The diets of early relatives of humans likely began diverging from apes approximately 3.5 million years ago, nearly 1 million years earlier than scientists previously estimated, according to a report published Monday.
Using tooth enamel from fossils of early hominids, researchers were able to discover that about 3.5 million years ago, early ancestors of humans began eating grasses and other low-lying plants – and in some cases, perhaps meat, unlike apes of the time period. Matt Sponheimer, a professor of anthropology at Colorado University—Boulder and author of one of four studies published in Proceedings of the National Academy of Sciences exploring the subject, says the development was "an important step in becoming human."
Sponheimer and his team used chemical residues on dental records from approximately 175 fossilized specimens from 11 different hominids between 1.3 and 4.4 million years old. Zeresenay Alemseged, a researcher at the California Academy of Sciences and author of two of the papers published boils the process down: "What we have is a chemical information on what our ancestors ate, which in simpler terms is like a piece of food item stuck between their teeth and preserved for millions of years."
Sponheimer says that the findings open up as many questions as they answer.
"There is much here that changes our understanding of various human antecedents," he says. "For the earliest [human ancestors], the surprise is that the composition of their diets is so similar to that of chimpanzees. As we got later in time, the surprise is how little the diets resemble those of living apes."
Researchers aren't sure exactly what happened to cause the divergence in diets. Several theories suggest that rapid climate change or competition from other hominids could have led early humans to seek out alternative nourishment, but Sponheimer says the reason still remains largely a mystery. It's also unclear when early human ancestors began eating meat, a topic that remains hotly debated in the anthropology community.
"Everyone would like the dietary expansion to be linked to climatic and environmental change, and perhaps it was, but our evidence for this is rather weak at present," he says. "There is probably no area of [early human ancestor] dietary studies that evokes stronger feelings than the origin and elaboration of meat consumption and hunting. Personally, I believe that we know far less about this topic than is generally believed, although we have good reason to believe that a number of [our early ancestors] did eat meat from time to time. Whether meat constituted 1 percent or 50 percent of the diet is much harder, and at present, almost impossible to say."
Though scientists are piecing together diet information from dental records, ancient tools discovered and the bones of butchered animals, Sponheimer says anthropologists are still stumped about the diets of many human ancestors.
"Determining what animals did a few million years ago is an uphill battle without a time machine," he says. "It's pretty clear that we need new tools if we are to make a coherent story from the current lines of evidence."