We Are What We Ate: Diet and Human Evolution

At a key moment in human evolution, our diet expanded and became more diverse, setting the stage for humans to draw on a wider range of food sources to feed expanding brains.

Four academic papers published together in the June 3, 2013 issue of the Proceedings of the National Academy of Sciences report on new methods of studying the carbon found in ancient teeth, going back more than 4 million years.  Ancestors living then ate pretty much what apes eat today, a diet of mostly leaves and fruits.  Then about 3.5 million years ago, a major shift occurs. 
Caption:This is an artist's representation of Paranthropus in southern Africa more than 1 million years ago.  Credit:Illustration courtesy ArchaeologyInfo.com/ScottBjelland.  Usage Restrictions: None

  

The old food sources remained in use, but new sources are added.  Researchers came to this conclusion by analyzing the carbon isotopes still present in ancient teeth.  After examining 175 specimens from 11 different species, they concluded that a key shift occurred at about 3.5 million years ago.  At that point, at least some of our ancestors were supplementing the usual foods by turning to grasses or sedges—or to the animals that graze on them.  These ancestors, including Australopithecus afarensis (best known as the famous “Lucy”), became more diverse in their food sources.

The earliest known evidence suggests that at about this same time, our human ancestors were making tools and using them to butcher large animals for food.  If these animals ate grasses, the carbon would have entered the human diet that way.  Another possibility is that human ancestors were simply learning to identify other types of plants as food sources compatible with human metabolism.

The main point, however, is that at this critical 3.5 million year transition, human ancestors were become more variable in their diet and in their behavior.  Rather than being locked into one type of food source or one way to pursue food, they were becoming more varied in their diet and behavior.  This made it possible for them to exploit more sources of food, nourish even bigger brains, travel and thrive in new niches, and survive climate change cycles, particularly ancient African cycles of wet and dry periods. 

"We don't know exactly what happened," said Matt Sponheimer of Colorado University and one of the researchers. "But we do know that after about 3.5 million years ago, some of these hominids started to eat things that they did not eat before, and it is quite possible that these changes in diet were an important step in becoming human."

If becoming more varied and adaptable is the same as becoming more human, then this study provides an important insight into this process.  One of the papers (Wynn et al.) concludes with this sentence: “This dietary flexibility implies unique landscape use patterns and malleable foraging behavior within a narrow time from of a single species.”  In other words, they were able to adjust quickly, seizing new opportunities and adapting to environmental changes.