Study shows grassier diets for early humans

University of Utah geochemist Thure Cerling spearhead a set of four new studies that revealed early humans and their ancestors and relatives made a surprising dietary switch some 3.5 million years ago, changing from an ape-like diet of mostly leaves and fruits from trees and shrubs to a grass-based diet of grasses, sedges and, perhaps in later stages, meat from grass-eating animals. Almost two dozen scientists from numerous institutions conducted the new research.
University of Utah geochemist Thure Cerling spearhead a set of four new studies that revealed early humans and their ancestors and relatives made a surprising dietary switch some 3.5 million years ago, changing from an ape-like diet of mostly leaves and fruits from trees and shrubs to a grass-based diet of grasses, sedges and, perhaps in later stages, meat from grass-eating animals. Almost two dozen scientists from numerous institutions conducted the new research.
Four new studies led by the U inspect the diet of our human ancestors, predicting that roughly 3.5 million years ago, humans expanded their diet from leafy vegetables and fruits to tropical grasses and possibly roots.
The research process used in the study is less than 20 years old. The carbon isotopes from fossilized tooth enamel can help determine, to a certain extent, what ancient humans ate. Small amounts of enamel are drilled from already broken teeth, and the powder is examined in a mass spectrometer to see if the enamel contains particular types of carbon that are specific to certain types of plants.
Thure Cerling, professor of geology and geophysics, has been working in Kenya for over 40 years with other anthropologists and said it took 10 years to convince fellow scientists that the method was effective.
Humans originally ate leaves, vegetables and grains such as wheat, barley and rice. Humans also ate sedges ­­— perennial plants that resemble grasses and grow in shallow water. They include plants such as water chestnut, papyrus and sawgrass. While the nutritional difference between these two crops is not important, the means that prehistoric humans used to attain these plants is.
Until researchers know the entirety of the ancient human’s diet, it is difficult to determine an implication to the studies. However, the research proves that humans were exploring outside of their small forested habitats. If humans were obtaining resources from the savanna, they must have been traveling, and by doing so, they may have sparked what has been a continuous curiosity ever since.
Matt Sponheimer, an anthropology professor at the University of Colorado at Boulder, has been interested in this research for about 20 years.
“We now have a better idea of what this change was. We also have evidence that the consumption of C4 or CAM plants was directly related to changes in masticatory morphology, which is pretty key … this morphology largely separates one early hominin from another,” he said in an email.
For example, chimpanzees often travel over savanna landscapes, but rather than seeing the plants as food, they recognize them as obstacles to overcome before they reach their preferred foods growing in the forests.
It is possible that the variety of early humans diet led to the wide range of food that modern humans consume. Sedges are identified as a C4 carbon type, while forest leaves are C3. The ratio of C4s to C3s becomes more and more balanced as humans evolve. 4.4 million years ago humans ate mostly C3 grasses, 2 million years ago humans ate 35 percent C4 grasses, and 10,000 years ago in Turkana, Homo sapiens teeth reveal an even split between C3 and C4 grasses, that is almost identical to the current North American’s ratio.
“We know much better what they were eating, but mystery does remain,” Cerling said.
Fish and other types of meat leave tooth signals identical to grass, so the researches are unsure if human ancestors were strictly herbivores or if they consumed meat. Additionally, they do not know why human ancestors did not start exploring the savannas earlier than 4 million years ago, when grassy savannas were widespread by 6 to 7 million years ago.