The conspiracy theory asserting that the virus linked to COVID-19 was crafted in a laboratory to spread worldwide death and panic is among the most tenacious in circulation.

In a survey of 3,000 Americans, one in four said they believe the virus might be a bioweapon developed by a government or terrorists. Speculation has been widespread enough to be addressed by a team of scientists in the U.S., U.K. and Australia, which concluded in a Nature Medicine article that “SARS-CoV-2 is not a laboratory construct or a purposefully manipulated virus.” 

The idea of the virus being a human creation made Maciej Boni—an associate professor of biology at Penn State University who studies where diseases come from and how they evolve—laugh.

“There is no indication of that,” he said.

How do the vast majority of scientists across the globe know that the new coronavirus came from a natural source? 

Several pieces of evidence show that the virus is not a lab product:

  • Researchers have found that the virus circulated in bats and other animals and then jumped to humans.
  • Some parts of the new virus could have evolved from ancient viruses, say scientists who  have traced its genes to known, naturally occurring viruses. 
  • And then there’s the simple fact that creating a deadly virus is almost impossibly difficult.

Finding the entry key

The scientists who reported their findings in the March 17 Nature Medicine piece examined a part of the virus known as the receptor-binding domain. This structure, which exists in other well-studied viruses that infect humans, is the part of a virus that hooks onto a cell within an animal in order to enter it. 

Comparing the receptor-binding domains of different viruses allows scientists to understand how a virus does its damage and how it evolves. Mutations in viruses are not uncommon, and natural selection helps them infect humans more efficiently. 

You can think of the receptor-binding domain as a key. If it fits the keyhole of a human cell wall, the virus can enter. 

Coronaviruses have had plenty of time to evolve and try different keys in different animals. Scientists have long warned of this kind of threat. The new coronavirus is able to enter human lung cells because it has tried so many keys that it eventually found the one that fits.

Cross-species infections

The process of a virus jumping from one animal to another has been studied in the lab. Typically, researchers grow a virus in cells from an animal such as a bat. Then they take parts of this virus and put them in a new type of cell, such as one from a chicken. 

If the virus infects the chicken cells, that means that it has modified its key to open a different door—the cells of another kind of animal. Viruses do this naturally, jumping from one animal to another. 

Viruses can pass naturally from animals to humans, Boni said, in a process called a zoonotic transfer. The H5N1 virus that causes avian influenza, or bird flu, is but one example. For now, we’re not sure when and how it happened, but we know that SARS-CoV-2 made the same jump.

As a virus morphs, it can mold itself to become more deadly. To understand its origins, researchers look at its blueprint: the genetic material packaged within a virus’s membrane.

Sequencing the genes

Chinese scientists have decoded the genome of SARS-CoV-2 and made the data available. Almost every segment of the virus can be traced back to ones that had been circulating in bats or pangolins. This is how scientists know where it came from, Boni said.

If scientists were to have engineered SARS-CoV-2, the result would have been a patchwork genome. They would have had to start with a backbone and add parts to it from here and there.

The result would have looked like a pair of jeans with random bits of silk and satin stitched on. Scientists would recognize human handiwork, because the seams and odd juxtapositions would be evident. But that is not the case with this virus. 

“The genetic data irrefutably show that SARS-CoV-2 is not derived from any previously used virus backbone,” the Nature Medicine authors wrote.

Is it possible that the stitching was so well done that scientists didn’t notice the cuts?

Andreas Stürmer, an independent biologist who studied biotechnology and environmental engineering at the University of Applied Sciences in Austria, said it’s not very likely: “To engineer a virus and make it deadly is really difficult.”

Hundreds of scientists would need to work for a decade or more trying to come up with such a virus in the lab. 

“It’s not efficient to try out all the different mutations and combinations of mutations, millions and trillions,” Stürmer said, “just to find the one that would work.”