Starting in February 2021, each month we shine a light on an aspect of science that is often misunderstood or misrepresented. Read all our Misconception of the Month articles.
Fact: Evolution happens because some variants are more successful than others.
Misconception: Evolution happens in response to the needs or efforts of individuals.
Why it matters: If we want to predict or influence how species will change over time, it’s more helpful to focus on the conditions that favor or discourage the changes we care about, and not on what changes organisms “need” or what they “are trying to do” to survive.
New variants of the virus that causes COVID-19 are all over the news right now. The way the variants are often discussed reinforces one of the most pervasive misconceptions about evolution: that it occurs in response to what organisms want or need.
Every high school biology teacher has heard a student say: “Polar bears became white so they could hide in the snow.” And those teachers have had to explain (year after year after year after year): “Polar bears are white because white bears are better camouflaged and therefore more likely to survive and have more white baby bears. That’s how the trait of white fur (which some bears already had!) became widespread.” Or I guess they could just take a shortcut and say: “Polar bears are white because the brown ones are dead.” Cruel, but fair. (If you really want to geek out on polar bear adaptation, here you go. You’re welcome.)
It’s easy to see how this misconception takes root. All the organisms we see around us have — obviously — evolved the characteristics they need to survive in their environments. It’s a small step then to think that these characteristics evolved in response to their needs. But the thought that new characteristics evolved because organisms needed them only seems plausible because we can’t see all the organisms that didn’t survive because they didn’t evolve the necessary characteristics. (Maybe they just didn’t want them badly enough?)
The better way to think about evolution is that it’s a process by which the unsuccessful organisms are weeded out, leaving behind the ones that already had the traits needed to survive under current conditions. It’s not so much that evolution identifies the great but that it rewards the adequate. If evolution were a sporting event, all surviving organisms would get a participation trophy, not a gold medal.
Public health implications
This has practical implications. For example, in public health, our interventions should focus on minimizing the conditions that favor variants with traits we don’t want, like new strains that are resistant to existing treatments, or invisible to the antibodies generated by vaccines, or more transmissible, or that cause more serious disease. But almost always, evolution is described more like this:
If a virus wants to escape the human immune system, it doesn’t want to mutate itself so that it dies or can’t replicate….It wants to preserve fitness but disguise itself enough so that it’s undetectable by the human immune system.
When we think about evolution in terms of viruses “wanting” to escape the immune system or “wanting” to spread more easily, we lose sight of the fact that there’s no agency involved on the part of the virus. It may be handy to talk about viruses as cunning agents bent on maximizing their reproductive success by hook or by crook, but it fundamentally misrepresents how evolution happens: viruses don’t specifically generate the mutations they need or want, they just mutate. Then evolution favors the mutations that work.
Also, not to belabor the point, but there’s no “Team Coronavirus” bat cave where a virus mastermind is coordinating the tactics of every individual virus particle. Just a bunch of individual viruses, each invading some human cell in some human somewhere and commandeering the cellular machinery to make a bunch of imperfect copies of themselves.
Nevertheless, the temptation to describe viruses as entities with intentions seems to be overwhelming. Here are a couple more examples of news coverage that reinforce this misconception that viruses “want” things:
For example, if I had COVID-19 and you got the vaccine and had developed antibody protection, then I can’t give it to you. The virus wants to get into you but it can’t, so it tries to go to the next person and the next and if there’s not enough people for it to pass to, coronavirus goes away from a pandemic outbreak level. (Alabama Newscenter)
“That’s what a virus wants,” said Dr. Jim Wright, the facility’s medical director. “A number of people with multiple illnesses, living very closely. Viruses love that.” (The New York Times)
So if they can’t will themselves into existence, where do these new variants come from? Well, every single viral infection begins with a cloud of viruses that are all slightly different from one another and each infection produces a new cloud of non-identical new viruses (often called progeny). Some viruses have a very high mutation rate, so much so that lots of the progeny aren’t even functional any more. Influenza, for example, generates huge diversity with every round of infection with lots of the progeny defective in some way. But that’s not true of all viruses. Every existing viral species has, over evolutionary time, arrived at a level of mutation that has proven successful at balancing the need to change over time against changing so much that too many viral progeny are dysfunctional. Think of it like an automaker that has to trade off how much money it spends to make its cars reliable versus how consumer needs will change in the future: if you build a car that never needs repair but doesn’t have any cup holders, the next generation of consumers might not buy it no matter how popular it is now.
Okay, maybe that’s not a perfect analogy, but you get the picture. The important thing is that the viruses that we see causing disease are the ones that succeeded at that balancing act. Viruses that were unable to generate enough variation to survive changes are gone. So are viruses that mutated so fast that their progeny couldn’t infect the next host. What’s left are the “goldilocks” viral species with a mutation rate that just … works.
Mutations happen. The Environment Selects.
You may have heard that the new coronavirus — SARS-CoV-2 — has a relatively low mutation rate. That means that in any given infection, the cloud of viruses that started the infection is more uniform than it would be with a virus like influenza, and the cloud of viruses generated in each individual infection is also more uniform. Why does that matter? Because evolution of a species can only build on the variation that’s already present, and in the case of coronavirus, variation is relatively limited.
The amount of variation is one side of the evolutionary story. The other side, of course, is the external environment. If the existing cloud of viruses (which, again, in the case of the coronavirus, is relatively uniform) faces an unchanging external environment (say, one in which almost no one is immune), there is no pressure for any particular variant to become more common.
Sort of like, if everyone is perfectly happy watching Days of Our Lives, there’s no need to invent reality TV.
Okay, another imperfect analogy.