Skull of “Nutcracker Man” (Source: University of Oxford/Donald C. Johanson)Nuts are in the news: a recent study found consumption of nuts lengthens life. Another study found that 70 percent of women can protect their kids from nut allergies by simply eating nuts during pregnancy.

But the most recent study, published in PLOS One, is the most groundbreaking to anthropologists, as it offers evidence for a big reason our bodies are so nuts for nuts.

They are apparently almost all our big brains needed to survive— thus almost all we ate— from 1.4 to 2.4 million years ago.

“My colleagues are a bit shell-shocked, but comments so far are overwhelmingly positive,” Oxford University paleoanthropologist Gabriele Macho tells Bioscience.

University of Utah geochemist Thure Cerling, whose 2011 paper on the topic came up to a different conclusion (based on other evidence), agrees. "This adds considerably to our understanding of early hominin diets."

Macho’s group reports in PLOS One that Paranthropus boisei, an ancient relative of modern humans living in East Africa 1.4 million to 2.4 million years ago, lived up to their nickname. The species was dubbed “Nutcracker Man” by many anthropologists due to its large jaw and huge molar teeth. Many believed P. boisei ate largely nuts because of that jaw.

Yet recent analyses of its teeth seemed to conclude that the teeth did not undergo the damage they should from eating hard legumes. Other studies on the teeth have suggested these relatives of humans largely lived on C4 plants, like grasses.

But could large brains like theirs— and ours— survive solely on grasses? There was much debate. The species had survived for a million years, which is a long time for big brains to go without some critical proteins.

So Macho examined modern baboons in a Kenya environment not unlike that in which P. boisei resided. She studied young baboons, as young ones need more nutrients than older ones. The supply of nutrients needed by the young animals was presumably similar to the supply our larger-brained relatives required.

Cyperus Sculentus plant, also known as chufa or tigernut. (Source: Wikimedia/Dr. Stanley Kays)She discovered that year-old baboons consume massive amounts of tough bulbs at the end of C4 plants, known as tiger nuts. The nuts are still eaten by people today. They provide high amounts of vitamins, minerals and fatty acids key for big brains. Indeed, they are called horchata when made into popular drinks in some Spanish-speaking nations.

After crunching numbers, Macho estimated P. boisei could, in three hours, collect enough tiger nuts— just as adult baboons can— to provide it with 80 percent of its daily calorie intake. P. boisei’s diet was thereafter likely supplemented with fruits and insects.

The jaws and teeth of P. boisei expressed features that suggest the species repetitively chewed its food; that it did not swiftly demolish hard objects. Tiger nuts contain starches that are abrasive, and would require exactly this type of chewing.

For Macho, the diet of the baboons reconciled all the apparent dueling mysteries regarding Nutcracker Man.

“Perhaps the biggest surprise was how simple it is to explain all aspects of P. boisei peculiar morphology, once things started to fall into place,” says Macho, whose work generally focuses on dietary ecology and life history evolution.

Noting that she had “gone ’round and ’round in circles for a long time” over various P. boisei mysteries, she adds: “I now feel that P. boisei is the paleoanthropologist’s equivalent of the ‘Elephant and the Six Blind Men’ story. Only by looking at the picture in its entirety is it possible to sort it out.”

In many versions of that universal parable, a group of blind men touch an elephant to understand what it is. Each feels a different part, from skin to tusk. Then the blind men share their discoveries. They find themselves in total disagreement about what an elephant could possibly be.

It is only when they stop arguing and collaborate, bringing together all their disparate views, that they actually “see” the elephant.

Cerling, whose above-mentioned 2011 paper concluded the Nutcracker Man ate largely grasses, not nuts, welcomes the new study. "It is useful to have candidates - both for and against - as possible diets for the various species of hominins. This study certainly brings up a possible diet that previously had not been considered very plausible as a significant contributor to hominin diets. It is especially useful to see the comparison of nutritive properties of a variety of dietary candidates. I expect this is the beginning of some serious discussions about early hominin diets. I look forward to seeing how it all plays out."