This article from Aeon argues that we shouldn’t worry so much about some random mutation of an animal virus coming out of the jungle and destroying us. Instead, it is the conditions in human society that allow new diseases to evolve and adapt to us that we should be more concerned about.
According to this argument, new germs that erupt into our species will be potential triggers for pandemics, while germs that have a long history in a host species will have evolved to be relatively benign.
Many health experts take the notion further, contending that any coming plague will come from human intrusion into the natural world. One risk, they suggest, comes when hungry people in Africa and elsewhere forge deep into forests and jungles to hunt ‘bushmeat’ – rodents, rabbits, monkeys, apes – with exposure to dangerous pathogens the unhappy result. Those pathogens move silently among wild animals, but can also explode with terrifying ferocity among people when humans venture where they shouldn’t. According to the same line of thought, another proposed risk would result when birds spread a new pandemic strain to chickens in factory farms and, ultimately, to us.
But there’s something in these scenarios that’s not entirely logical. There is nothing new in the intimate contact between animals and people. Our hominid ancestors lived on wildlife before we ever evolved into Homo sapiens: that’s why anthropologists call them hunter-gatherers, a term that still applies to some modern peoples, including bushmeat hunters in West Africa. After domesticating animals, we lived close beside them, keeping cows, pigs and chickens in farmyards and even within households for thousands of years. Pandemics arise out of more than mere contact between human beings and animals: from an evolutionary point of view, there is a missing step between animal pathogen and human pandemic that’s been almost completely overlooked in these terrifying but entirely speculative ideas.
According to the evolutionary epidemiologist Paul W Ewald of the University of Louisville, the most dangerous infectious diseases are almost always not animal diseases freshly broken into the human species, but diseases adapted to humanity over time: smallpox, malaria, tuberculosis, leprosy, typhus, yellow fever, polio. In order to adapt to the human species, a germ needs to cycle among people – from person to person to person. In each iteration, the strains best adapted to transmission will be the ones that spread. So natural selection will push circulating strains towards more and more effective transmission, and therefore towards increasing adaptation to human hosts. This process necessarily takes place among people.
It goes on to talk about some major plagues in history, including the 1918 influenza which is “the rod by which all other pandemics are measured”.
We could take some comfort in all this – the diseases that cause the most suffering are the ones that evolve within and amongst people, suggesting that there should always be sub-groups of people who develop immunity to them. This suggests that despite terrible suffering, they shouldn’t represent an existential threat to the species. There is a plague in history that I find even more horrifying that 1918 or the Black Death, and that is the almost complete ravaging of Native American populations after 1492. That was a case of diseases that evolved in and amongst human populations, that were then unleashed on another isolated population (possibly a very large one) that had no resistance to them. So as much as we worry about international travel spreading germs, maybe it means it would be harder for some germ to completely sneak up on us, since there are virtually no human populations that are truly isolated anymore.
There is still the worst possible scenario though – somebody taking one of the ugly human-adapted diseases mentioned in this article, and purposely modifying it into something that the population has no immunity to.