There has been an extensive analysis by a virologist on Reddit[¹], who claimed that, very simply, SARS-COV2 is a so-called "mosaic" virus, while man-made viruses are inevitably "chimera" ones. The article does not seem to make this distinction.
The virologist also chimed on HN (besides, calling BS on people who were, out of ignorance, spreading false beliefs), but it seems he's not participating to this post.
It'd be best to have the opinion of a specialized scientist, in order to to have scientific clarity before starting the political arguments.
[¹]=https://www.reddit.com/r/science/comments/gk6y95/covid19_did...
If I take a known virus and make a single mutation (insertion of a furin site in this case), then I wind up with the same virus, + a furin. If I take that mutated virus, and then passage it through multiple generations in lab grown hosts, it will mutate at random throughout the genome.
The exact rate and the time it would take is heavily debated, but one important note is that viruses with an RNA-dependant RNA polymerase are, as an evolutionary strategy, quite poor at preserving their own genetic information. They have the highest error rate of replication of any known organism. Which means, after some discrete amount of generations, you could wind up with some sort of "mosaic" + "chimeric" virus. Again though, how many generations is under hot dispute. And how long that would take in nature vs in a laboratory is also under hot dispute.
100% of the evidence for lab leak is circumstantial. But we know two things:
1) If I set out to design a SARS-CoV 2, it's technically feasible. And there's reason to be interested in this type of research. And lab accidents involving pathogens can and do happen.
2) There's no single piece of evidence concretely and completely ruling it out. Which is unfortunate.
I'm a structural biologist, I primarily study viruses, I also engaged heavily in that topic you mentioned (against my better judgement). At the moment, I have a mental probability (which is probably incorrect) of wild virus 90% chance, lab leak 10% chance. I'd be extremely surprised if it was a lab leak, but I also can't sufficiently falsify that hypothesis to complete write it off.
I just have a hard time understanding why so clear evidence of the epidemic starting outside Wuhan is missing from the debate, so I'd appreciate if you could comment on it.