by Daphna Whitmore
It is surprising how rarely the authorities take an evolutionary perspective when dealing with health crises, such as the latest coronavirus spread. They talk about viruses mutating but that is a frequent occurrence, and they treat mutation as though it were equivalent to evolution. A mutation is just the start that generates the variation from which natural selection brings about evolutionary change. Most mutations never amount to anything because they don’t get selected.
Before looking at the environment in which the coronavirus emerged it is worth comparing it to influenza. At the time of writing:
COVID-19 in China: 80,000 cases in a population of 1.4 billion people. 2,239 deaths
COVID-19 in the US: 60 total cases 0 deaths
Outside China: 2,790 cases
By February 15, 2020 Influenza in the US (only):
At least 29,000,000 ill patients
At least 13,000,000 physician visits
At least 280,000 hospitalizations
At least 16,000 deaths, 105 children
Paul Ewald, an evolutionary biologist, explains why the worst influenza epidemic, the pandemic of 1918, was so deadly:
The evidence tells us that the 1918 pandemic was not simply due to the sudden escape of a monstrous mutant into the human population. During the early months of 1918, the influenza was similar to the influenza that has recurred each year since.
But the situation on the Western Front at the end of the First World War was far from normal. There a virus could be transmitted prolifically from people who were entirely incapacitated by infection, as they were slowly moved from overcrowded trenches. Under such unusual conditions, predator-like variants of the influenza virus could exploit the infected without paying the price usually incurred from incapacitation, constantly exposed as they were to new potential hosts. These variants then overwhelmed their milder competitors and spread globally.
Today we do not have trench warfare but we do have animals kept in similar conditions. Science writer and anthropologist Wendy Orent says the emergence of this new virus was predictable, even inevitable. She says:
To understand why requires looking back to an earlier virus that emerged in China, SARS. Like the new illness, SARS was caused by a coronavirus. In 2003, it exploded out of a “wet market” in Guangdon where civet cats, raccoon dogs and multitudes of other animals were caged together in tight, squalid conditions.
Orent has written on such events before and is author of “Plague: The Mysterious Past and Terrifying Future of the World’s Most Dangerous Disease” and “Ticked: The Battle Over Lyme Disease in the South.” She argues that:
The initial victims were all connected to a huge wholesale market in Wuhan, where a thousand stalls housed untold numbers of live animals kept in crowded, filthy conditions. Such “wet markets” are widespread in China, providing a newly-affluent upper class with status-enhancing exotic animals to serve at dinner. Some people also believe that eating wild animals has health benefits.
The problem with the markets is that the unsanitary and tightly packed conditions in which the animals are held create perfect environments for the evolution of viruses that can jump from one species to another. The Chinese government shut down wet markets after the SARS outbreak, but that ban was short-lived.
Orent notes that SARS came from bats originally as appears to be the case with the new coronavirus.
Coronaviruses have proved themselves masters at jumping from one species to another, and how they affect each species can differ greatly. An infection hardly noticeable in a wild animal, perhaps a civet cat, may spread easily to the next cage, whether that cage houses more civets or another mammalian species. With coronaviruses, the jump from species to species appears to happen fairly easily.
The massive poultry farms of Asia, which may house as many as 5 million chickens, present a different but also potentially lethal source of human infection. There, viruses such as influenza become highly adapted and, in crowded circumstances, ever more deadly to chickens, as there is no cost to the virus if it’s lethal — the next host is only a beak away. These virulent avian influenzas can and have killed people. But humans have to catch them directly from the birds. Because they have become so precisely adapted to chickens, the viruses have little potential for human-to-human transmission.
The same evolutionary process can occur on massive pig farms, and can be even more dangerous to people, since people are more like pigs than like chickens. The deadly 2009 swine flu pandemic sprang out of one such massive pig farm in Veracruz, Mexico, where hundreds of pigs died in an outbreak that eventually moved into people.
The environment of “wet markets” creates the right environment for virulent diseases to be selected for amongst the animals and then spread to humans:
With SARS, as well as the new coronavirus, it appears that the virus jumped first to the people working with these animals in the market, and then began another process of evolution, which allowed it to spread from human to human, adapting to its new host species and becoming more effective at that adaptation all the time. As a result of such evolution, we get brand-new human diseases like 2019-nCoV, which did not exist only months ago.
Orent stresses we need to learn the right lesson from this outbreak:
If we want to forestall the evolution of ever-newer, and possibly deadlier, human-adapted viruses, live animal markets must be permanently shut down. Until the Chinese government outlaws these markets, until factory farms housing millions of animals are eliminated, until we take the inevitable logic of disease evolution into account, novel, and potentially deadly, human diseases will continue to arise. Again. And again. And again.
As well as stopping/preventing these virulent new diseases Orent rightly points out that panic and overreaction are not helpful. She reminds us: “80,000 people died of flu last year in the US alone, and there have been 16,000 so far this year. No one is happy about Covid. But please keep things in perspective.”