But the apparent DARPA grant proposal complicates these arguments, at the very least. The engineering work that it describes would indeed involve such an artificial insertion. We don’t know whether that work was ever carried out—remember, DARPA rejected this proposal. Even if it had been, several experts told us, the genetic engineering would have happened at Ralph Baric’s lab in Chapel Hill, about 8,000 miles away from where the SARS-CoV-2 outbreak started. Yet now we know that the idea of inserting these sites was very much of interest to these research groups in the lead-up to the pandemic. “This is the first time they reveal that they are looking for these sites,” said Alina Chan, a scientist in Boston and a co-author of the forthcoming book Viral: The Search for the Origin of Covid-19.

Stephen Goldstein, a postdoctoral researcher in evolutionary virology at the University of Utah and one of the co-authors of the pandemic-origins critical review, considers it “unlikely” that any such work would have gone forward in Wuhan. It would be unusual—even unethical—for a lab in China to pursue experiments that were originally proposed by one of its collaborators in the United States, he told us. Another co-author of the critical review, the Johns Hopkins University microbiology postdoc Alex Crits-Christoph, noted that the proposal doesn’t specify the virus into which any novel cleavage sites would be inserted. Unless the Wuhan lab had already isolated a SARS-CoV-2-like virus that could carry this insertion—which Crits-Christoph doubts, given the wording of the proposal—researchers at WIV would not have had enough time between early 2018 and the fall of 2019 to construct (and then mistakenly release) the virus at the root of the pandemic.

Still, these scientists agree that the very fact that these experiments were even on the radar raises significant concerns. “I recognize this revelation opens up legitimate lines of questioning that are serious and need to be addressed by the people involved,” Goldstein told us via email. Crits-Christoph said it pushed the existing evidence “one step closer to the lab-engineering hypothesis”—but added that, given the improbable timeline, it moved things “one step further as well.”