Study Debunks Theory About Diet of Earliest Humans

Ruth Schuster
Ruth Schuster
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The original complete skull (without mandible) of a 1.8 million-year-old Paranthropus robustus, discovered in South Africa.
The original complete skull (without mandible) of a 1.8 million-year-old Paranthropus robustus, discovered in South Africa.Credit: Jos Braga / Didier Descouens /
Ruth Schuster
Ruth Schuster

Bite a hard object with enough force and your tooth will chip. So it goes. Now a new study published in the Journal of Human Evolution has debunked a hypothesis about distant human evolution – that the reason a primitive cousin species called Paranthropus had massive back teeth was precisely in order to crack hard nuts and seeds. Our ancestors on the Homo line are thought to have developed the type of puny teeth we still sport today because they ate softer foods and meat, possibly even – hang onto your big-brained hats – cooked.

At least some of that is not so, suggests the study from the University of Otago, New Zealand. It isn’t that they found new specimens of Paranthropus, a sort of “robust australopithecine” of which a few species have been tentatively identified. It’s that the team visited institutions in South Africa, Japan and Britain, studied fractured teeth in more than 20,000 teeth of fossil and living primate species, connected the dots and as anthropologist Ian Towle of Otago (working with Carolina Loch from the Faculty of Dentistry) concluded: the neat picture of Paranthropus cracking hard nuts and Homo-line hominins subsisting on softer food is too neat. The actual picture is far more complex.

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“By individually studying each tooth and recording the position and size of any tooth fractures, we show tooth chipping does not support regular hard food eating in Paranthropus robustus, therefore potentially putting an end to the argument that this group as a whole were hard food eaters,” he says.

Paranthropus lived alongside hominins that were ancestral to us in eastern Africa; evidence of them dates to almost 3 million years ago to just over a million years ago. It may have arisen sooner and survived later, but that’s the evidence to date. From the start of their discovery, in Tanzania’s famed Olduvai Gorge in 1955, scientists were struck by the size of their teeth, and the tininess of the cranium, which had room for a brain about 500 cubic centimeters in dimension. Yours is around 2.5 times bigger.

This study changes a facet of human evolution as we understood it: how Paranthropus ate, and how it didn’t eat, and how that may pertain to us.

The skull of Paranthropus boisei, known as KNM ER 406, photographed at the Nairobi National Museum in August 2012.Credit: Bjrn Christian Trrissen
Note the delicate teeth in the human jawbone from Misliya, 200,000 years ago.Credit: Gerhard Weber/University of Vienna

The team qualifies that when you chip your tooth, as opposed to develop a cavity, this is not generally a gradual process, though enamel can develop fatigue and undergo demineralization (which can exacerbate the risk of chipping).

The researchers were surprised to see the “extremely high” rates of tooth fractures in the human fossils, at rates similar to extant primates that eat “hard objects” such as shelled nuts. But this was not the case of the Paranthropus.

“Direct evidence from enamel microwear studies of P. boisei suggests little to no hard object feeding,” the team writes. “In P. robustus, higher enamel surface complexity may indicate hard foods were consumed more frequently, potentially in the context of ‘fallback foods.’”

So what do we have? Two different types of Paranthropus that may, according to their tooth wear, have subsisted on different foods. Carbon isotope analysis indicates the same. So what did they eat? Probably a lot of grasses and sedges, among other things.

The tooth-fracture analysis is based on the assumption that the nature and area of the fracture can attest to the mechanical structure of both the tooth enamel and the object being bitten.

Here is a video of a capuchin monkey who can do better than that. He is using a stone tool to hammer nuts.

All in all, the researchers were surprised by the sheer prevalence of fractures in the human tooth fossil record – akin to that of hard-object eating primates alive today, while Paranthropus evinced extremely low levels of fracture, similar to primates that eat soft fruits or leaves, Towle explains.

“Although in recent years there has been a slow acceptance that another species of Paranthropus, Paranthropus boisei, found in East Africa, was unlikely to have regularly eaten hard foods, the notion that Paranthropus evolved their large dental apparatus to eat hard foods has persisted. Therefore, this research can be seen as the final nail in the coffin of Paranthropus as hard object feeders,” he stated.

Paranthropus boisei - steps of forensic facial reconstruction.Credit: Cicero Moraes

What about cooking? There is no question that our ancestors and other hominins were using fire, barbecue-style at least, going back a million years. Some even argue that fire was tamed in prehistoric Israel, by hominin communities on living on the coast around Mount Carmel around 350,000 years ago. So some cooking was apparently happening in our prehistory, at least at some point, and it the practice have had marked influence on our evolution, not only because we could extract more nutrients from the foods but because our teeth and jaws could be weaker than when we subsisted on raw stuffs. In addition, some argue that cooking food kickstarted the evolution of the human big brain

Also: It is true that throughout human evolution, our brains grew bigger and our molars grew smaller. But our brains and teeth did not co-evolve, dental anthropologists demonstrated in 2017.

Was Paranthropus ancestral to us? The thinking is not; that it was a parallel line to the Homo line. In any case, if the Paranthropus species didn't subsist on hard foods and that can't explain their giant back teeth, a different explanation needs developing for the diminution of the back teeth along the human line. Perhaps, the team suggests, Homo-line dentition grew smaller as other parts of the brain expanded to create the great and wonderful human brain; and/or in parallel, perhaps our enamel underwent evolution too, possibly becoming more robust, to protect our puny molars against the vagaries of diet and life. And nuts. If one throws a rock at you, it can break your teeth.

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