Hey, thank you for your interest.

The article the quote is from was written a year ago, and I was trying to formulate what lab leak scenarios seemed possible at the time.

Since then, more evidence has emerged that basically eliminates all potential lab leak scenarios, including serial passage or mixes thereof.

To quickly answer your question:

- that SC2 was evolved through serial passage either in vitro or in vivo is highly unlikely, even if the engineers had an unknown CoV to start from. Natural evolution in the wild leaves different traces than passage in a lab; for example, recombination with other Sarbecoviruses. We know SC2 has a mosaic genome sharing different genetic histories; and we find recombination fragments related to SC2 out in nature (this is btw how Pekar et al., created their recCA genome for phylogeny)

- Cell culture systems for serial passage assert their own selection pressures; for example, SC2 loses the FCS in cell culture because of fast replication kinetics; cell culture or other animals (like humanized mice) would also leave different mutational signatores.

- the experiment as proposed is nonsensical; nobody would engineer in features that will then be lost in a serial passage experiment afterward

- serial passage in vivo is an enormous experiment from a facility, time, cost and manpower perspective. WIV did not have that.

- and lastly, no matter what proposition one wants to advance how a virus like SC2 might have been created artificially, it would just address problem the lab leak theory has, all the others remain. For example, the epidemiology, phylogeny, epidemic simulations and environmental samples all point towards the Huanan market as the center of emergence via at least two introductions. 2 lab leaks of slightly different viruses a week apart would not both show up at a market 16km away.

So yeah, the problem of lab leak is that no scenario is consistent with all the evidence.