How agriculture became our killer

Georgina Holmes explores how the adoption of agriculture came at a cost to our health

The transition from hunting and gathering to farming led to a rise in disease prevalence and led to population collapse

11,500 years ago (at the end of the last ice age)^* humanity made one of its greatest leaps in innovation: agriculture. Previously hunter-gatherers, bands of early Homo Sapiens gradually adopted the practice of domesticating crops over thousands of years. Completely independently, peoples across the world adopted agriculture at vastly different times – the latest being the Australian aborigines, who were still hunter-gatherers when the first imperial soldiers arrived in the 19^th century – but it’s origins lie in the Fertile Crescent of the Middle East. It is likely that the change in climate when the ice age ended, and the communities that had grown to survive in the cold climate, were key factors in driving trials in agriculture. 

By around 6,000 BC many communities were dependent upon farming. What did this mean for humanity? Mobile hunter-gatherers became sedentary communities; civilisations and innovations began to grow; status and social stratification arose from the increase in free time; but most of all our health declined rapidly.  

Disease did inevitably affect hunter-gatherers for millions of years. However, the origins of major infectious diseases are thought to have only plausibly originated from the rise of agriculture. 

Agriculture came with a trade-off: increased fertility and population growth. Nevertheless, this benefit to growing civilisations perpetuated the spread of disease. In Polynesia, intensive agricultural islands had population densities exceeding 120 per square mile – this was a catalyst for the transmission of diseases and decline in sanitation. Air, water and reproductive-borne diseases found humans the hotspot for transmission. Microbes that cause gastroenteritis, for example, spread from faecal contamination of food and water whilst gut rotaviruses kill lining cells, making for raw areas which can neither absorb nor retain fluids causing diarrhoea. With each gram of faeces containing 109 viruses, microbes could thrive in such settled and confined communities with poor sanitation – people were living amongst their waste and ill, unlike nomads. Crowd-diseases could not be sustained with the sparse and mobile bands of hunter-gatherers, and so it was only when agriculture allowed people to settle and cheat death that we see a rise in infectious disease. 

Equally, the growth in the successful reproductive turnover of humans was a hotspot for diseases. Evolution selects for organisms most effective at reproducing, allowing for the fast and widespread infection of new hosts by a microbe. Hence, densely knit, sedentary and ever-growing human populations where the prime opportunity for microbe evolution.  

Zoonotic diseases have become infamous in light of the SARS-CoV-2 outbreak, but animal to human transmission is where infectious diseases really began. Ironically, microbes behind our own epidemics are most commonly confined to humans. Yet, the infectious killers throughout human history – smallpox, flu, TB, malaria, plague, measles etc. – all evolved from diseases in animals.  

Domestication of animals meant humans were living in close proximity to their livestock, and social animals such as cattle were also confined to spread disease more readily. Cows and pigs, social animals as stated, were already plagued by epidemic diseases and so our domestication of them allowed for transmission of non-human disease to us. This is one reason why the Americas, before its ‘rediscovery’, had significantly fewer diseases than Eurasia and why the Inca died from Spanish germs – 80% of their large domesticable animals were hunted to extinction or died at the end of the last ice age. As a result, only five animals were domesticated. The relationship between the prevalence of disease and number of domesticated animals strongly suggests that pastoral agriculture played a crucial role in the rise of infectious diseases. 

Diamond J. (1997). Guns, Germs, and Steel: the Fates of Human Societies. Norton; New York. 

Arguably, hunters had a short life-expectancy and those that fell ill could not be supported due to the mobile nature of the lifestyle (as the archaeology suggests, the infirm were abandoned). As a result, there would be less time to develop susceptibility to infection and those who fell ill could not pass the disease on. This does not demonstrate that it is hard to explore the infectious disease of nomads, although it is, but rather that agriculture provided a vulnerability that meant diseases were more widespread and could be sustained. 

How did agricultural diseases become our killers? The Indian population of Hispaniola was around 8 million in 1492 AD, after Columbus’ arrival the population was non-existent, zero by 1535. Examples like this are found across the world – everywhere European peoples went with their infectious diseases, populations were crippled. Infectious disease arose in dense areas by means of agriculture, and killed, and they spread in dense areas not exposed to agriculture, and killed.  

Disease is just one area which agriculture paved the way to in the decline in human health. There are many other aspects of crop production which led to the ills that we face today. From nutritional deficiencies causing decreased stature and robusticity to softer foods increasing malocclusion, there is a plethora of areas of health which suffered as a result of agriculture.  

*Some believe that the seeds of agriculture were actually sown as far back as 23,000 years ago. But for the sake of a concise article I will use the widely accepted date of 12,000 years ago.