Image: Egyptian domestication of wheat and cattle - 3,400 years ago; wikipedia.org
Humans are good at domesticating plants and animals. Supplies of rice and other cereal food crops (corn, wheat, barley) led to well-fed and increasingly large settlements and cities.
Dogs have been domesticated since the last Ice Age (around 14,000 years ago). They contributed to hunting success and later to the herding of other domestic animals, and they remain the ultimate bestie and bed warmer.
The last big domestication was when people climbed onto horses – about 4,000 years ago – with profound effects on long-range mobility and warfare.
Humans are impressive in their domestication of other animals. But their biggest domestication achievement has been their self-domestication.
Charles Darwin recognised that domestication produced a suite of physical, physiological and behavioural changes. The “domestication syndrome” (or DS) includes (Adam Wilkins and colleagues):
“increased docility and tameness, coat color changes, reductions in tooth size, changes in craniofacial morphology, alterations in ear and tail form (e.g., floppy ears), more frequent and nonseasonal estrus cycles, alterations in adrenocorticotropic hormone levels, changed concentrations of several neurotransmitters, prolongations in juvenile behavior, and reductions in both total brain size and of particular brain regions.”
Dmitri Belyaev, Lyudmila Trut and their colleagues began a remarkable experiment back in 1950s Russia. Working with silver foxes from fur farms Belyaev deliberately bred foxes for tameness. When his research assistants put their (gloved) hand into their cage – did the fox react violently, or did they tolerate, even approach the outstretched hand?
The researchers bred from the tamest 10% in each generation. Successive generations of foxes were increasingly tame. After 40 generations, they wagged their tails as humans approached, licked rather than bit hands and whined when people left. Remarkably they also demonstrated physical changes – evidence of the DS. Their ears went from upright to floppy. Tails became curly. Their coats became spotty. Their snouts became blunter.
Image: The silver fox domestication experiment, Lee Ann Dugatkin; evolution-outreach.biomedcentral.com
Over a much longer time, humans show similar changes. Human faces became flatter, teeth smaller. Women developed a regular estrus cycle. Childhood lasted longer. However, humans have a notable exception to the usual DS suite of physical change.
Image: hominids; smithstonianmag.com
The domestication syndrome typically results in smaller brains. But human brains have got bigger, especially the wrinkly cortex on top.
This difference reflects the diverging paths of humans and their domesticates.
Domestic animals have less to think about. Their reproduction is managed. There is none of the complicated competition for mates that their ancestors had to deal with. Their needs for food and water are sorted, and the risk of predation is minimised. These are the short-term advantages of being on the human menu.
The path to domestication appears to be the selection for tameness. From wild wolves to obedient dogs, freedom-loving steppe-mustangs to docile beasts of burden. Aggressive foxes to cute and friendly foxes. As humans lived and worked together increasingly niceness would have facilitated the human super-power of collaboration.
Humans evolved in an increasingly technical world. That has resulted in an upward spiral of learning – from flaking stone tools to curating online profiles.
Collaboration helped that learning. Before our hominid ancestors had language learning was small-scale. The novice stone knapper watched the master.
Language scaled up learning opportunities.
Through oral and then written traditions the wisdom of ancestors and the ever-extending community kept multiplying.
It wasn’t just technology that encouraged bigger brains. Social life demands brainpower. Will Jo do what they said they will? Who do you owe favours to? Who is indebted to you? That’s the easy stuff. What about, who is indebted to Big Jim? Who has benefitted from the generosity of Friendly Sue? And all this can go back generations. This is a lot to keep tabs on. You need a quality memory and reasoning device to get that sorted.
Humans gained increasing benefits through getting along. Childcare was shared across the village. Communities made music together (perhaps originally to scare away nocturnal predators, then because of the rewards of being in synch with others). Goods were traded across increasing distances.
Collaboration is based on trust. Trust is easier with people who speak the same language, share the same religion and beliefs about what is good and bad, right and wrong
It’s intriguing that humans tend to see their gang as civilised, while the other kind have worse manners, are less moral, and act like wild savages. Those others are not nice! In the 14th century, a Chinese writer described the natives of islands “beyond the sea of China..They live on raw food. When caught and fed on food with fire it purges them daily…During this treatment many die but if they do not they may be reared and become able to understand human speech.” By which the writer P’ing-chou-k’o-t’an meant to understand Chinese.[1]
This small but not unusual example of the enslaving of humans as if they were another species to be oppressed and exploited illustrates the human ability to dehumanise those who look or sound different.
This fits with the evidence that we are capable of inflicting terrible violence on others. Particularly if we see them as sub-human. Humans, chimpanzees and bonobos split from our common ancestor some time ago (it could be as few as 5 million years ago, as many as 13 million years).
We share 98.7% of our DNA with both chimps and bonobos. But we have quite different repertoires of violent behaviour.
Humans share chimps’ proactive, targeted and planned aggression. Human similarities with chimps’ proactive aggression include patrolling borders, ambushes and torture. But we don't see (or not often) the “amok” rampaging, reactive aggression displayed by male chimps.
Humans are like bonobos in being less emotionally reactive and violent, but unlike the bonobos humans are capable of deliberate violence.
How did human self-domestication happen? And how did it result in this divergent inclination to violence? Richard Wrangham has suggested that humans selected out the reactively aggressive individuals the same way Dr Belyaev selected out aggressive foxes. The aggressive foxes became fox fur coats. Wrangham suggests that bullies were killed or banished.
There is an alternative evolutionary mechanism to this brutal selection method. Darwin introduced the theory of sexual selection in his 1871 book The Descent of Man. If females are selective when choosing a mate their choice will influence the characteristics of the next generation. And of course, they are. Women would likely have chosen to partner up with nice guys. Meaning increasingly nice children and humans.
If you are a mother-to-be you are looking for someone who will help with child care, provide food for you and the baby, and proactively direct their aggression towards the savages on the other side of the hill. Singing ability would have helped too.
Looking at the DNA of people from 51 different populations researchers Sebastian Lippold and eight colleagues found evidence that over the eons women were more likely to move between populations. And that men and women had very different reproductive success. They estimate that as modern humans were moving out of Africa to Europe 45,000 years ago women outnumbered men 100:30 in reproductive success. Back in time, only a relatively small proportion of males got to be dads, while the great majority of females became mums. Their choices would have been a significant driver of human evolution.
Some of the men who missed out would have been victims of inter-tribal fighting and high-risk hunting. Some would not have measured up to the standard of what a woman wanted in a man. This is a recipe for decreasing reactive aggression as women chose tamer men.
Humans evolved big brains during their self-domestication. They have recently (in evolutionary terms) used that reasoning power to develop local and cross-national approaches to ensuring the rule of law. There is some evidence (in the short term) of that reducing human violence.
[1] Quoted from P 258 of Peter Walker (2024), Hard by the Cloud House