Human ancestors changed diet 3.5 million years ago

Human ancestors expanded their menu 3.5 million years ago, adding tropical grasses and sedges to an ape-like diet and setting the stage for our modern diet of grains, grasses, and meat and dairy from grazing animals, new research has claimed.
In four new studies of carbon isotopes in fossilised tooth enamel from scores of human ancestors and baboons in Africa from 4 million to 10,000 years ago, a team of two dozen researchers found a surprise increase in the consumption of grasses and sedges - plants that resemble grasses and rushes but have stems and triangular cross sections.
"At last, we have a look at 4 million years of the dietary evolution of humans and their ancestors," said University of Utah geochemist Thure Cerling, principal author of two of the four new studies published in the journal Proceedings of the National Academy of Sciences.

"For a long time, primates stuck by the old restaurants - leaves and fruits - and by 3.5 million years ago, they started exploring new diet possibilities - tropical grasses and sedges - that grazing animals discovered a long time before, about 10 million years ago when African savanna began expanding," Cerling said.
Grassy savannas and grassy woodlands in East Africa were widespread by 6 million to 7 million years ago. It is a major question why human ancestors didn't seriously start exploiting savanna grasses until less than 4 million years ago.
Direct evidence of human ancestors scavenging meat doesn't appear until 2.5 million years ago, and definitive evidence of hunting dates to only about 5,00,000 years ago.

"The earliest human ancestor to consume substantial amounts of grassy foods from dry, more open savannas may signal a major and ecological and adaptive divergence from the last common ancestor we shared with African great apes, which occupy closed, wooded habitats," said University of South Florida geologist Jonathan Wynn, chief author of one of the new studies and a former University of Utah master's student.

"Diet has long been implicated as a driving force in human evolution," said Matt Sponheimer, a University of Colorado, Boulder anthropologist, former University of Utah postdoctoral fellow and lead author of the fourth study.
Sponheimer noted that changes in diet have been linked to both larger brain size and the advent of upright walking in human ancestors roughly 4 million years ago.

If diet has anything to do with the evolution of larger brain size and intelligence, then we are considering a diet that is very different than we were thinking about 15 years ago, when it was believed human ancestors ate mostly leaves and fruits, Cerling added.