In my research focusing on early farmers in Europe, I have often wondered about a curious pattern over time: farmers lived in large densely populated villages, then spread out for centuries and later formed cities again, only to to abandon. Why?
Archaeologists often explain what we call the collapse of cities in terms of climate change, overpopulation, social pressure, or a combination of these. Each probability has been true at different times.
But scientists have added a new hypothesis to the mix: disease. Living closely with animals led to zoonotic diseases that also infected humans. Outbreaks could have led to the abandonment of densely populated settlements, at least until later generations found a way to organize the layout of their settlements to make them more resistant to disease. In a new study, my colleagues and I analyzed the intriguing layouts of later settlements to see how they might have interacted with disease transmission.
Earliest cities: full of people and animals
Çatalhöyük, in modern-day Turkey, is the world’s oldest farming village, dating back more than 9,000 years. Many thousands of people lived in mud houses that were so close together that the residents entered via a ladder through a hatch on the roof. They even buried selected ancestors under the floor of the house. Even though there was plenty of space on the Anatolian Plateau, people sat close together.
For centuries, people in Çatalhöyük herded sheep and cattle, grew barley and made cheese. Evocative paintings of bulls, dancing figures and a volcanic eruption suggest their folk traditions. They kept their well-organized homes tidy, sweeping the floors and keeping storage bins near the kitchen under the hatch so the oven smoke could escape. Staying clean even required them to replaster the interior walls of their home several times a year.
These rich traditions ended around 6000 BC, when Çatalhöyük was mysteriously abandoned. The population dispersed into smaller settlements in the surrounding floodplains and beyond. Other large farming populations in the region were also dispersed and nomadic pastoralism became more widespread. For the population groups that persisted, the mud houses were now separate, unlike the conjoined houses of Çatalhöyük.
Was disease a factor in the abandonment of densely populated settlements around 6000 BCE?
In Çatalhöyük, archaeologists have found human bones, mixed with cattle bones, in burials and waste piles. The crowds of people and animals probably caused zoonotic diseases in Çatalhöyük. Ancient DNA identifies tuberculosis in livestock in the region as early as 8500 BC. and tuberculosis in the bones of human babies not long after. DNA in ancient human remains dates salmonella to as early as 4500 B.C. Assuming that the contagiousness and virulence of Neolithic diseases increased over time, densely populated settlements such as Çatalhöyük may have reached a tipping point where the consequences of disease outweighed the benefits of close living.
A new layout 2000 years later
By 4000 BCE, large urban populations had reappeared, in the mega-settlements of the ancient Trypillia culture, west of the Black Sea. Thousands of people lived in the mega-settlements of Trypillia, such as Nebelivka and Maidanetske, in what is now Ukraine.
If disease was a factor in the spread millennia earlier, how were these mega-settlements possible?
This time the layout was different from the crowded Çatalhöyük: the hundreds of two-storey wooden houses were regularly divided into concentric ovals. They were also clustered in pie-shaped neighborhoods, each with its own large gathering house. The pottery unearthed at the community centers has many different compositions, suggesting that these pots were brought there by different families who came together to share food.
This layout suggests a theory. Whether the people of Nebelivka knew it or not, this lower-density clustered layout could have helped prevent disease outbreaks from consuming the entire settlement.
Archaeologist Simon Carrignon and I tried to test this possibility by adapting computer models from a previous epidemiology project that modeled how social distancing behavior affects the spread of pandemics. To study how a Trypillian settlement would disrupt the spread of disease, we collaborated with cultural evolution scientist Mike O’Brien and with Nebelivka archaeologists: John Chapman, Bisserka Gaydarska and Brian Buchanan.
Simulating socially distanced neighborhoods
To simulate the spread of the disease at Nebelivka, we had to make a few assumptions. First, we assumed that early diseases were spread through food, such as milk or meat. Second, we assumed that people visited other houses in their neighborhood more often than houses outside of them.
Would this clustering of neighborhoods be enough to suppress disease outbreaks? To test the effects of different possible interaction rates, we ran millions of simulations, first on a network to represent clustered neighborhoods. We then ran the simulations again, this time on a virtual layout modeled after actual floor plans, giving houses in each neighborhood a greater chance of interacting with each other.
Based on our simulations, we found that if people did not frequently visit other neighborhoods – about one-fifth to one-tenth as often as other homes in their own neighborhoods – the clustering of homes in Nebelivka would have significantly reduced early foodborne illness outbreaks reduced. This is reasonable considering that each neighborhood had its own gathering house. Overall, the results show how the Trypillian layout could help early farmers coexist in low-density urban populations at a time when zoonotic diseases were on the rise.
The residents of Nebilevka did not have to consciously plan their neighborhood divisions to help their population survive. But perhaps that is true, because the human instinct is to avoid signs of contagious diseases. As with Çatalhöyük, the residents kept their houses clean. And about two-thirds of the houses in Nebelivka were deliberately set on fire at different times. These deliberate periodic burns may have been a tactic to eradicate pests.
New cities and innovations
Some of the early diseases eventually evolved and spread through means other than bad food. Tuberculosis, for example, became airborne at some point. When the bacteria that causes the plague Yersinia pestisbecame adapted to fleas, it could be spread by rats, which do not care about neighborhood boundaries.
Were new disease vectors too much for these old cities? The mega-settlements of Trypillia were abandoned around 3000 BCE. As in Çatalhöyük thousands of years earlier, people spread out into smaller settlements. Some geneticists speculate that Trypillia’s settlements were abandoned about 5,000 years ago due to the origins of plague in the region.
The first cities in Mesopotamia developed around 3500 BCE, while others soon developed in Egypt, the Indus Valley and China. These tens of thousands of cities were filled with specialized craftsmen in different neighborhoods.
This time people in the city centers did not live side by side with cattle or sheep. Cities were the centers of regional trade. Food was imported into the city and stored in large grain silos like those in the Hittite capital Hattusa, which could hold enough grain to feed 20,000 people for a year. Sanitation was supported by public water works, such as canals in Uruk or wells and a large public bath in the Indus city of Mohenjo Daro.
These early cities, along with those in China, Africa and the Americas, formed the foundations of civilization. Their form and function have undoubtedly been shaped by millennia of disease and human responses to it, all the way back to the world’s earliest farming villages.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: R. Alexander Bentley, University of Tennessee
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R. Alexander Bentley does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.