Solving a pre-historic crime wave

How early urbanites controlled violent crime

Image: Cranial traumas show dramatic increase as the first cities were built: Joachim Wahl, University of Tubingen

About 6,000 years ago humans came up with one of their best inventions – the city.  In the city you can re-invent yourself. You can co-create whizzy stuff with others. The marriage market is bigger and you can enjoy interesting food and drink with your date.

In the beginning, these collections of people were a bit rough.  Folk had to put up with weird strangers on a regular basis.

There was no noise control to help deal with the noisy party.  There was tension when young blokes gave the eye to young women from another tribal background. Arguments over the quality and price of fish could escalate.  Joerg Baten and colleagues found that rates of lethal violence went up in early cities (published in Nature Human Behaviour October 2023).

A violent death was one with evidence of head trauma or damage to other bones, such as caused by arrows or spears. Baten and his team surveyed 3,539 skeletons from the Middle East. These people lived from 12,000 years BCE (that’s 14,000 years ago) to 400 BCE. The chart below illustrates how lethal violence skyrocketed as more people moved to the cities.

Violent deaths increased from the lows of the Neolithic / Mesolithic (no more than 10% of all mortality). During the Chalcolithic (also known as the Copper Age and the era of city-states) lethal violence accounted for from 10% to over 25% of deaths.

Image: Joerg Baten et al, Nature Human Behaviour, 2023

But – look a bit further, into the Early and Middle Bronze Ages, and we see that things improved. What restrained out-of-control conflict?

The researchers suggest legal systems were fundamental. Courts became more common during 2,400 – 1,700 BCE (the Middle Bronze to the Late Bronze Ages). Law enforcement through courts provided an alternative to self-help, clan-based, pay-back justice.

The researchers looked at other suspects when accounting for violence.  Did the reduction in violence result from greater social equality? Not at all – inequality increased in cities while violence was relatively low. Palaces and ziggurats (temples) are the physical indicators of an elite doing increasingly well during this time. 

There was no obvious impact of environmental disruption. The proportion of trauma-related deaths was low during the Middle Bronze Age despite agricultural yields declining. Nor did dramatic changes in military capability, such as the spread of cavalry correlate with changes in violent death.

But then, at the end of the Bronze Age, there was a 300-year drought across the Middle East.  Many city-states collapsed. There were large population movements.  The rule of law would have been disrupted. There was another spike in violent deaths from the Late Bronze Age to the new, Iron Age. Cheap iron weapons took a toll.

Over close to 12,000 years of human social evolution violence increased as people congregated in cities. Existing approaches to managing conflict resulted in more violence. Pay-back justice works when clans in conflict can move away to avoid attack and retribution.  In the city the instigators remain close by, pay-back escalates and the death toll goes up.

These early cosmopolitan developed legal (and religious) systems, and the power to enforce those through a centrally controlled army. Rather than local authority, maintained through tribal consensus, there was now a state with divine authority and a monopoly on violence.

A note about mortality rates – these researchers express violent deaths as a per cent of total deaths – skeletons that had clear signs of a violent death vs all skeletons.  Another researcher looking back into prehistory used this methodology – and found that humans had a base rate of around 2% of violent deaths as a proportion of all mortality – pretty much the median level of the Neolithic / Mesolithic lethal mortality that Baten and colleagues found.  According to Our World in Data – in 2019 the global rate of deaths resulting from homicide, wars and terrorism was just under 1% (0.7%, 0.2% and .05% respectively).