By Alex Rosenberg
Medical scientists are too busy dealing with the coronavirus to try to step back and make sense of it. Those of us sequestering ourselves to stay out of their way have the luxury of trying our hands at it. The same indispensable tools science employs to deal with the pandemic will enable us to do so.
How to explain the coronavirus pandemic? How to predict its course? How to mitigate its effects? There is in fact one scientific tool indispensable for doing these things. It’s being used everywhere scientists try to come to grips with these three matters—explanation, prediction, and control. That tool is Darwin’s theory of natural selection. Applied to the past three months data it give us the explanation of the pandemic’s origin, onset and its spread. With the same data it tells us the epidemiology we should expect and how to control it. Employed to guide experiments in the lab, it will help find vaccines to prevent the endless spread of the corona virus. The process Darwin discovered even operates when our immune systems kick in to fight it.
The last three months, and the next several, will be humanity’s most vivid introduction to the power of what Darwin discovered to shape our lives, and the insightfulness of his discovery as a tool of human understanding.
Where did the coronavirus come from? That was pretty easy for molecular evolutionary biology. All that was needed is to combining the process of natural selection with a comparison of the gene-sequences of other viruses with the coronavirus that were living quietly in some bat species. By doing so Chinese scientists were able to trace the way the coronavirus gene-sequence evolved to penetrate human cell walls. The Darwinian process of blind variation and selection started with a gene sequence that couldn’t. Why did it build one that could? Because the process of random tinkering is going on everywhere all the time in the biological domain. It was our dumb luck that the process randomly produced a gene that built a protein that binds onto human and animal cell walls. It only took one. The Darwinian process did the rest. It’s opportunistic as hell.
Why did the coronavirus spread like wildfire? Darwinian insight explains. If the first person infected had died immediately, the corona virus wouldn’t have had a chance to spread. It would have gone extinct along with the person it killed. So it couldn’t have been instantly lethal. But that first coronavirus particle to get inside a human cell was producing inexact copies of itself, some more lethal, some less. This is because, as Darwin discovered, ceaseless blind variation is the nature of the biological realm. The less lethal variants that got transmitted from the first victim would be carried around longer just because the new victims wouldn’t get as sick or die so soon. So the virus particles in these victims had a better chance to jump to still more new victims. In fact, there would be selection for coronavirus particles with random variations that made them longer lived outside of human cells, along with being less debilitating when they did infect a new host, allowing the walking wounded to pass on new copies to others. The coronavirus was being selected for wildfire transmission by the process Darwin discovered. No surprise it managed to do so.
The epidemiology of COVID-19—where it spreads, and the rate of contagion is a matter of mathematical modeling the same Darwinian process. Humans provide the selective environments in which agents of illness—viruses and other pathogens—evolve. The epidemiologist determines their basic reproduction number—how many people one victim on average will infect in a given environment, to accurately predict the pandemic’s course. Darwinian processes are always going to select for infectious disease agents that produce higher basic reproduction numbers.The initial values Chinese scientists have estimated for this reproduction number is almost double the number for the SARS epidemic of 2009. It’s the persistent Darwinian selection of virus particles for larger reproduction numbers that makes isolation, social distance and quarantine indispensable steps in limiting the impact of the coronavirus.
Designing the vaccine itself will be another Darwinian process—random variation among candidates and selective retention of those that kill off the virus particles. That’s how drug design works, not by clairvoyance but by experiments filtering for what works.
And then there is the last Darwinian process—in the human body’s response, the “clonal selection” of the human immune system. The body is constantly producing a vast range of randomly different stem cells that latch on to other cells and destroy them. Almost all these stem cells self-destruct when they bind to the body’s own cells and cell products. But so many randomly different ones are constantly produced that almost always there’s one that will bind to the disease-carrying cell without self-destructing. So it gets to replicate, and every new copy attacks and destroys only the disease carrying cells.
A vaccine works because its molecular structure previews the signature of the disease. It jump-starts still another Darwinian process. The preview starts the screening for the stem cells that will attack the real disease when it comes along.
A famous geneticist once said, “Nothing in biology makes sense except in the light of evolution” . Turns out that includes medicine and public health. But it includes a lot more. We are all living through a half dozen Darwinian processes we can see in action, not just time-lapse CGI animations.
By giving us the explanation of where COVID-19 came from and where it’s going, by deploying the tools to stop it in its tracks and prevent its recurrence, Darwin’s theory vindicates its authority to make sense of the pandemic for us, to tell us what it means.
One thing it tells us forcefully is the fatuousness of a search for a nefarious conspiracy behind the pandemic. Humans don’t have the power to do what natural selection does, operating that fast on so many different levels across the entire world.
For those of us who manage to by-pass the pandemic by staying at home, trying to make sense of it, there is a bigger take-home message. As with every biological processes, making sense of this one doesn’t require transcendent purposes or cosmic meaning. Indeed, it doesn’t even allow them. It’s just nature filtering blind variation for local adaptation, in the way Darwin showed us. Get used to it.
About The Author
Alex Rosenberg is R. Taylor Cole Distinguished Professor of Philosophy at Duke University.