Sometime after humans split away from chimpanzees about 8 million years ago their diet changed. They became meat eaters in a much bigger way. They also shifted from mainly eating fruits and insects to including grasses in their diet. One recent paper dates the eating of grasses by Australopithecus bahrelghazali from Koro-Toro Locality KT12 to about 3 -3.5 million years ago ( about 1 million years earlier than previously thought) while another paper dates regular meat eating to about 1.5 million years ago.
1. Julia Lee-Thorp, Andossa Likius, Hassane T. Mackaye, Patrick Vignaud, Matt Sponheimer, and Michel Brunet, Isotopic evidence for an early shift to C4 resources by Pliocene hominins in Chad, PNAS, Published online before print November 12, 2012, doi: 10.1073/pnas.1204209109
Phys.org —An international team of researchers has found evidence that suggests a human ancestor – Australopithecus bahrelghazali – was eating grass plants almost a million years earlier than most scientists had thought. In their paper published in the Proceedings of the National Academy of Sciences, the team says carbon dating of tooth fossil samples found in Chad indicate early hominins had been dining on a diet heavy in plants that contained 4 carbon atoms (C4), which are typical of grasses or sedges.
A. bahrelghazali stood approximately five feet tall (similar in size to modern chimpanzees) and walked on two legs. It also had a projecting jaw with powerful muscles and large teeth that enabled it to grind plant material to aid digestion. During its time, the part of African where it lived was covered with lakes, floodplains and wooded grasslands, which would lead quite naturally to a change in eating habits if a pattern of living on the ground as opposed to trees developed. Grasses and sedges are generally high fiber foods that also have complex starches and some even have tissue that also offers nutrients, thus, A. bahrelghazali would have been able to survive on such a diet despite not having evolved a sophisticated plant processing digestive system such as that seen with modern cows. The researchers acknowledge that because there is so little fossil evidence to work with, it is possible that the carbon levels found in the tooth fossils came from eating animals that consumed C4 plants, but thus far there is no other evidence to suggest that was the case.
2. Manuel Domínguez-Rodrigo, Travis Rayne Pickering, Fernando Diez-Martín, Audax Mabulla, Charles Musiba, Gonzalo Trancho, Enrique Baquedano, Henry T. Bunn, Doris Barboni, Manuel Santonja, David Uribelarrea, Gail M. Ashley, María del Sol Martínez-Ávila, Rebeca Barba, Agness Gidna, José Yravedra, Carmen Arriaza. Earliest Porotic Hyperostosis on a 1.5-Million-Year-Old Hominin, Olduvai Gorge, Tanzania. PLoS ONE, 2012; 7 (10): e46414 DOI: 10.1371/journal.pone.0046414
Science Daily: …. The discovery, made by a global team of researchers led by Manuel Domínguez-Rodrigo from Complutense University, Madrid, suggests that early human ancestors began eating meat much earlier in history than previously believed. The skull fragment identified is thought to belong to a child somewhat younger than two and shows bone lesions that commonly result from a lack of B-vitamins in the diet. …..
Nutritional deficiencies such as anemia are most common at weaning, when children’s diets change drastically. The authors suggest that the child may have died at a period when he or she was starting to eat solid foods lacking meat. Alternatively, if the child still depended on the mother’s milk, the mother may have been nutritionally deficient for lack of meat.
Both cases imply that “early humans were hunters, and had a physiology adapted to regular meat consumption at least 1.5 million years ago,” say the authors.