Isn’t This is just basic biology though? You can read up on viruses for 20 minutes, and reach this conclusion. Viruses mutate becoming less lethal, and increase their survival and chance to spread.
Sort of. Pathogens evolve to become more easily spread, which
usually means becoming less lethal. There have been a few cases throughout history where a disease remained extremely dangerous throughout basically its entire existence while still being extremely good at spreading, like smallpox. Those are usually extremely old diseases that aren't Coronaviruses, though, so they're not a good model for a recent spillover in that grouping. Smallpox doesn't even have the same kind of genetic material as SARS-CoV-2 (it's a DNA virus; CoVs are RNA viruses) and entered the human population thousands of years ago, long before any kind of systematic public health measures or medical strategies to manage spread. It existed for ages, but we wiped it out over the course of just a few centuries.
The only probable model we have for a Coronavirus spillover is one of the H-CoVs, which based on the majority of the evidence followed a course similar to what Covid-19 seems to be doing. Based on the best available molecular clock and environmental evidence the last time I read anything about it, it was a Beta-Coronavirus that first spread from ruminants (probably cattle) somewhere in Central Eurasia during a time frame of a few years centered around the timing of the Russian "Flu" pandemic in the late-19th century. It then evolved to be much better at spreading while having symptoms mild enough to be a less frequent cause of the common cold, which is a symptom- rather than pathogen-based diagnosis usually caused by either rhinoviruses or the other H-CoVs.
So, he was probably either aware that this is a common behavior for diseases, or possibly even of the Russian Flu example since it was discovered within a year of Covid-19 being declared a pandemic. While not technically a guarantee, this wasn't exactly an original thought on his part or a tough choice on where to bet.
You banged a pirate dude, and now you're on the Faaaaaarms 
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