The Neanderthals and the Mystery of the Missing Zinc
Ruth Schuster
Analysis of a Neanderthal in Spain supports previous research by Israeli scientists on how they could survive the toxic habit
What exactly is he eating?Credit: Gorodenkoff/Shutterstock.com
What did Neanderthals eat? The major human variants in the last two million years were apparently omnivores with a deep carnivorous streak. But there is a riddle regarding Neanderthals specifically.
Analyses of Neanderthal remains, including in a 2022 study by Klervia Jaouen at the Max Planck Institute for Evolutionary Anthropology and colleagues, suggest that Neanderthals were more carnivorous than obligate carnivores such as the cat. That is in keeping with previous research. But it makes no sense.
Obligate carnivores must get effectively all their calories from meat. Cats are obligate carnivores: they cannot digest carbohydrates at all. Dogs are facultative carnivores, meaning they can handle some plant matter but cannot thrive without meat – ancestral dogs didn’t join our human households because we were sharing spinach.
Humans are omnivores: if it moves, we’ll eat it; if it doesn’t move, we’ll eat it. However, if we get more than 35 to 40 percent of our calories from meat, we get sick. Our metabolisms are not equipped to remove large amounts of nitrogen (a byproduct of digesting protein). Symptoms of protein poisoning include fatigue, nausea, vomiting, dulled appetite, diarrhea and, ultimately, death.
We are very close to the Neanderthal, genetically speaking. Yet the 2022 study analyzed the teeth of a specific Neanderthal who lived in Gabasa, Spain, 50,000 years ago reached the same conclusion as previous work – he apparently gorged on meat.
In a follow-on paper published in PNAS, Miki Ben-Dor and Prof. Ran Barkai of Tel Aviv University do not purport to solve the conundrum, but note that the original authors neglect a key element in early human nutrition: the fat (a point to which the original authors agree). Ben-Dor and Barkai also point out that the 2022 paper supports a thesis they have been propounding - about the role of fat in human evolution.
The Neanderthal and the steak
Theoretically, it’s possible that Neanderthals adapted to digest meat better than sapiens can. One of the studies suggesting that very thing was by Ben-Dor, Barkai and Avi Gopher in 2016. Neanderthals’ barrel-shaped thorax and differences in their pelvic structure suggest an enlarged liver and urinary system to cope with a higher consumption of meat, they postulate.
But even if Neanderthals could digest a deer better than we could, to what degree? It’s not plausible that they were more carnivorous than cats as one could infer from the new data published by Jaouen et al. The Gabasa Neanderthal’s zinc-66 isotopic ratio was so low that it outshines obligate carnivores.
Briefly, the ratio between zinc 66 and 64 in our teeth indicates what we ate, because animal muscle is high in zinc-64 while plants are high in zinc-66.
When herbivores eat plants, they get tons of zinc-66 but lose some of that while digesting. Then when carnivores eat herbivores, they lose yet more. “The body digests and absorbs the zinc isotopes differently,” Ben-Dor explains: in each phase of digestion, from the herbivore eating a plant to the carnivore eating a herbivore, more zinc-66 gets lost.
Theoretically Neanderthals should have an interim reading of zinc isotopes, in compliance with omnivory – perhaps tending toward low zinc-66 because they may have loved meat but were not the Komplete Karnivore; they couldn’t have been.
Zinc oreCredit: Panayot Savov / Shutterstock.com
Yet the zinc-66 isotope in the Gabasa Neanderthal’s teeth was even lower than that of the carnivores. And whatever the size and state of his liver, it just makes no sense – especially as we now know Neanderthals ate plants too. Another study found they cooked their plants.
Other research at one Siberian Neanderthal site and eight western ones found anomalously high nitrogen readings, another hallmark of an extremely heavy meat diet, which is also a mystery.
The mammoth anomaly
Among the explanations Jaouen and colleagues suggest for both the zinc and nitrogen conundrums was metabolic weirdness in Neanderthals. Or, possibly the Neanderthals ate mainly mammoth and other mega-animals who themselves had elevated nitrogen because they ate desert plants (most plants need to get nitrogen from the soil, but some desert plants can “fix” the nitrogen they need from the air).
One snag with this theory is that mammoth remains at Neanderthal sites are scarce, Jauoen and the team say. There could be plenty of explanations for this, one being that mammoths did not necessarily throng Neanderthal sites. Another possibility is that the enormous elephantids were killed elsewhere and the hominins would cut off pieces to take back to the kiddies at the cave.
Ben-Dor cavils at the characterization that signs of mammoth consumption by Neanderthals are scarce. Bones per se may be scarce at Neanderthal sites, but if one checks site by site, one winds up with a lot of sites with mammoth remains, he says. Barkai and Ben-Dor are confident that prehistoric humans ate as many elephantids as they could, and gained a major proportion of their calories from fat. Actually their diet consisted of lots of meat, some plants and lots and lots of fat.
Ben-Dor adds: given their intake of fat to supplement their calorie intake from meat, they may not have needed to eat many of those pesky plants.
Adipose tissue, the fat, has no zinc in it. The anomaly in the Neanderthal is zinc isotope ratios that belie belief and gorging on fat wouldn’t change that ratio, Ben-Dor stresses.
But it would explain how Neanderthals (and any other hominin) could subsist largely on animals, augmenting their diet with some plant matter, without poisoning themselves and in fact, in separate papers Ben-Dor and Barkai argue that the Homo lineage has been a super-predator for at least two million years. They argue that Homo erectus was an alpha predator; and they have shown that mean animal size in archaeological sites has decreased by more than 98 percent (!) in the last 1.5 million years.
Why animals shrank is hard to nail down, but predation by ancient hominins and humans clearly contributed to some mega-fauna extinctions. It is easy to imagine we ate them to death – and as the big animals died out, we had to refine our hunting strategies in order to catch smaller, fleeter animals.
Barkai and Ben-Dor have shown that hominins predating modern humans were smashing elephant and other big-animal long bones to get at their fat-rich marrow hundreds of thousands of years ago. They have even suggested that ancient hominins would stash long bones in cool spots to obtain the marrow later, even weeks after the animal had been killed.
So perhaps Neanderthals didn’t eat proportionally more meat than other carnivores but did eat copious amounts of fat. Small mammals are not blessed with much fat. They are lean.
And as the last wild megafauna in Europe died out about 40,000 years ago, so did the Neanderthal, who may have depended on their fat to survive.