How'd We Get Here?

Video summary · 10:18

How did ancient humans survive deadly winters?

Fire, furs and a cave kept people from freezing. Winter was dangerous for a different reason: by late winter the animals had no fat left, and a person can starve on lean meat with a full stomach.

· 4 min read

Starving on a full stomach

In February 1928, doctors at Bellevue Hospital in New York tested this on a volunteer. Vilhjalmur Stefansson was an Arctic explorer who had lived for years on almost nothing but meat and fish and insisted it had never hurt him. They put him on a metabolic ward and gave him only lean meat, as much as he wanted. By the third day he had nausea and diarrhoea. He wasn't hungry, he was stuffed. When the doctors added fat back to his meals, he recovered within two days. Ice Age hunters went through the same thing in bad springs, with no one to hand them the fat. Some of them, in the hungriest season, even walked away from fresh kills on purpose.

Your liver has a speed limit

Every gram of protein you burn for energy leaves nitrogen behind, and your liver has to turn it into urea to get rid of it. The liver can only work so fast. Most researchers put the limit at around a third of your daily calories, and beyond that waste starts building up in your blood. A hunter on the steppe burning about 3,000 calories a day in the cold can safely get about a third of that from protein, roughly a kilo of lean meat a day. The other two-thirds has to come from something else, and on the frozen steppe in February, the only other thing is fat.

A hunter's 3,000-calorie winter day: at most about one third can come from protein, roughly a kilo of lean meat; the other two thirds must be fat. A hunter's day in the cold ~3,000 kcal Protein max ~1/3 Fat, or nothing ~2/3 liver's speed limit ⅓ of 3,000 kcal ≈ 1 kg of lean meat a day, a big Sunday roast, eaten alone, every day
Why lean meat isn't enough. Past about a third of your calories from protein, the liver can't keep up. In summer berries or honey could make up the rest. In a steppe February, only fat could.

A reindeer's bank account

A reindeer starts winter like someone setting off on a long trip with money in the bank: fat along its back and packed around its kidneys. When snow buries the lichen, it spends its reserves in a set order. Back fat goes first, then the fat around the organs, and last, only when things are desperate, the marrow inside its leg bones. In 1949 the New York researcher E.L. Cheatum published a simple test that wildlife biologists still use: crack the thigh bone and look. White, waxy marrow means the animal was fine. Red, runny marrow, like jam that didn't set, means it had burned through everything. In 1983 John Speth and Katherine Spielmann pointed out that for northern hunters the most dangerous time was the end of winter into spring, when every animal was at its thinnest.

A reindeer spends its fat in order: back fat, then organ fat, then bone marrow last. Cracking a thigh bone shows white, waxy marrow if the animal is fine, and red, runny marrow if it has starved. WINTER SPENDING ORDER 1st Back fat 2nd Organ fat last resort Marrow THE MARROW TEST · CRACK THE THIGH BONE White, waxy animal was fine Red, runny nothing left
Reading a bone like a bank statement. E.L. Cheatum's 1949 test. Ice Age hunters who cracked bones every day would have known what red marrow meant.

The Neanderthal fat factory

People who got through winter treated fat like money and kept it in bone. Marrow is the obvious part, but there isn't much of it. More grease is locked in the spongy ends of bones, and getting it out means smashing bones into thumbnail-sized pieces, simmering them for hours, letting the pot cool and skimming off the fat. For a long time the oldest clear evidence of this was about 28,000 years old. Then in 2025 a team including Lutz Kindler and Wil Roebroeks published Neumark-Nord in Germany. Around 125,000 years ago, Neanderthals at a lakeshore there processed the bones of at least 172 large animals and left more than 100,000 deliberately broken fragments. That's nearly 100,000 years before the next evidence of anyone doing it.

Winter, paid for in autumn

The planning started in autumn, when animals are at their fattest. At Stellmoor, near what's now Hamburg, people about 12,000 years ago waited at a narrow valley on the reindeer route. The remains of about 650 reindeer have been found there, most killed in autumn. You also needed to know which parts were worth the most. In the 1970s Lewis Binford spent time with Nunamiut caribou hunters in Alaska and came back with what amounts to a spreadsheet of which bones held the most marrow and grease. The hunters knew all of it by heart and had never written any of it down. Fat-rich bones went into caches for later, and the tongue and brain, some of the fattiest parts, were highly valued.

The rabbit trap

By late winter the big herds have left or are too thin to be worth chasing. What's left is small and easy to catch, like white hares and ptarmigan, and a hare is almost pure lean meat. Stefansson described what happens next. People in the Canadian north called it rabbit starvation. If you suddenly eat nothing but rabbit, you eat bigger and bigger meals looking for something the meat doesn't have. After a week you're eating several times as much and still feel starved. Then comes diarrhoea, then a weakness that doesn't go away, and over weeks it can kill you. It doesn't feel like starving. You go to sleep full every night and wake up a little weaker every morning. Nobody knows how many Ice Age people died this way, because this kind of starvation leaves no trace on a skeleton.

Why they left the meat behind

At Garnsey in New Mexico, people killed bison in spring a few hundred years ago. John Speth excavated the site in the late 1970s and recorded which bones were carried away and which were left. In spring the bulls were in better shape, and the hunters took from the bulls. The cows had spent winter carrying calves, many were nursing, and a lot of their meat was left where it fell. Across the plains, bison drives killed dozens of animals and left many carcasses barely touched, taking home the tongues and the fat. It looks like waste, but meat that only fills you up isn't worth the walk home. Speth has argued that the people most at risk in a lean-meat spring were pregnant or nursing women, who needed the most and couldn't get it from lean meat.

Now open your fridge

Stefansson was fine in the end. Once he was allowed fat, he and another explorer, Karsten Andersen, ate nothing but meat for a full year under observation and came out healthy. In your fridge today the fat's been trimmed off the steak, the yogurt says 0% in big letters, and there may be a pricey jar of bone broth, essentially a Neanderthal's lunch. For almost all of human history there was never enough fat. We happen to live in the short stretch where the opposite is true.

Chapters

  1. Starving on a full stomach
  2. Your liver has a speed limit
  3. A reindeer's bank account
  4. The Neanderthal fat factory
  5. Winter, paid for in autumn
  6. The rabbit trap
  7. Why they left the meat behind
  8. Now open your fridge