Evrim Yazgin
Cosmos science journalist
Palaeontologists may have finally filled a gap in the story of human evolution – and it may upend previously-held beliefs about how we got our big brains. The key is in ancient tooth enamel.
Millions of years ago, early hominins relied on eating plants for their survival. At some point, however, our ancestors started to eat meat regularly. It is believed that this transition aided evolution in hominins, and in particular influenced the growth of the brain.
Animal products are easier to digest than unprocessed plant foods. They are also rich in essential amino acids and nutrients, minerals, fatty acids, iron, zinc and vitamin B12.
We know that hominins were eating meat regularly by about 2 million years ago when the genus Homo first evolved in Africa.
This is clear from evidence of stone tools used for butchering and processing meat. There is also ample evidence of animal bones with cut marks that could only have been produced by human ancestor behaviours.
The earliest evidence of hominins butchering large animals dates to 2.9 million years ago at a site on the shores of Lake Victoria in Kenya.
Later in human evolution, species like Neanderthals – which emerged about 250,000 years ago – were top-level carnivores.
But none of this explains when and why this transition took place.
A new study published in the journal Science describes how palaeontologists measured the levels of different isotopes in enamel from fossilised teeth. This allowed them to assess how much meat our ancient ancestors were eating.
The team focused on Australopithecus fossils from South Africa’s Sterkfontein Caves. About 3.5 million years old, these belong to some of the oldest human ancestor species discovered.
The study looked at the levels of nitrogen isotopes in the enamel from the fossil teeth. Nitrogen has 2 stable isotopes – nitrogen-14 and nitrogen-15. The numbers 14 and 15 refer to the number of protons and neutrons in the atomic nucleus. All nitrogen has 7 protons, but nitrogen-14 has 7 neutrons while nitrogen-15 has 8 neutrons.
Both nitrogen isotopes occur in nature but in varying amounts.
Predators have more nitrogen-14 in their bodies compared to herbivores, as the isotope accumulates in the food chain.
The team’s isotopic analysis of the Australopithecus enamel revealed a signature similar to that of herbivores. The ape-like early hominins were mostly eating plants. There was little to no evidence of meat consumption.
“Our data do not preclude occasional consumption of meat or other animal resources, similar to that observed in some modern nonhominin primates, including capuchins (Cebus or Sapajus), baboons (Papio), and chimpanzees and bonobos (Pan),” the authors write.
The researchers say that their findings may challenge the notion that meat-eating was a main driver for human traits such as larger brains, though more research is needed.
