Thread by @Ayjchan

I became infamous for writing that SARS-CoV-2 might have adapted for human infection and transmission in a lab, alongside other plausible natural scenarios.

But top experts had also been saying the same thing, just without pointing out that the virus might've come from a lab.

I was actually annoyed when @antonioregalado pointed this out to me earlier this year. That even the Proximal Origin authors had discussed how was it that SARS-CoV-2 had (pre-)adapted for humans.

@antonioregalado Some ask, why are we seeing new variants if SARS2 was well adapted for humans in Dec 2019?

Because viruses don't stop evolving. If we had run the well adapted SARS1 through 300 million people across every race and health condition, we would've also been overrun with variants.

@antonioregalado Think of evolution in terms of a virus exploring a fitness landscape full of peaks and valleys.

In an emerging outbreak, the virus is exploring a local peak. If, after reaching that local peak of fitness, you let the virus continue to explore endlessly, it will find new peaks.

For SARS1 we saw numerous adaptive mutations in its first months of transmission that made the virus better at infecting humans, several in the spike receptor binding domain alone.

But SARS2 only had 1 of these adaptive mutations: D614G.

science.org/doi/10.1126/sc…

Independent groups of scientists have since analyzed the evolution of SARS-CoV-2 in mink and assessed that there was rapid host adaptation of the virus to mink (new host species) but not in humans.
biorxiv.org/content/10.110…
biorxiv.org/content/10.110…