You're About to Get Domesticated

It started in secret, seven years earlier

In Stalin's Soviet Union, genetics was banned science. Belyaev lost his job over it in 1948. His older brother Nikolai, also a geneticist, was arrested and shot in 1937.

So in 1952 Belyaev took a train to a fur farm in Estonia and quietly asked the breeder to mate her calmest foxes each winter. The cover story: better fur and more pups. 1959 is only the year it was safe to do it in the open.

Dugatkin & Trut 2017, How to Tame a Fox, ch. 1 · Ptushenko & Ramensky 2023, Genetics

Most tame foxes still look like foxes

The video's fox turns into a dog. The real numbers are smaller. Among the tame foxes, 12 in 100 had the white forehead patch, 9 in 100 a curly tail, and only about 2 in 1,000 floppy ears.

That is still 10 to 17 times more often than in ordinary farm foxes. The dog looks showed up far more, but they never took over.

Trut, Oskina & Kharlamova 2009, BioEssays, table 2

A childhood that stays open longer

Every fox pup has a short window when it meets the world without fear. In ordinary foxes it closes at about 6 weeks. In the tame ones it stays open to 9 weeks or more, which is where dogs are (8 to 12).

That is what "they stay puppies longer" means: the trusting stage of life got stretched. Hold on to that for the last chapter.

Trut 1999, American Scientist

They can read your finger. Nobody taught them.

Point at one of two cups and a dog puppy goes to the right one. Wolves mostly don't get it. Tame fox pups turned out to be as good as dog puppies, and better than ordinary fox pups.

Nobody ever bred them for that. Take away the fear of humans, and paying attention to humans comes for free.

Hare et al. 2005, Current Biology

There is an evil twin

On the same farm, a second line of foxes has been bred the other way: for aggression. They are as hostile to people as the tame ones are friendly.

Crossing the two lines is how geneticists went looking for the DNA behind tameness. In 2018 they found 103 stretches that differ. The top suspect is a gene called SorCS1, which helps brain cells adjust their connections.

Kukekova et al. 2018, Nature Ecology & Evolution

You are 380 times calmer than a chimp. And just as deadly.

Count the fights inside a group. Wild male chimps: about 2,300 attacks per 100,000 hours watched. Men in a human community picked because it seemed unusually violent: 6.

Now count killings between groups. Chimps: 271 deaths per 100,000 a year. Hunter-gatherers at war: 164. Same league. That is the puzzle this theory answers: the hot kind of violence almost vanished, and the cold kind did not move.

Wrangham, Wilson & Muller 2006, Primates

Half of all forager societies had a death penalty

An anthropologist went through the records of 50 hunter-gatherer peoples who live the way everyone lived in the Ice Age. 24 of them report executions, and he thinks that is an undercount, since colonial courts treated them as murder.

The top reason is not theft or sex. It is intimidating the group: repeated killers, tyrants, men everyone feared as sorcerers. And in 6 of 10 societies looked at closely, the job went to a close male relative, so that nobody was left owing revenge. The cousin by the river is in the data.

Boehm 2012, Behavioral and Brain Sciences

The man in the Kalahari had a name

He was called /Twi, and the story was told to the anthropologist Richard Lee. /Twi had killed two people. One man tried to end it alone with a poisoned arrow, and failed: /Twi stabbed a woman and killed her husband. Then everyone shot, in the informant's words, until he "looked like a porcupine".

One correction to the video: it was not only the women who stabbed the body afterwards. It was everybody, men and women. If the whole camp did it, nobody did it.

Lee 1979, The !Kung San, pp. 394-398 · retold in Boehm 2012

Hot and cold run on different wiring

In a cat's brain they sit in two different places. One spot gives defensive rage: hissing, arched back, racing heart. Another gives the quiet stalking attack it uses on a mouse: calm, silent, aimed. Rats have the same split.

That matters for the story. If temper and planning were one dial, you could not turn one down and keep the other. They are two dials. In people, the hot one is held down by serotonin, the same brain chemical the tame foxes have more of.

Siegel & Victoroff 2009 · Wrangham 2018, PNAS

Chimps have killed their own alpha too

"No other animal has ever done this" needs a footnote. In 2011 at Mahale, Tanzania, four males killed their alpha, Pimu. Two of them were his closest grooming partners. In 2013 at Fongoli, Senegal, an overthrown alpha called Foudouko tried to come back after five years on the edge of the group, and was found dead the next morning.

The difference: those were fights that blew up on the spot. Nobody has seen chimps plan one. To agree on Tuesday who dies on Thursday, you need words. That is why the theory puts the start at about 300,000 years ago, when the Jebel Irhoud people already had your face.

Kaburu et al. 2013 · Pruetz et al. 2017 · Wrangham 2021 · Hublin et al. 2017, Nature

Only 54 of the 1,400 skulls are old

The study had 13 skulls older than 80,000 years, 41 from 38,000 to 10,000 years ago, and 1,367 from the twentieth century, from 30 peoples around the world.

That is how fossils work: the older the skull, the fewer there are. The trend is clear, brow down and upper face shorter, but it rests on a handful of very old heads.

Cieri et al. 2014, Current Anthropology · the university's summary

Less testosterone, or fewer ears for it

The authors are careful here. A skull cannot tell you how much testosterone was in the blood. It could be that there was less of it. It could be that the body had fewer receptors listening to it. The bone looks the same either way.

So "big brow = big testosterone" is the short version. The paper's version is "less testosterone action".

Cieri et al. 2014, Current Anthropology

Or maybe it was about eyebrows

In 2018 a team took a scan of an ancient skull from Zambia with a huge brow ridge and shaved the ridge down on a computer. Then they made it bite. Nothing changed. The ridge was far bigger than it needed to be for chewing or for holding the skull together.

Their idea: the ridge was a permanent "don't mess with me" sign. Lose it and you get a smooth forehead with eyebrows that move. Raised in greeting, pulled together in sympathy. A face built for small friendly signals, no hormones needed.

Godinho, Spikins & O'Higgins 2018, Nature Ecology & Evolution

The necklace is twice as old as the video said

Blombos has the famous beads: 41 tiny sea snail shells, each pierced, 75,000 years old. But they are not the oldest. In Bizmoune Cave in Morocco there are 33 shell beads at least 142,000 years old, polished around the hole from hanging on a cord, some with red pigment still on them.

And people were carrying good stone and red pigment 25 to 50 km from its source in Kenya about 300,000 years ago. The same age as the bully by the river.

Henshilwood et al. 2004, Science · Sehasseh et al. 2021, Science Advances · Brooks et al. 2018, Science

Bonobos did it too

Chimpanzees and bonobos are sister species. Chimps are the violent ones. Bonobos settle things with play and sex, and next to a chimp a grown bonobo has the skull of a youngster: small teeth, slight face, hardly any brow.

Same pattern, no humans involved. The researchers call it self-domestication, and it is the word they then borrowed for us.

Hare, Wobber & Wrangham 2012, Animal Behaviour

How you test a face gene without growing a face

The Milan lab took skin cells from people with Williams syndrome (one copy of the patch missing) and from people with the opposite, an extra copy. They turned those cells back into neural crest cells, the travelling embryo cells that build the face.

Then they turned BAZ1B down like a dimmer. 448 other genes went up or down with it, and the cells crawled at a different speed. One gene, conducting hundreds. And more of those genes than chance would give are ones that differ between you and Neanderthals.

Zanella et al. 2019, Science Advances

The mirror image exists too

If losing a copy makes you walk up to every stranger, what does an extra copy do? In a study of 63 children with the duplication, half had social phobia and 29 in 100 had selective mutism: they can talk, but not around people they don't know.

One copy too few, no fear of strangers. One copy too many, too much of it. The patch works like a volume knob.

Mervis et al. 2015, Am. J. Medical Genetics · Kozel et al. 2021, Nature Reviews

In dogs it is the gene next door

The dog study tested 18 dogs and 10 hand-raised wolves: how much attention do you give a human, how keen are you on a stranger? Then it read their DNA across the Williams patch.

The friendliest animals carried extra bits of "jumping" DNA wedged into the genes. Not in BAZ1B itself, but in its neighbours GTF2I and GTF2IRD1, the same two genes doctors link to the friendliness in Williams syndrome.

vonHoldt et al. 2017, Science Advances

You didn't just beat him. You married in.

The oldest modern humans found in Europe come from Bacho Kiro Cave in Bulgaria, about 45,000 years old. Their DNA is 3 to 3.8% Neanderthal. One of them had a Neanderthal in the family fewer than six generations back. A great-great-great-grandparent.

If your ancestors left Africa, about 2% of your DNA is still his. The big guy is not entirely gone.

Hublin et al. 2020, Nature · Hajdinjak et al. 2021, Nature · Prüfer et al. 2014, Nature

His brain was bigger. Yours is rounder.

Scanned skulls: 8 Neanderthals average 1,450 ml, 89 people today average 1,328 ml. About 9% apart, and the two groups overlap a lot.

The clearer difference is shape. His braincase is long, like a rugby ball. Yours is a globe, and it only became one somewhere between 100,000 and 35,000 years ago. Your species had its size long before it had its shape.

Neubauer, Hublin & Gunz 2018, Science Advances

Apes follow your head. Babies follow your eyes.

The idea started in 1997, when two Japanese researchers compared the eyes of 88 primate species. Humans showed the most white and had the widest, most stretched-out eye opening of them all.

Ten years later came the test. A person looks up at the ceiling: sometimes with the whole head, sometimes with only the eyes. Chimps, gorillas and bonobos mostly followed the head. One-year-old babies followed the eyes, almost every time. You were reading eyes before you could talk.

Kobayashi & Kohshima 2001, J. Human Evolution · Tomasello et al. 2007, J. Human Evolution

Paint a chimp's eyes white and chimps read them better

In 2022 researchers showed eye photos to people and to chimpanzees on a touchscreen: which way is this one looking? Both species did better with human eyes than chimp eyes, above all when the picture was small or dim. Far away, in bad light. A hunt.

Then they edited the chimp photos to have clean white around the iris. Both species got better at those too. The white really is a signal booster, even for an ape that doesn't have it.

Kano et al. 2022, eLife

Puppy-dog eyes are a real muscle

Dogs grew their own eye signal. Researchers dissected 6 dogs and 4 wolves. Every dog had a small muscle that lifts the inner eyebrow, the sad, big-eyed look. In the wolves it was a few stray fibres.

Watching 27 shelter dogs and 9 wolves, the dogs pulled that face more often and harder. It makes the eye look bigger and more like a baby's. The researchers' guess: people went soft for it, so the dogs that could do it got looked after.

Kaminski et al. 2019, PNAS

The gentler the species, the paler the eye

A 2022 study lined up primate species by eye colour and by behaviour. Species with paler whites were the ones that share more and tolerate each other more. Across 108 species, paler whites also went with fewer deaths at the hands of their own kind, though that link is weak.

Bonobos fit: next to chimps they are the peaceful ones, and their eye whites are clearly lighter.

Mearing et al. 2022, Scientific Reports · Perea-García et al. 2019, PNAS

Some chimps have white eyes too

At Ngogo in Uganda, researchers went through 1,187 photos of 230 wild chimpanzees. 15 in 100 had white in their eyes. Among babies under a year and a half it was more than half.

So white is not a human invention. What is human is that everyone has it, all of it, for life. One more thing you kept from childhood.

Clark et al. 2023, J. Human Evolution

The tennis ball checks out. For women it is more.

The classic count used about 12,800 skulls from Europe and North Africa. Men went from 1,593 ml at the peak to 1,436 ml today: 157 ml gone. A tennis ball is about 150. Women lost 261 ml.

The man who counted them did not think we got dumber. His explanation: the whole skeleton got lighter and finer, and the skull went with it.

Henneberg 1988, Human Biology

The more we handle them, the smaller the brain

Skulls of 71 cattle breeds against their wild ancestor, the aurochs. How much brain each kind of cattle has lost:

• Bullfighting breeds15%
• Park cattle, left alone18%
• Beef cattle25%
• Dairy cows, handled daily31%

The animals bred to fight kept the most. The ones handled by people every day lost the most. Brain loss follows how tame the job is.

Balcarcel et al. 2021, Proc. R. Soc. B

What exactly went missing

In the sheep study the whole brain was down 24%, but not evenly. The emotion and memory circuits lost 35 to 41%. The smell areas only 22%. (Its wild sheep was the European mouflon, not the Asiatic one the video drew.)

Rabbits tell it even more plainly. Brain scans of wild and tame rabbits show the tame ones have a smaller amygdala, the fear alarm, and a bigger front part that calms the alarm down. Less panic button, more brake.

Ebinger 1974 · Brusini et al. 2018, PNAS

Let them loose and it can grow back

Farm mink have braincases about a quarter smaller than wild mink. But mink that escaped from Polish fur farms, and have lived wild for less than 50 years, are almost back to full size.

For a long time the textbook said a domesticated brain never recovers. For mink, at least, danger is a gym membership.

Pohle et al. 2023, Royal Society Open Science

Kushim's tablet is real. It is not the one in London.

The Kushim tablet is a palm-sized piece of clay from Uruk. It books about 135,000 litres of barley over 37 months for the temple brewery, and signs off with two signs: KU and SHIM. The name turns up on 18 tablets. It may be a man. It may be his job title. Nobody can tell.

The beer tablet in the British Museum is a different one: daily beer rations for workers, "probably from" Uruk. Its sign for a ration is a head with a bowl at its mouth.

the Kushim tablet, MS 1717, at CDLI · the British Museum tablet · Damerow 2012, Sumerian Beer

Your brain is under construction until about 30

A child's brain has two to three times as many connection points as an adult's, and growing up is mostly cutting them back. Textbooks used to say the cutting was done by the early teens. Counting them in brains from newborn to age 91 showed it goes on through your twenties, in the front part that plans and judges.

The genes that build those connections tell the same story. In chimps and macaques they peak before the first birthday. In humans, at about five years.

Petanjek et al. 2011, PNAS · Liu et al. 2012, Genome Research

The long childhood is as old as your species

Teeth grow in daily layers, like tree rings. A child who died at Jebel Irhoud in Morocco, about 300,000 years ago, was 7.8 years old by that count, and its teeth were right on schedule for a child today. Slow growing-up was already there. Same place, same time as the bully by the river.

Neanderthal children ran a little ahead: their first molar was done about six months sooner.

Smith et al. 2007, PNAS · Richter et al. 2017, Nature · Smith et al. 2010, PNAS

A baby chimp's skull, blown up to adult size

Researchers mapped 41 human and 50 chimp skulls in 3D, from babies to adults. The shape of your adult braincase matches a chimp before it has any adult teeth, just scaled up.

Stephen Jay Gould found the same trick somewhere else. He measured Mickey Mouse over fifty years of cartoons: the eyes went from about a quarter of the head to over 40%, the head swelled, the snout shrank. As Mickey turned from a rascal into a nice guy, Disney's artists drew him younger. Without knowing it, they did to Mickey what the fox farm did to foxes.

Penin, Berge & Baylac 2002, Am. J. Physical Anthropology · Gould, A Biological Homage to Mickey Mouse

Who else plays as a grown-up

Dogs, and the dog researchers call that unusual: adult play is routine in dogs and rare in most mammals. Bonobos, the friendly ape from the face chapter: adults play with other adults more than chimps do. Lab rats: they start play fights more often than wild rats.

And you. The average American gamer is 36. In 2004 it was 29. The players are not being replaced by kids. They are just not stopping.

Bradshaw, Pullen & Rooney 2015 · Palagi 2006 · Himmler et al. 2013 · ESA 2024

Wolf pups meet the world blind and deaf

Wolf and dog pups get their senses at the same ages: smell at two weeks, hearing at four, sight at six. But wolf pups start exploring at two weeks, when all they can do is smell. Dog pups wait until four.

So a wolf meets every new sight and sound as a shock, and a dog meets them as a toy. Add the fox numbers from chapter 1, where fear arrives at 9 weeks and not 6, and domestication looks like one thing: a longer stretch of life when the world is not scary yet.

Lord 2013, Ethology · Trut 1999, American Scientist

1. Were the foxes a fair test?

The farm foxes came from Canadian fur farms and had been bred in cages since the 1890s. Critics say some "new" traits were already there, and that most tame foxes never got the dog looks at all. The fox lab says the point is how much more common the traits became. DEBATED

Lord et al. 2020 · Trut et al. 2020 · chapter 1

2. Why would the traits travel together?

The best idea so far: the neural crest, the embryo cells from chapter 4. They build the face, the pigment cells, the ear cartilage and the adrenal glands that pump stress hormone. Select for calm, you get slightly lazier neural crest cells, and the face, the white patches and the floppy ears come along. Elegant, hard to test, and a 2021 paper is titled, flatly, "no unified explanation for domestication". DEBATED

Wilkins, Wrangham & Fitch 2014, Genetics · Johnsson, Henriksen & Wright 2021 · the reply

3. Did the brain really shrink, and when?

One team says 3,000 years ago, because of writing. Another ran the same skulls and found no drop. Others say bodies shrank and brains followed. And the tame foxes' brains did not shrink at all. STILL ARGUED

chapter 6

4. Who did the breeding?

The video went with executions: the group removes its bullies. The rivals: women choosing gentler men, shared child-raising rewarding patient people, or selection for self-control instead of against temper. They are not exclusive. It could be all of them. DEBATED

chapter 2

5. Is "domestication" even the right word?

A domesticated animal has a master who picks the parents. You did not. Two of the field's careful reviewers point out that almost nobody has measured how fast these human changes happened or how much people varied, so comparing us with farm animals is still more picture than proof. DEBATED

Sánchez-Villagra & van Schaik 2019, Evolutionary Anthropology