A piece of a child's skull, believed to be 1.5 million years old, offers some of the earliest evidence that early humans were hunters who ate meat regularly, according to scientists.

The two-inch skull fragment, discovered in the Olduvai Gorge in northern Tanzania, has signs of nutritional deficiencies commonly caused by a lack of meat in its owner's diet, leading scientists to believe that early humans needed meat to thrive, according to a study published in the journal PLoS ONE

A team of anthropologists led by Manuel Domínguez-Rodrigo, from Complutense University, Madrid, said that the latest discovery also suggests that our ancient ancestors began eating meat much earlier in history than previously thought. Researchers say that the piece of bone belonging to a 2-year-old child and shows bone lesions that are commonly found in people who lack vitamin B in their diet.

Past studies have suggested that early hominoids ate meat, but researchers were unsure whether meat was a regular part of their diet or was only consumed sporadically. However, researchers say that the latest discovery of the bone lesions present in this skull fragment suggests that meat was a regular part of early human diet and not consuming enough of it could lead to anemia.

Researchers said that nutritional deficiencies like anemia are most common at weaning, when a child's diet changes from breast milk to other sources of nourishment. Domínguez-Rodrigo and his team say that the child may have died at a period when he or she was starting to eat solid foods lacking meat. They say that, alternatively, if the child still depended on the mother's milk, the mother may have been nutritionally deficient for lack of meat.

Researchers said that the evidence showed that the child's diet was deficient in vitamin B12 and B9 and probably died from it, and that meat seems to have been cut off during the weaning process. However, both cases indicate that "by at least 1.5 million years ago early human physiology was already adapted to a diet that included the regular consumption of meat," researchers wrote.

Researchers say that the latest finding sheds new light into the evolution of human physiology and brain development. Charles Musiba, associate professor of anthropology at the University of Colorado Denver, who helped make the discovery, said that the movement from a largely plant-eating lifestyle to a meat-eating one may have provided hominins, including Homo sapiens, the protein needed to grow their brains.

Some researchers have argued that we became human when we became carnivorous-omnivorous creatures. "Meat eating is associated with brain development," Musiba said in a statement. "The brain is a large organ and requires a lot of energy. We are beginning to think more about the relationship between brain expansion and a high protein diet."

Musiba said that humans are one of the few surviving species with such a large brain to body size ratio, and compared to chimpanzees, our closest living relatives, humans consume far more meat and have significantly greater brain capacity. Musiba said that our meat eating was what separated us from our distant cousins. "The question is what triggered our meat eating? Was it a changing environment? Was it the expansion of the brain itself? We don't really know," he said.

"The presence of anemia-induced porotic hyperostosis...indicates indirectly that by at least the early Pleistocene meat had become so essential to proper hominin functioning that its paucity or lack led to deleterious pathological conditions," researchers wrote.

"Because fossils of very young hominin children are so rare in the early Pleistocene fossil record of East Africa, the occurrence of porotic hyperostosis in one...suggests we have only scratched the surface in our understanding of nutrition and health in ancestral populations of the deep past," they concluded.