> Furin cleavage sites very similar if not largely identical to this one have also been found in nature
I don't believe this is correct.
There are no other examples of a CoV within the sub-genera Sarbecovirus of a species/strain that shows evidence of insertion of a polybasic furin cleavage site.
Hi, never said they had to be within the sub-genera.
Recombination can absolutely happen inter-genera and even inter-family.
There's some evidence that Ebola got its VP40 from bats, or vice versa. Meaning that an RNA virus somehow got its nuclear regulatory factor from a bat. We have no idea in science how that happened. But we know there is homology! I can't find the link at the moment, but when I do I'll add it here. It's not actually that important to my argument.
There are also examples of inter-family recombination in viruses that are much more down to earth.
And you might be asking yourself, after reading that link "Why is it always bats?? Isn't that /suspicious/?" It's actually in keeping with everything we know about bats and their role as a viral reservoir. Lots of viruses cross paths in bats. See this other detailed post I wrote a while back: https://www.reddit.com/r/science/comments/gehvui/why_do_viru...
I just wanted to add that I probably was exaggerating when I said "we have no idea how that happened." re: VP40, bats, and ebola.
Best guess is: a retrovirus and an ebola-like virus infected a bat cell at the same time, the retrovirus accidentally picked up some of the bat genome, which then somehow recombined with the negative sense RNA genome of the ebola-like virus. We have no proof this happened like this, but it's the best guess.
Just as an example of the crazy things that we think probably happen in the world of viruses in nature.
I don't believe this is correct.
There are no other examples of a CoV within the sub-genera Sarbecovirus of a species/strain that shows evidence of insertion of a polybasic furin cleavage site.