TWO POSSIBLE theories broadly explain the origin of the coronavirus pandemic that has killed more than 3 million people. The first is the long-observed pathway of zoonotic spillover, in which a pathogen leaps from animal to human. The second is that a laboratory in Wuhan, China, was carrying out risky experiments with bat coronaviruses and could have suffered an accident or leak. Neither theory has proof, but as 18 prominent scientists caution, “both remain viable.” The world needs to know.

In a letter published in the journal Science last week, the scientists insist that “greater clarity about the origins of this pandemic is necessary and feasible to achieve.” The signers included Ralph Baric of the University of North Carolina at Chapel Hill, who is an expert on coronaviruses and pioneered techniques for manipulating them that were eventually used by the Wuhan Institute of Virology. The letter was organized by David Relman of Stanford University and Jesse Bloom of the University of Washington and endorsed by Rep. Anna Eshoo (D-Calif.), who chairs the House Energy and Commerce health subcommittee. The letter notes the lopsided deficiencies in an earlier World Health Organization-China investigation, and calls for a “proper investigation” that would be “transparent, objective, data-driven, inclusive of broad expertise, subject to independent oversight, and responsibly managed to minimize the impact of conflicts of interest.”

It is not too late. Surely, more research could fruitfully probe zoonotic spillover. Already, more than 80,000 wildlife, livestock and poultry samples were collected from 31 areas in China, and none tested positive for the virus before or after the outbreak.

The laboratory leak theory also deserves more careful scrutiny. This is not to stigmatize Asians or to bash China, nor to embrace the Trump administration’s use of the laboratory leak theory to divert attention from its failures. The reason to investigate is the persistence of unanswered questions about research being carried out at the Wuhan institute under Shi Zhengli to modify viral genomes to give them new properties, such as the ability to infect a new host species or transmit from one host to another more easily. The research involved testing novel chimeric viruses with different spike proteins, like that on the pandemic coronavirus strain, using “humanized” mice, with cells modified to resemble human respiratory cells.

Did some byproduct of the research leak, or did workers become inadvertently infected? Was the research carried out in less protected BSL-2 laboratories instead of the more secure BSL-4? Did Dr. Shi successfully manipulate a virus in the lab to add genetic features boosting affinity for human cells, as science journalist Nicholas Wade has suggested in the Bulletin of the Atomic Scientists? These and other questions have been met with stout denials and roadblocks from China. In response to the Science letter, which called for opening records of research labs, Dr. Shi said, “It’s definitely not acceptable,” and, “Who can provide an evidence that does not exist?”

That brings us no closer to identifying the pandemic’s origins. If the laboratory leak theory is wrong, China could easily clarify the situation by being more open and transparent. Instead, it acts as if there is something to hide.

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