1. Direct-jump from bat population
2. Started in bats, came to humans through intermediate animal
3. Came from frozen food outside of China
4. Lab accident.
I used to think the lab accident theory was crazy, because it sounds like a science fiction movie. Not an impossible theory, just a crazy one.
But according to this article, despite a year of investigation, (1) is unlikely because we haven't found anyone that interacted with the nearest bat population hundred of miles away that didn't work in the virus lab in Wuhan and that caught the virus, (2) is unlikely because we would have found the intermediate animal by now, (3) is unlikely because the first case found was in China (and not somewhere else... if frozen food had the virus, the food would have had it before it was frozen, and someone else would have had it), and (4) is unlikely because a government famous for blocking information and is paranoid about how it is perceived domestically and internationally says "No, trust us on this one."
At some point, crazy theories become the most likely. Hopefully I'm wrong though, and they find an explanation that isn't "lab accident." It seems like we should be studying viruses and sharing that information with each other, and accidents like this will make it more likely that such research doesn't happen.
2) is also likely, for some viruses it took years and years, sometimes even more than a decade to find the actual intermediate animal.
4) is unlikely because further analysis cannot produce a likely scenario. If the virus was from an animal source known to the lab, we would know already, and if it was due to a gain-of-function experiment, it would be quite unlikely for the virus to take so much time to adapt to humans (it still hasn't fully done so), and there is still a lot of function to be gained. Besides, there is no obvious marker for genetic engineering (the furin cleavage sites are perfectly well described by both 1 and 2), and the fact the virus does not seem to be at a local optima yet indicates that it's probably not the result of engineering by repeated selection.
Unless they started commanding to destroy samples, and sharing sequences of captured bats after the pandemic started.
> it would be quite unlikely for the virus to take so much time to adapt to humans
All experts agree that SARS-COV-2 is extremely adapted to human infection. Like it appeared out of nowhere, not the gradual result of a natural spill-over. To pose: "It could have been even more infectious" as an argument against gain-of-function is not very strong. And if we agree that China did not deliberately release a finished product, it would be weird to see optimal adaptivity.
> there is no obvious marker for genetic engineering
Gain-of-function does not create obvious marker. It is known possible to increase GoF of coronavirus using techniques that produce no markers at all. It is also tying it too closely to engineered bioweapons (vanilla SARS-COV is a bioweapon itself, even if collected from civet cats by terrorists), because the lab leak could also have been from a collected sample and accidental escape. There is no genetic engineering there at all.
Which is exactly what they started doing back in February (2020). The two labs in Wuhan were ordered to destroy all samples they had. So even if the theory were to turn out to be the most likely origin, we'd have no way to find out for sure.