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It's often stated almost as a truism, and apparently accepted by Redfield, that a virus crossing from animals into people has to undergo rapid adaptation to become transmissible in humans. While that may often be true, it doesn't have to be. We know SARS-CoV-2 itself can jump seamlessly between hosts – it's gone multiple times from humans into minks and spread like wildfire. It transmits perfectly well among hamsters and ferrets in the lab. If a human virus can transmit among mink, there's no basis to assume a bat virus can't transmit among humans. Us humans may think we're very special – but to a virus we are just another mammalian host.

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Redfield's more sinister claim – that Chinese researchers passaged this virus repeatedly to make it grow better and thus adapted it to human transmission in the lab – simply doesn't hold up. A study from late 2020 in PLoS Biology demonstrated that the ability of SARS-related coronavirus spike proteins to bind to human cells is naturally evolving in the viral milieu, and a more recent not-yet-peer reviewed study found that SARS-CoV-2 isn't even unusually good at doing so; the spike of a closely related virus found in pangolins initiates infection of human cells much more effectively. SARS-CoV-2 is still adapting though. The spike protein from the B.1.1.7 variant acts a lot more like the pangolin virus spike protein. Evolution never stops.

More fundamentally, adaptation to human transmission and virulence is exactly the opposite of what we'd expect from serial passage in cells or animals. This exact process is a classic way of weakening a virus to make a vaccine – the oral polio vaccine developed by Sabin and the yellow fever vaccine have used this approach, among many others. That's because viruses evolve virulence and transmission in a complex host system. If you extract them from that system and force them to evolve in a different context (like in cells outside a body) they "de-adapt" to the "real world," precisely the opposite of what Redfield suggests. Frankly, it's hard to understand why he wouldn't know that.