In a recently published study, scientists from Dartmouth College revealed findings that provide insights into the evolutionary trajectory of early hominins. Spearheaded by postdoctoral researcher Luke Fannin and senior author Nathaniel Dominy, the research investigates the dietary habits of ancient humans and how these preferences may have influenced the evolution of human teeth and morphology.
Around 2.3 million years ago, hominins experienced a dietary shift from consuming grass grains to eating the underground parts of grasses, such as tubers and bulbs. This shift coincided with the emergence of Homo rudolfensis and Homo erectus and marked a departure from the preferences of other primates of that time. The isotopic analysis of fossilized teeth suggested that this transition likely provided an advantage by offering energy-rich carbohydrates with minimal competition from other animals.
The researchers' analysis of isotopic signatures in fossil teeth demonstrated dietary shifts long before physical adaptations occurred. This concept, known as "behavioral drive," suggests that beneficial behaviors, such as new dietary habits, can precede and trigger morphological changes. The study offers fossil record evidence suggesting that adaptations in feeding behavior preceded anatomical changes, profoundly impacting the evolutionary trajectory of hominins.
The analysis indicated that hominins began consuming grasses and sedges approximately 3.8 million years ago. However, physical adaptations like the restructuring of molar teeth suitable for chewing tougher plant fibers lagged by about 700,000 years. "Anthropologists often assume behaviors on the basis of morphological traits, but these traits can take a long time—a half-million years or more—to appear in the fossil record," said Dominy.
These evolutionary insights suggest that dietary flexibility allowed early hominins to adapt more efficiently by utilizing underground carbohydrate-rich plant parts. "We propose that this shift to underground foods was a signal moment in our evolution. It created a glut of carbs that were perennial—our ancestors could access them at any time of year to feed themselves and other people," suggested Fannin.
Stone tools, a product of early cognitive advancements, complemented this dietary shift by enabling hominins to harvest subterranean plant organs effectively. The isotopic analysis showed that hominins, despite lacking the specialized dental adaptations observed in other grazers, could exploit these underground resources—enhancing their survival and evolutionary success. The ability to adopt a new diet was pivotal, serving as its own evolutionary force with large implications for hominin development, noted Fannin.
Dietary flexibility allowed early hominins to thrive in new environments even before they developed optimal physical traits. Ultimately, these insights into the dietary behaviors of early hominins underscore the evolutionary significance of behavioral innovation prior to morphological changes. "Our ancestors did something completely unexpected that changed the game for the history of species on Earth," stated Dominy.
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