For an epidemic to take place, we now know better than ever, it takes, above all, one basic characteristic: that we are very close to each other. That there is little safety distance. That there is, in a way, a tendency to overcrowding.
For that reason, epidemics are relatively recent. Something that was born as a result of the development of agriculture. Because it was agriculture that pushed us to live ever closer to each other .
Calories and overcrowding
Farmers had more food, they could unite into larger clans, establish settlements, reproduce, cooperate … All of that is very good, and they are some of the powerful reasons why agriculture did not disappear. However, there was an almost invisible tribute that all the farmers were paying .
As there are more calories, there are more people, one should not travel so much to look for food, but one was also forced to be subject to a piece of land (the one that was cultivating). The more people in less space, the more crowded. And the more crowded, the greater the number of infectious diseases .
If the population density of hunter-gatherers was below one individual per square kilometer, that of farmers was up to ten individuals per square kilometer in simple agrarian economies, and above fifty individuals per square kilometer in villages. larger, as Zimmerman, Hilpert and Wendt have estimated in a study published in Human Biology in 2009.
But it was not only overcrowding that spread infectious diseases better, but trade, fueled by the surplus food provided by agriculture . By exchanging goods with others, microbes are also exchanged, ushering in an era of epidemics of tuberculosis, leprosy, syphilis, plague, smallpox or flu.
Many of these diseases, such as malaria, already existed, but in a very low proportion. The word epidemic just didn’t make sense before the Neolithic .
Other secondary effects of agriculture, and overcrowding, were: accumulation of waste (ideal breeding ground for microbes and transmitters such as rats), stagnant water from irrigation canals, and continuous contact with domesticated animals. In total, more than one hundred infectious diseases caused or aggravated by the origin of agriculture .