Sure its evolutionarily possible to insert 12nt. Inserts are not common though. Whats key is that the insert -in a 30kbp sequence was at exactly a position that would give it functional properties to allow the virus much higher tropism for human tissues. Furin cleavage site appear to selected against in bats.
There is no known source from where it came from, coronaviruses often recombine, but there is no other known sarbecovirus from where the fcs could have come from.
Bob Garry tries to explain away his documented "I cant think of a plausible natural scenario for how this 12nt insert occurred" in an interview here.
What is often totally ignored by virologists and evolutionary biologists with potential funding to loose if a kab origin is proven is that the WIV was partner in a proposal to insert exactly the sort of furin cleavage site we see in SARS-CoV-2
Then like magic (a unicorn as Bob Garry says) a SARS-related CoV appears, appears down the road from the lab, that is highly infectious to humans, with the first ever furin cleavage site in a sarbecovirus, which even Zhengli Shi says was a recent inroduction to humans: "almost identical sequences of this virus in different patients imply a probably recent introduction in humans"
Lab escape through a lab acquired infection with a SARS related virus is by far the most likely scenario and should be the default hypothesis to disprove.
Natural origin scenario requires a series of events to occur, each very unlikely.
There is no known source from where it came from, coronaviruses often recombine, but there is no other known sarbecovirus from where the fcs could have come from.
Bob Garry tries to explain away his documented "I cant think of a plausible natural scenario for how this 12nt insert occurred" in an interview here.
https://youtu.be/4-FhwghrSLs
What is often totally ignored by virologists and evolutionary biologists with potential funding to loose if a kab origin is proven is that the WIV was partner in a proposal to insert exactly the sort of furin cleavage site we see in SARS-CoV-2
https://theintercept.com/2021/09/23/coronavirus-research-gra...
Then like magic (a unicorn as Bob Garry says) a SARS-related CoV appears, appears down the road from the lab, that is highly infectious to humans, with the first ever furin cleavage site in a sarbecovirus, which even Zhengli Shi says was a recent inroduction to humans: "almost identical sequences of this virus in different patients imply a probably recent introduction in humans"
https://www.biorxiv.org/content/10.1101/2020.01.22.914952v1
Lab escape through a lab acquired infection with a SARS related virus is by far the most likely scenario and should be the default hypothesis to disprove.
Natural origin scenario requires a series of events to occur, each very unlikely.