Coronavirus: Thread

Peter Fairbrother peter at
Tue Oct 27 00:07:59 PDT 2020

On 27/10/2020 04:28, jim bell wrote:
> On Monday, October 26, 2020, 03:25:41 AM PDT, grarpamp 
> <grarpamp at> wrote:
> Full disclosure:  While I consider myself conversant with many sciences 
> and technologies, 'biology' is probably my area of least knowledge.
> I rapidly skimmed this article, but was doubtful when I saw this:
>> "RaTG13 looks like a “close cousin” of the Wuhan coronavirus – the two are 96% identical throughout the whole sequence of the viral genome. If RaTG13 is a nature-borne virus, one can comfortably conclude that the Wuhan coronavirus must very likely also come from nature and must share a recent common ancestor with RaTG13."
> [end of quote]
> My impression is  that if two viruses are ONLY "96% identical"  
> "throughout the whole sequence of the viral genome", they shouldn't be 
> described as a "close cousin".   Should it be called a "not-so-close 
> cousin"?   I don't know.

RaTG13 has 29,855 base pairs, COVID has 29,844. Combined with 96% 
identical, that is is very close.

People generally find about 0.08% of a virus's RNA mutates per year, so 
a 4% change is about 50 years of normal mutation. It can be considerably 
faster than that though, that is only a very rough rule of thumb.

So overall the viruses are pretty close, but COVID probably didn't come 
directly from RaTG13, as the RaTG13 sequence is about 8 years old.

They most probably came from some common ancestor which split into the 
two strains - RaTG13 and the unknown strain which became COVID - at a 
rough guess about 17 years ago.

I say 17 years instead of the perhaps more obvious 25 or the less 
obvious 30 because the COVID evolutionary strain has crossed species, 
which tends to increase the mutation rate, statistically speaking, by 
changing a bunch of RNA all at once.

That would be fairly normal for viral evolution.

Peter Fairbrother

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