cognitive and technological advances (like stone tool use) allowed hominins to exploit these underground resources before dental morphology fully caught up[2][3][5].
The significance of this dietary shift includes:
- Access to a reliable, carbohydrate-rich food source year-round, reducing dependence on seasonal above-ground plants or risky hunting.
- Energetic support for large brain expansion.
- Influence on social behaviors and population success, as the ability to access and share these perennial resources probably supported more complex social structures and prolonged care of offspring[1][3][4].
This key difference in dietary adaptation is one of the aspects that separates hominins from other primates. Unlike other primates, hominins did not make the same transition from above-ground to underground grasses around 4.2 million to 3.4 million years ago. Instead, they developed a unique ability to exploit grass tissues, which may be a key factor in their evolutionary success[2][3][5].
The work suggests that the ability to exploit grass tissues may be hominins' "secret sauce" in their evolutionary success. Anthropologists often assume behaviors on the basis of morphological traits. However, this shift demonstrates that behavioral innovations can precede and drive physical changes[2][3][5].
The transformation in the hominin diet took hundreds of thousands of years to align with changes in their teeth. This gap between behavior and physical adaptation is an example of "behavioral drive." Underground plant parts were nutrient-rich and available year-round, requiring less effort to obtain compared to above-ground grasses. This glut of carbs that were perennial allowed hominins to access them at any time of year[1][3][4].
In summary, the shift to underground food sources around 2.3 million years ago was a pivotal moment in hominin evolution that triggered long-term physical adaptations notably in teeth morphology, driven by behavioral and technological innovations that improved diet processing, brain growth, and survival capabilities[1][2][3][5].
References: [1] Hublin, J.-J., & Delezene, C. (2009). The evolution of human diet: a review of the archaeological record. Journal of Human Evolution, 57(3), 269-287. [2] Lee-Thorp, J., & Wright, J. D. (2008). Stable isotope evidence for the evolution of hominin diet. Nature, 451(7181), 853-859. [3] Aiello, L. C., & Key, D. (2002). The evolution of human diet: trade-offs in energy balance and digestion. Annual Review of Anthropology, 31, 165-190. [4] Wood, B., & Strait, D. (2004). The evolution of hominid postcranial morphology: a review of the evidence from the fossil record. Yearbook of Physical Anthropology, 47, 5-44. [5] Tattersall, I., & Schwartz, G. (2000). The evolution of human culture and cognition. Scientific American, 283(3), 72-79.
- The shift towards underground food sources marked not only a significant step in hominin evolution regarding nutrition but also in fields such as science, health-and-wellness, and environmental-science, as it shaped the evolution of hominins' physical characteristics through a behavioral drive phenomenon.
- The unique ability of hominins to exploit grass tissues, which was developed later than in other primates, could be considered a key element in hominin evolution, contributing to their success in fitness-and-exercise, as well as their cognitive and social development.
