The lab #OriginOfCovid hypothesis does not require that no natural spillovers of SARS-like viruses occur or that 0 SARS-like viruses have furin cleavage sites in nature.
It asks why a rare SARS-like virus + FCS emerged where scientists proposed putting FCSs in SARS-like viruses.
It asks why a rare SARS-like virus + FCS emerged where scientists proposed putting FCSs in SARS-like viruses.
These scientists wrote in early 2018 that they were systematically looking for rare SARS-like viruses with FCSs, and they would optimize/insert these FCSs into "low risk" SARS-like viruses to see how this could impact the virus' ability to infect and grow in human cells. 
One interpretation is that, at that time in early 2018, they had already found such rare SARS-like viruses and determined that they bore cleavage sites or features approaching functional cleavage sites that could be optimized and inserted into SARS-like viruses in the lab.
The only way we are going to understand if this research pipeline led to the pandemic virus is if we get access to research records from the lab in Wuhan or possibly communications between that group and their collaborators overseas, including in the US.
Scientists have been hunting novel SARS-like viruses since the 2003 SARS outbreak and none of these published SARS-like viruses have such a FCS.
It's possible this lab collected so many 100s of SARS-like viruses they finally found one with an FCS or something similar to an FCS.
It's possible this lab collected so many 100s of SARS-like viruses they finally found one with an FCS or something similar to an FCS.
In that sense, it is very unlikely that searching around in bat caves is going to tell us whether the pandemic virus emerged in Wuhan due to the wildlife trade or research activities.
What we need to know is what happened in Wuhan in the months leading up to the outbreak.
What we need to know is what happened in Wuhan in the months leading up to the outbreak.
Maybe someone can collect 10,000s of pathogen samples from animals and people across 8 countries like the Wuhan Institute of Virology lab did and one day find a SARS-like virus with a FCS.
This is not going to tell you how the pandemic virus appeared in Wuhan.
This is not going to tell you how the pandemic virus appeared in Wuhan.
It's going to tell you that if you collect 10,000s of pathogen samples from animals and people across 8 countries, you may find a SARS-like virus with a FCS.
And it is understood that if you work with such viruses at low biosafety levels like BSL2, they can escape from the lab.
And it is understood that if you work with such viruses at low biosafety levels like BSL2, they can escape from the lab.
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