Behind every pandemic is a tale of its murky origin.

When HIV/AIDS emerged in the 1980s, it was alleged, with a little Soviet help, that the virus had been developed in an American lab. Between Washington’s inaction on the epidemic and its sordid past of shady experiments, proponents said the theory couldn’t be dismissed out of hand.

After many early cases of tick-borne Lyme disease were first identified around Long Island Sound, it was deemed too much of a coincidence that the U.S. military’s Plum Island animal research lab sat on an island in the sound itself.

When SARS emerged in 2003, so did fears of the severe acute respiratory syndrome’s unnatural origin. “It’s a very unusual outbreak,” bioweapons expert Ken Alibek told the New York Times at the time. “It’s hard to say whether it’s deliberate or natural.” One Russian scientist posited that “the propagation of the atypical pneumonia may well be caused by a leak of a combat virus grown in Asian bacteriological weapons labs.”

And in recent years, efforts to eradicate Ebola have been hobbled by attacks on health care workers motivated, at least in part, by a belief that the virus is man-made.

Blaming humans for disease is as old as time itself.

Blaming humans for disease is as old as time itself. It’s inherently hard to trace outbreaks that take tangled paths from their origin point to where they’re first detected. Without firm answers, humankind loves to invent stories, from the Black Death of the 14th century to the 2009 H1N1 outbreak. In the absence of certainty, both sets of theories—natural or man-made—seem plausible: like Schrödinger’s cat, for virology.

When infectious diseases can be explained, however, nature is almost always the culprit. After SARS emerged, scientists suspected that the coronavirus had jumped from a bat to another mammal—probably the masked palm civet—but couldn’t explain how it had appeared on a farm in Foshan, in China’s Guangdong province.

More than a decade after the outbreak, researchers from the Wuhan Institute of Virology discovered something interesting: Villagers who lived near bat-ridden caves in Yunnan province, around 900 miles from where the first outbreaks were recorded, had high levels of SARS antibodies, despite having never been infected. While it is next to impossible to figure out exactly how SARS traveled that distance, scientists are now fairly sure the journey began in that cave before passing to a mammal that ultimately infected a person.

Bats likely played a crucial role in incubating Ebola as well. A very similar strain of HIV to the ones seen in humans was discovered in chimpanzees in 1999, although it’s still unclear when exactly it jumped to humans. It’s still uncertain where Ebola or Lyme disease truly came from—and we may never know. But what we do know is that they almost certainly did not come from a U.S. government lab.

But, of course, sometimes governments do experiment on unwitting civilians. Sometimes viruses do escape from labs.

Yet although lab spillovers do happen, the vast majority are rapidly contained. Instances of serious outbreaks caused by malice or incompetence are vanishingly rare. One of the only known examples dates back to 1977, when a previously eliminated strain of H1N1 reemerged, likely as the result of a Soviet live vaccine program gone awry.

Given that history, it was no surprise that theories around COVID-19’s supposed lab origins emerged. But this time around, it’s not just idle speculation. It’s being taken as a serious possibility by some of the highest levels of the U.S. government—and by media keen for a new narrative.

When COVID-19 was first detected in December 2019, the Chinese government responded in its usual fashion: with repression and secrecy. Weeks of cover-up suddenly switched to countrywide containment. The ham-fisted attempt at secrecy raised the question: What else were they hiding?

It didn’t take long for online sleuths to hold up a compelling piece of evidence: The Wuhan Institute of Virology, the same one that had helped identify the likely origin of SARS, was just about 9 miles from the first reported outbreak.

In January 2020, the theory began on the fringes, with allegations of a secretive bioweapons program. Within weeks, the theory had broken loose on a network of shady and disreputable websites armed with little more than questions and supposition. The mainstream media’s silence, they said, was evidence of their complicity. They latched on to crumbs of evidence emerging in the early bedlam of the global pandemic, like a paper, later withdrawn, suggesting HIV genes had been inserted in the virus.

Then, the theory found a powerful constituent. Fox News reported in April 2020 of “increasing confidence” in the U.S. intelligence community around the idea that the virus came from the Wuhan lab—maybe not as a biological weapon, but as the result of an accidental leak. Then-President Donald Trump, in response to the news network, coyly endorsed the theory.

By that May, Secretary of State Mike Pompeo was promising “conclusive” evidence to back up the hypothesis.

That conclusive evidence didn’t materialize: Instead, there were dodgy dossiers and yet more sources talking up an “agreement” among “most of” America’s 17 intelligence agencies around the lab leak theory. (The Times would later report that then-Deputy National Security Advisor Matthew Pottinger had endorsed the lab leak theory early on and had been pressing intelligence agencies to back him up.)

The possibility of a routine lab accident became caught up in the theories about bioweapons and germ warfare.

But while the theory was reported, many media outlets also dismissed it as conspiracy mongering. The possibility of a routine lab accident became caught up in the theories about bioweapons and germ warfare. Scientists were keen to focus debate on how to deal with the pandemic, not a geopolitical fracas.

Some circumstantial evidence emerged to support the theory, such as State Department cables reporting security issues at the Wuhan lab from 2018—although the full cable was less dramatic than the headlines about it. Big claims by the proponents didn’t pan out, however. Not one other country from the Five Eyes intelligence community backed up the claim that certainty was mounting—Australia even contradicted it outright, as did other parts of the U.S. intelligence community.

But as the Trump administration was collapsing, its former members saw pushing the theory as a path to future credibility.

In late December 2020, Pottinger popped up again in the British press, after telling Conservative members of Parliament that “ there is a growing body of evidence that the lab is likely the most credible source of the virus. ” One Tory MP reported Pottinger had said a Chinese whistleblower was providing the U.S. government with evidence for the theory.

A “fact sheet” from Pompeo’s State Department from around that time was simultaneously more ambiguous than Pompeo had been, acknowledging that it was indeterminate whether the virus’s origins were natural or accidental, and more conclusive, reporting that “several researchers inside the [Wuhan Institute of Virology] became sick in autumn 2019, before the first identified case of the outbreak, with symptoms consistent with both COVID-19 and common seasonal illnesses.”

Then came the speculation.

This January, the novelist Nicholson Baker took to New York magazine to proffer his conclusion: “SARS-2 was not designed as a biological weapon. But it was, I think, designed.”

Baker offered an incredibly detailed, but speculative, theory. It goes like this: In 2012, workers in a copper mine in Mojiang, in Yunnan province, contracted a then-unknown illness from bat droppings. Samples of the virus—particularly one novel virus they named RaTG13—were transported back to Wuhan, where it was experimented on, including alterations to its spike proteins. And then, Baker wrote, the virus may have just “got out.”

In May, the Bulletin of the Atomic Scientists joined the fray, with a piece from Nicholas Wade, a former New York Times correspondent with a dubious line in racial theories, running with Baker’s hypothesis.

He noted, correctly, that many of the coronaviruses—like those that cause COVID-19 and SARS—originate in the caves of Yunnan province. If it were natural, he contended, why would the outbreak occur nearly 1,000 miles away? “The bats’ range is 50 kilometers, so it’s unlikely that any made it to Wuhan,” he wrote.

On the biology of the virus itself, he wrote that the furin cleavage site—a tiny enzyme on the virus that makes the coronavirus as ruthlessly effective at infecting humans—is a clue as to the virus’s lab origins. Baker noted that there are two ways in which this cleavage site could be attached to the virus naturally: by mutation of the virus itself or by fusing with another coronavirus through a process called recombination.

The theories put forward do latch on to elements of truth: Chinese infectious disease research is secretive and riskier than it ought to be.

Wade, even after quoting a virologist who insisted that “recombination is naturally very, very frequent in these viruses,” concluded that both explanations are unlikely. Instead, Wade wrote: “That leaves a gain-of-function experiment.”

“Gain-of-function” is a phrase that has gotten plenty of airtime in recent weeks. The process, generally speaking, involves forcing a virus to evolve and mutate in a lab, mimicking but intensifying the conditions it may face in the real world, largely in order to understand how such mutation takes place in the wild. The practice is risky, but not forbidden: The United States also conducts these sorts of experiments.

The theories put forward by Baker, Wade, and others are enormously complicated, and they do latch on to elements of truth: Chinese infectious disease research is secretive and riskier than it ought to be. The Wuhan lab did find a coronavirus it called RaTG13. Workers in Mojiang did fall ill in 2012 with a mysterious pneumonia, prompting researchers at the Wuhan lab to more intensely study the viruses hidden in those caves, as they told foreign reporters.

Beyond those crumbs of truth, however, everything is just speculation.

The floodgates opened on the theory. The Wall Street Journal recycled the report about the ill Wuhan lab workers. New York magazine condemned the dismissal and smears from the “liberal media” of the theory’s boosters. Sen. Tom Cotton, an early supporter of the theory that the virus came from a lab and may have military origins, has taken a victory lap over his apparent vindication. Sen. Rand Paul dragged the gain-of-function theory into hearings on COVID-19, alleging that the United States helped fund those experiments. The skepticism and debunking, pundit Matthew Yglesias wrote, has amounted to the “media’s lab leak fiasco.”

On May 26, President Joe Biden ordered his advisors to “redouble” their efforts to find information about the origin of the virus. At the G-7 summit, a joint statement called for further investigation, while Biden said the virus could have been “an experiment gone awry.”

From the outside looking in, it seems the balance of probabilities has shifted. Where once, in early 2020, the overwhelming preponderance of evidence pointed toward COVID-19 being of natural origin, now the lab leak theory is gaining steam.

But it’s a mirage. Despite proclamations to the contrary, there has been scant new, hard evidence pointing to the lab leak theory. What we have are the same conclusions drawn from China’s malign incompetence, the same pieces of circumstantial evidence, and a speculative theory.

None of this means a lab leak is impossible. But the “growing evidence” simply isn’t there.

“I don’t think that we’ve learned anything new in the last few months,” said Stephen Goldstein, who studies evolutionary virology at the University of Utah.

“We’re completely in want of evidence.”

To date, there are few—perhaps just a couple—peer-reviewed papers seriously entertaining the lab leak idea. Meanwhile, there have been numerous credible studies pointing to COVID-19’s natural origins. An exhaustive study published in Nature Medicine in March 2020 found “SARS-CoV-2 is not a laboratory construct or a purposefully manipulated virus.” One of the paper’s authors, Kristian G. Andersen, said in a statement that the conclusions in the paper “have only since been further strengthened by additional evidence, of which there is a great deal.”

One of the most effective parts of the lab leak theory is not the quality of evidence but the quantity. Bits and pieces are fired out at a rapid pace, some of them even contradicting each other, before they can be adequately discussed or broken down.

“What does it mean that three people, out of a large research staff, were sick with flu-like symptoms in flu season?”

Take the report of the sick lab workers: “What does it mean that three people, out of a large research staff, were sick with flu-like symptoms in flu season?” Goldstein said. Snappy headlines highlighting that the workers “sought hospital care” fall apart when the context is considered; in China, primary care is largely delivered through hospitals, and sick notes are compulsory for time off. Visiting a hospital in Wuhan was the equivalent of a trip to the doctor’s office in the United States.

Cheryl Rofer spent 35 years as a chemist at the Los Alamos National Laboratory and specializes in arms control. She spent years handling plutonium in tightly controlled and highly secretive lab environments. “If these people became ill while working on a weapons program, or gain-of-function research, or anything like that—they would not go to a hospital,” she said.

Even the damning coincidence of the lab’s proximity to the outbreak is weak. It’s not certain that Wuhan was the origin of the virus, rather than simply where it happened to first be detected. As with SARS, the virus may have originated hundreds of miles away and gone unnoticed amid China’s underdeveloped rural medical system even when it jumped to humans. How SARS spread in 2003 makes a mockery of Wade’s claim that the distance involved is implausible.

Recently, the Daily Mail and New York Post trumpeted an “explosive” new study that supposedly offered firm proof that the COVID-19 virus was man-made. One of the paper’s authors told the Mail that four positively charged amino acids in the virus’s genetic makeup were the key evidence: “The laws of physics mean that you cannot have four positively charged amino acids in a row. The only way you can get this is if you artificially manufacture it,” the author told the British paper.

“It has gotten utterly crazy. Even intelligent people are just losing it.”

Scientists wasted no time shredding the idea. One, calling it “unbelievable bullshit,” pointed out that a third of the proteins in the human body carry that characteristic. As another noted , “even man-made things must obey the laws of physics.”

“It has gotten utterly crazy,” Rofer said. “Even intelligent people are just losing it.”

Claims about the intelligence community’s conclusions must be viewed with a careful and cynical eye as well. U.S. intelligence contains a huge range of agencies—some with much better hit rates than others, and none of them geared toward answering complicated scientific questions. An exhaustive Vanity Fair feature, digging into the intelligence community’s inquiries—or lack thereof—provides much fanfare to the same meager pieces of evidence offered by Baker and Wade. The story provides the backstory to Pompeo’s brash claims of “enormous” evidence for the lab leak. The story reveals that a team inside the State Department’s Bureau of Arms Control, Verification, and Compliance had doggedly pursued the theory as recently as this January. The feature alleges that Christopher Ford, then the undersecretary of state for arms control and international security, was “so hostile to their probe that they viewed him as a blinkered functionary bent on whitewashing China’s malfeasance.”

In a lengthy rebuttal, Ford notes that he actually supported the lab leak theory—his main crime, it seems, was insisting that the conclusion that COVID-19 was a lab leak be put to independent experts. When those independent experts got a look at the State Department’s analysis, he wrote in an email at the time, they found it rested on a single statistical analysis prepared by one scientist “a pathologist, rather than a virologist, epidemiologist, or infectious disease modeler” without expertise in that type of modeling. The “statistical case seems notably weak,” Ford wrote.

CNN reported similar problems: “The way they did their work was suspicious as hell,” one source told the network, adding that “it smelled like they were just fishing to justify predetermined conclusions and cut out experts who could critique their ‘science.’”

Rofer knows all too well that bad lab security can lead to accidents. She tells the story of 6,000 sheep who died as a result of a secretive U.S. military chemical weapons test in Utah in 1968. Even “Los Alamos has had a couple of plutonium incidents,” Rofer said. And, of course, the world has seen cases of anthrax and SARS due to lab leaks.

The difference is that these are all already-known viruses and compounds. The H1N1 outbreak in 1977 appears to have come as a result of a live vaccine trial—in an attempt to inoculate soldiers, the Soviets appear to have accidentally infected them.

At its most benign, the lab leak theory holds that China discovered a completely new and dangerous coronavirus, didn’t tell anybody, and didn’t sequence it or develop a vaccine, then let it get out without noticing or while failing to contain it.

Keeping this work secret is easier said than done. Researchers at the Wuhan lab frequently cooperated with American and Canadian counterparts on coronavirus research—we know about the security flaws specifically because American officials toured the facilities. The Wuhan Institute of Virology publishes findings from its coronavirus research frequently, as part of China’s goal to become a scientific superpower. We know as much as we do about coronaviruses because of the Wuhan lab’s research into the caves in Yunnan.

The real clues about COVID-19’s origin aren’t geopolitical but scientific.

The real clues about COVID-19’s origin aren’t geopolitical but scientific.

The lab leak theory says the furin cleavage site, a tiny enzyme dangling from the virus, is key to understanding the novel coronavirus’s origin.

Goldstein agrees. But, he said, that cleavage site actually points toward the virus’s natural origin.

“You cannot, in a normal cell culture, maintain the furin cleavage site,” he told me. When the COVID-19 virus is replicated in a cell culture in a lab, he said, the furin cleavage tends to delete itself. A peer-reviewed paper, published in late April in Nature, noted that habit and identified seven other papers that found a similar deletion.

So if researchers were using traditional methods and their preferred cell lines to try to force the virus to replicate, mutate, and change, the furin cleavage site would likely disappear.

The gain-of-function proponents say this furin site is too well adapted for humans to be an accident. But Goldstein said the opposite is true. The cleavage site is imperfect, so odd, that it could have only been a freak of nature. “No virologist would use that cleavage site,” he said.

It is possible to replicate the virus in a lab while preserving the cleavage site, Goldstein added, but it would “require doing things differently than everyone does them.” And, crucially, it would require them choosing cell cultures that replicate the virus more slowly.

So the researchers would have had to make a series of inefficient and strange decisions to preserve a tiny, novel, odd enzyme. Indeed, the researchers at Imperial College London behind the April Nature article found that the addition of four amino acids in the virus’s spike protein “occurred during its emergence from an animal reservoir and created a suboptimal furin [cleavage site].” Another study published in January in Stem Cell Research demonstrated how these furin sites naturally evolve in many coronaviruses.

And what about RaTG13, the virus that Wade and Baker argue is so similar to COVID-19 that it would only need some tuneups? In a statement from April 2020, Edward Holmes—an evolutionary biologist and virologist at the University of Sydney—noted that “the level of genome sequence divergence between SARS-CoV-2 and RaTG13 is equivalent to an average of 50 years (and at least 20 years) of evolutionary change.”

“Hence, SARS-CoV-2 was not derived from RaTG13,” Holmes said. Backing up what numerous other researchers have found, Holmes added that “the abundance, diversity and evolution of coronaviruses in wildlife strongly suggests that this virus is of natural origin.”

“Cramming 50 years of evolution into eight is impossible,” Goldstein said. “Forcing 1,000 nucleotide changes—just, no.”

But maybe this gain-of-function research did not try to replicate the virus in a petri dish but, instead, used live animals to multiply and mutate the virus—using one sick animal to infect the next, and the next, and the next, until an evolved and efficient virus came out the other end.

Following the theory down this path gets increasingly fantastical. “How complicated can this get?” Goldstein said. It would be significantly more expensive, labor-intensive, and difficult to hide. The lab would need to run a veritable petting zoo of different animals to perfect this kind of zoonotic transmission. And it still doesn’t account for the decades of necessary evolution.

Prior to the outbreak in December 2019, nothing closely resembling the COVID-19 virus was reported in any lab. Since it has emerged, it has taken hundreds of millions of infections to net just a handful of serious mutations and variants.

“We’re not good enough, in virology, to make the perfect virus,” Goldstein said.

Nature, however, is.

Our best available theory is that COVID-19 likely originated in bats, quite likely from the same caves that begot SARS, and jumped through two other animals before reaching humans. Those three hosts led to a “complex pattern of evolutionary recombination.” Researchers have found close relatives to COVID-19 in pangolins and raccoon dogs, making them prime suspects in the so-called spillover event. While the Wuhan seafood market’s role in the pandemic is still unclear—whether it was truly the origin or just the first major outbreak—new research suggests it may be key to proving the natural origin theory. Despite insistence from Beijing that no live animals were kept at the market, a new paper in Scientific Reports reveals photographic evidence that raccoon dogs were kept at the wet market. “Almost all animals were sold alive, caged, stacked and in poor condition,” the researchers found.

This theory would mean COVID-19 jumped between three different animals and traveled about 1,000 miles.

Compare that with SARS: The virus went through two animals and traveled about 900 miles before leading to outbreaks in humans.

For the lab leak theory to work, the Wuhan lab would need to have either found a completely novel and hyperinfectious virus in the wild and kept it in a lab without telling anyone, or engineered that virus in a way that would stun scientists at more advanced American labs by truncating decades of evolution into just a few years.

Then, there would need to have been a catastrophic breach of safety protocol that infected one or more staffers from the lab—but also, the accident would need to have gone unnoticed, so that they simply walked out of the building when their shift was done.

“It sounds simpler than the alternative, but when you get into it, it’s much more complicated,” Goldstein said.

Peter Ben Embarek is a World Health Organization food security expert, tapped by the internationalist organization to fly to Wuhan and investigate the origins of the virus.

“The idea is to get the studies that are needed to get a better idea of the origin of the virus,” Ben Embarek told me in January. He and his team were headed to China agnostic about what, exactly, had caused the pandemic. “The approach is precisely not to follow all kinds of hypotheses,” he said. The science confirms the COVID-19 virus is a “natural virus,” not a bioweapon. But he acknowledged that “accidents happen” and they could not, then, discount the idea it had escaped from a lab.

I asked him about the lab leak theory. “This ‘growing body of evidence’—we haven’t seen it,” Ben Embarek said.

In a Feb. 9 press conference, after several weeks on the ground, Ben Embarek and his colleagues announced that they had seen enough to conclude that the lab leak theory was “extremely unlikely.”

“There had been no publication, no reports of this virus, of another virus extremely linked or closely linked to this, being worked with in any other laboratory in the world,” Ben Embarek noted then.

The scientific conclusions of the WHO study seem compelling. But of course the organization’s conclusion only served as proof, for many, that the opposite is true, given the organization’s considerable support from Beijing. WHO staff themselves have said the Chinese government stymied the investigation. Beijing tried to manage what researchers and journalists did, and didn’t, see. It punished Australia after Canberra called for an independent investigation into the coronavirus’s origins.

But China’s secrecy and tendency toward cover-up aren’t proof of any particular conspiracy. That paranoia is Beijing’s default.

Chinese officials always scramble to avoid blame after disasters, natural or otherwise. After the Sichuan earthquake of 2008, for instance, protesting parents whose children died in the quake were arrested, and reporters who attempted to look into construction scandals were detained and censored. It happened, as well, around the Tianjin explosion of 2015 and the Wenzhou train crash of 2011. And it happens around smaller, unnoticed tragedies on a daily basis. Individual officials are eager to avoid being scapegoated—and the central government seeks to present a simple, propagandized image of competence and compassion.

China tried to cover up SARS, downplaying case counts and even forbidding WHO researchers from visiting the site of the initial outbreak. As one Chinese politics expert told the Times in 2003, SARS “became a serious political problem for the government as well as a medical one.”

History repeated itself in 2020 as authorities suppressed those trying to raise the alarm about a possible “second SARS” outbreak, such as late doctor Li Wenliang.

When it comes to the Chinese Communist Party, cover-up is business as usual.

Over the past year, I’ve spoken with a slew of researchers, scientists, and public health experts: Their takes on the origins of COVID-19 generally fall into two camps. Most say that the virus is very likely natural and that theories around the Wuhan Institute of Virology are a possible explanation, but they’re unlikely. The other group, a minority, says both theories are more or less equally valid and that the lab leak theory is in desperate need of more study.

It’s hard to fault either camp.

But not all research is created equal.

Both Baker and Wade, for example, cite the husband-and-wife duo behind the Bioscience Resource Project, which published a paper last summer promoting the Mojiang miner theory. The project, however, largely focuses on crop science and has pushed junk science and misinformation about genetically modified organisms . Since the start of the pandemic, the group has pivoted toward taking on what they call “the pandemic virus industrial complex.”

One oft-cited editorial was written by a number of researchers who do not specialize in virology. The team of experts cited in the Vanity Fair article are mostly anonymous. Another prominent webpage compiling evidence for this argument, which Baker and Wade relied on heavily, is entirely anonymously produced.

And, of course, it’s hard to divorce many Republicans’ clear preference for the lab leak theory from their default position that China is a threat to global security.

Were some people, myself included, too glibly dismissive of the lab leak theory early on? Can a theory be right even when it’s pushed by bad actors for political ends and crank theorists? Sure. But that doesn’t mean the possibility wasn’t being actively explored. It was. There was not a conspiracy to silence research or speculation about the Wuhan lab.

Yet even after more than a year of study, the odds that the lab leak theory is correct remain roughly the same as when it was reported on a year ago—it’s theoretically possible but far less likely than zoonotic origin.

The origin of this virus matters. Yes, if Beijing is culpable for the origin of the novel coronavirus it merits repercussions—and even if it is not, China still needs to be held accountable for its obfuscation.

If the caves of Yunnan and the surrounding ecosystem gave us two highly infectious coronaviruses in two decades, there is no telling when the next such coronavirus could emerge—or from where.

If the COVID-19 virus, as previous viruses have done, hopped between various animals, perfecting its ability to infect humans along the way, it’s another indicator of how humanity’s intrusions into wilderness are unearthing new pathogens at a worryingly fast rate. That requires a substantial rethink of how we settle the Earth and how we manage wild nature.

That, of course, is a more unsettling prospect than simply blaming Beijing.

Discovering, with absolute certainty, the exact origin of COVID-19 may be impossible. But it is crucial that we let science, not hype or anxiety, determine the possible scenarios.

As Rofer told me: “We all feel a loss of control. And a way to understand this is to understand the origin.”

Correction, June 16, 2021: The March 2020 article cited was published in the journal Nature Medicine. A previous version of this article misstated the name of the journal. This article was also updated to clarify that Kristian G. Andersen was a co-author, not the sole author, of the study cited.