How Dietary Shifts Shaped the Physical Evolution of Early Humans

As early humans moved from lush forests to open grasslands, they began to eat more plants, especially those rich in carbohydrates. This shift marked a significant change in their diet and ultimately influenced their evolution.

A recent study led by Dartmouth researchers has shown that hominins, our distant relatives, started eating grasses and tubers long before their teeth were adapted to handle such tough foods. This finding is groundbreaking; it reveals that behavioral changes—like a new diet—can happen way ahead of any physical adaptations needed to support those changes.

Researchers analyzed the teeth of ancient hominins and discovered chemical traces from the plants they consumed. Surprisingly, they found that these early humans began incorporating graminoids (grasses and sedges) into their diets about 4 million years ago, well before their teeth evolved to effectively chew them. This gap lasted around 700,000 years, demonstrating how adaptable early humans were, even with physical limitations.

Luke Fannin, the lead researcher, emphasizes this flexibility as a core strength: “Behavior was a powerful agent of evolution, influencing physical features over time,” he explains. Nathaniel Dominy, a senior author of the study, notes that while we often look at physical traits to understand behavior, this research suggests that behaviors can exist independent of physical changes for a long time.

The researchers also compared hominins to other species of ancient primates, like giant terrestrial monkeys, and found that all three groups shifted away from fruits toward grasses. However, around 2.3 million years ago, the diet of early humans changed dramatically, favoring more underground plant parts, such as tubers and bulbs, which are high in carbohydrates.

These underground foods provided a safer and more nutrient-rich option than hunting, which was riskier and required more effort. Moreover, with the development of stone tools, early humans could efficiently gather these foods. This dietary shift might have been key for the growth of their brains, suggesting that our ancestors had access to more energy needed for cognitive development.

Interestingly, as hominins adopted this high-carb diet, their teeth shrank in size but lengthened over time—indicating that their physical evolution was directly linked to their food choices. By around 2 million years ago, species like Homo habilis and Homo ergaster had teeth better suited for processing cooked foods, indicating a significant shift in their eating habits.

Dominy points out that today’s global food systems still rely heavily on grass species like rice, wheat, and corn, showing a long-lasting legacy from those early dietary choices. “This ability to exploit grass tissues might be our unique advantage in the evolutionary landscape,” he states.

This study not only unravels past behaviors but also suggests that our flexible approach to diet might be a crucial factor in human survival. As we continue to evolve, it may be the innovative use of resources that remains a hallmark of humanity.

For further insights, you can read the full study published in Science.

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