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I think you've misunderstood the difference between the proximal and reservoir hosts, because your comment is almost entirely wrong. As noted in the article linked above, scientists researching the original SARS found the exact (within the few mutations expected on any short transmission chain) virus that infected humans in palm civets and raccoon dogs, within about a year. These are the proximal hosts, i.e. the hosts believed to have infected humans. Once a proximal non-human animal host is found, we can be very confident that the virus is zoonotic. Much later, Dr. Shi discovered that the greatest diversity of similar viruses was in bats. The bat viruses are less closely related to human SARS than the palm civet or raccoon dog viruses; but there's a lot of them, and they look ancestral. We therefore believe that the virus mostly evolved in bats, then was transmitted to the palm civets and raccoon dogs, evolved a little bit more there, and finally was transmitted to humans. This was very important in understand the evolutionary history of the virus, but provided no new information on how humans were first infected. Knowing one of the classes of host doesn't imply knowing the other: 1. For the original SARS, we found the proximal host within about a year. Much later, Dr. Shi found the reservoir host. 2. For SARS-CoV-2, we knew the reservoir host immediately, because it's closely related to the original SARS. After two years of searching, we still haven't found the proximal host. If one exists, the proximal animal host of SARS-CoV-2 is probably in China. Since China has seen low human spread (probably more than their official statistics, but clearly far less than the rest of the world), I don't see why you'd expect a human variant to displace the original zoonotic variant. There's also no particular evolutionary pressure for that--a variant evolved in humans might happen to be more transmissible in the proximal host animal, but that's not what's getting selected for when the virus is transmitted between humans. |