Some anthropologists have noted early evidence of meat-eating around the time Homo erectus evolved, which sported an exceptionally large brain for a creature of its size. The apparent correlation between these events has led both experts and ordinary observers to endorse the “Meat made us human” hypothesis. However, a reanalysis of these sites casts doubt on these conclusions, showing the association may be an illusion based on biased site sampling.

The idea that large brains need animal protein (and a few micro-nutrients) to grow is so beguiling that the Australian Meat and Livestock industry ran a major campaign on it, fronted by Sam Neill fresh from playing Jurassic Park paleontologist Alan Grant. 

Inevitably, vegetarians questioned the tagline of “Red Meat – We Were Meant To Eat It”. Now, a paper in Proceedings of the National Academies of Sciences reveals that the campaign's critics may have been right all along.

“Generations of paleoanthropologists have gone to famously well-preserved sites in places like Olduvai Gorge looking for — and finding — breathtaking direct evidence of early humans eating meat, furthering this viewpoint that there was an explosion of meat eating after 2 million years ago,” lead author Dr Andrew Barr of George Washington University said in a statement. 

There are, however, older locations that also provide evidence for meat consumption.

The researchers looked at the 59 sites in East Africa where human remains dating from 2.6 to 1.2 million years ago have been found. Most of these sites show evidence of meat being part of the human diet in the form of animal bones with stone cut marks, but this doesn't necessarily increase over time.

To double-check the conclusion, the team ran the numbers using the number of sites where cutmarks appear, the number of total bones with cutmarks in a particular period, and the persistence of cutmarks across stratigraphic levels. Each time they compared the results with the amount of digging done at the site. They found smaller-brained australopithecines were already eating meat at the beginning, and there is no evidence that increased with Homo erectus' rise.

So if meat eating was a constant part of our ancestors' diet, why the perception that it coincided with the great expansion in brain size? Perhaps some people had just rewatched the opening scenes of 2001: A Space Odyssey too often, but there's also a less embarrassing explanation: Sites dating to just under 2 million years ago have been particularly heavily studied.

If carnivory was a constant – but possibly modest – feature of the human diet throughout this period, cut bones will be widespread, but you only find them where you look. With more intensive efforts focused on H. erectus sites, it's inevitable lots of marked bones were found there. Without considering the sampling issues, anthropologists jumped to the wrong conclusion, one the meat industry was only too happy to amplify.

“I’ve excavated and studied cut marked fossils for over 20 years, and our findings were still a big surprise to me,” said the Smithsonian's Dr Briana Pobiner. 

Fruits and berries don't fossilize as well as bones, so we have very little idea of whether meat was a staple of H. erectus' diet, or an occasional treat.

It's possible that meat consumption had something to do with our ancestral brain spurt, since their guts shrank around the same time – but other theories are equally plausible, including the harnessing of fire and increased contributions from grandmothers.

“I would think this study and its findings would be of interest not just to the paleoanthropology community but to all the people currently basing their dieting decisions around some version of this meat-eating narrative,” Barr said. Well, at least to those without a vested interest.