How'd We Get Here?

Video summary · 12:39

Why did ancient human progress explode 10,000 years ago?

Brains weren't the problem. For most of human history the climate changed too often for farming to be worth it. Once it settled down, people around the world started farming at about the same time.

· 5 min read

Your ancestor could do your job

About 2,000 grandmothers back in your family tree there's a woman who could have learned your job in a week. Her people had fire and spears, wore shell necklaces, painted wild pigs on cave walls in Indonesia and crossed open sea to Australia. People like her had been around for 200,000 years and built nothing that lasted. Then, about 10,000 years ago, fields, towns, writing and kings all showed up within a few thousand years. What were they waiting for?

The idea was never the hard part

The usual story is that farming was a clever idea that took a long time to occur to anyone. But foragers know wild plants as well as you know your own kitchen, and nobody had to explain to them that seeds grow. Other pieces existed early too: pottery fragments from Xianrendong Cave in southern China are about 20,000 years old, 10,000 years before anyone there farmed. Farming is a bet. You put food in the ground instead of eating it, and you go hungry through winter rather than eat the seed you're saving for spring. It only pays off if next year looks much like this one, and keeps doing so for years.

A planet that kept changing its mind

Greenland ice cores hold the snow of every year of the last ice age. They show temperatures there jumping by 10°C or more within a few decades, about the difference between Oslo and Rome within one working life, and this happened more than 20 times. These swings are called Dansgaard–Oeschger events, after Willi Dansgaard and Hans Oeschger. Each time, the world warmed fast, forests replaced steppe and the herds left, then over a few centuries it slid back into cold. The same cores show a drier, dustier world. CO₂ was around 180–190 ppm at the coldest point, compared with 260–280 for most of the last 10,000 years. In 1995 the botanist Rowan Sage argued that this alone might have made farming a losing game, because wild grasses grow less in that air.

Schematic of Greenland temperature over the last 60,000 years: repeated sudden warmings and slow coolings during the Ice Age, a cold snap called the Younger Dryas, then a stable Holocene from 11,700 years ago. Ice Age 10°C+ jumps within decades, more than 20 times Calm 60,000 yrs ago 11,700 today warmer →
Schematic, not measured data. This is the pattern the Greenland ice cores show: sudden warmings followed by slow slides back into cold, repeated through the Ice Age, then a climate that mostly held steady from 11,700 years ago. The sharp dip just before that line is the Younger Dryas.

The first villagers who gave up

Some people tried anyway. At Ohalo II on the Sea of Galilee, 23,000 years ago, near the coldest point of the Ice Age, Ainit Snir and colleagues went through about 150,000 plant remains in 2015. Among the wild wheat and barley were the kinds of weeds that grow in planted and harvested ground, so someone there was trying a small experiment. Nothing followed from it. Around 15,000 years ago the climate warmed again, and in the Levant the Natufians built round stone-footed houses and stayed put. Their flint sickles still have a glassy shine from cutting wild cereals, and at Ain Mallaha an elderly person was buried with one hand resting on a puppy. Then, about 12,900 years ago, the Younger Dryas brought back near-glacial cold for about 1,200 years, and the late Natufians seem to have gone back to moving around. At Abu Hureyra in Syria one team argues people responded by planting rye, but that's still debated.

The ice finally held still

11,700 years ago the Ice Age ended for good. The Holocene, the period we live in, is officially pinned to a single depth in a Greenland ice core: 1,492.45 metres down. Around that line Greenland warmed by about 10°C in about 50 years, and then, unusually, it stayed that way. Soon afterwards, around 11,600 years ago, people in southeastern Turkey started carving Göbekli Tepe: rings of T-shaped pillars up to about 5.5 m tall and 10 tonnes, built by people with no known domesticated crops. In 1997 Manfred Heun's team traced domesticated einkorn wheat to wild strains on the Karacadağ mountains nearby.

Four continents, one hour

The same thing happened elsewhere at about the same time. Guilá Naquitz cave in southern Mexico has domesticated squash dated to 10,000–8,000 years ago. Northern China was storing broomcorn millet by about 10,000 years ago. At Kuk Swamp in highland New Guinea, people were tending plants around the same time, and in the Andes squash and peanuts followed. None of these groups knew the others existed, and the last land route into the Americas was going under the sea around 11,000 years ago. In 2014 a review led by Greger Larson counted at least 11 regions where farming began independently. If you squash the roughly 300,000 years of our species (the oldest fossils, from Jebel Irhoud in Morocco, are about that age) into one day, farming starts on four continents within the last hour. In 2001 Peter Richerson and colleagues asked whether agriculture was impossible in the Pleistocene but mandatory in the Holocene. Their answer was yes to both. It hasn't been proven, but the video argues it's the best explanation we have.

If humanity were 30 years old, the stable climate of the last 11,700 years would be only the last 14 months. If humanity were 30 years old… 29 years nobody could count on the next century behaving last 14 months farming, pyramids, every date from school
The calm part is short. 11,700 years out of about 300,000 is roughly 14 months out of 30 years. All of written history fits inside that last stretch.

Nobody voted

Early farming wasn't a better life. When Amanda Mummert's team at Emory University reviewed decades of skeleton studies in 2011, the pattern was the same around the world: as people came to depend on crops, most populations got shorter, had more infections and worse teeth, and their bones show hungry childhoods from years when the harvest failed. People kept farming anyway because a field feeds far more people per square kilometre than a wild valley. Farming villages had more children, who needed more fields, and the foragers next door ended up surrounded. In Europe, ancient DNA shows farming arrived mostly with people descended from Anatolian farmers.

The hole in the story: hippos in London

Between about 130,000 and 115,000 years ago there was another warm period, the Eemian. Britain's summers were warmer than any since, and builders digging at Trafalgar Square in the late 1950s found hippo bones from that time. Our species was around, and burials at Skhul in Israel put some people in wild-wheat country. Nobody farmed. Early ice readings that made the Eemian look unstable turned out to come from folded ice near the bottom of the sheet. The explanations left are smaller ones: there were far fewer people, living in scattered groups; the kind of know-how the Natufians had hadn't built up yet; and a warm spell that slowly cooled may not have been the same opportunity as one that stayed steady. We don't know which of these mattered most. Meanwhile, anyone with a 30-year mortgage or tulip bulbs planted in October is assuming next year will be like this one, and that assumption is only about 11,700 years old.

Chapters

  1. Your ancestor could do your job
  2. The idea was never the hard part
  3. A planet that kept changing its mind
  4. The first villagers who gave up
  5. The ice finally held still
  6. Four continents, one hour
  7. Nobody voted
  8. Hippos in London
  9. Your dentist appointment