So how many COVID-19 virons have there been?
In discussing various dubious fringe theories concerning COVID-19, PZ Meyers notes that a "low" 3% probability of a genetic occurrance ... becomes a near certainty when you have a viral population numbering in the trillions.
But is even that estimate sufficiently high? What is the global population of SARS-COVID-2 viral particles (virons)? And more impportantly, how many generations of virons have existed? My estimtaes here are still likely low but give some idea of scale.
An NIH preprint suggests 1-100 billion particles exist per human host.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7685332/
The human body, comparatively, consists of roughly one trillion cells. If everyone on Earth could get a piece of you, they'd each net about 100 cells.
Worldometers currently lists 180 million confirmed cases (certainly a major undercount, though for order-of-magnitude estimates, close enough).
https://www.worldometers.info/coronavirus/
It's easier to discuss these quantities in magnitudes rather than amounts, especially as multiplication and division become addition and subtraction. In magnitudes, we're talking of 10 to the power of the magnitued, so 3 is 10^3^, or a thousand, 6 is 10^6^, or a million, 9 is 10^9^, or a billion, etc.
In magnitudes, we're talking 9--11 virons per person and 8 persons, so 17--19 total viron particles globally.
That's 10^17^ -- 10^19^ particles. And likely far more with not only under-counted cases, but multiple generations of virus replication. Each individual viron is a genetic game, test, and outcome.
A trillion is 10^12^, subtracting magnitudes, we have 10^5^ -- 10^7^ trillions of particles, 100,000 to 10 million trillions.
At these scales, single-digit percentages are well within the error range of our estimate. Again, there are tens of thousands to tens of millions of occurrences of a 3% probability.
"Unlikely" is "overwhelmingly probable."
To be fair, PZ Meyers was referring to the likelihood of occurence of genetic variants in a lab setting. Roughly ten humans equivalent viral load would meet that trillion mark. And the same conclusion holds: 3% of a trillion remains an overwhelmingly large number (tens of billions), making the "unlikely occurrence", even if it were one, a certainty. The only question becomes whether it is a beneficial adaptation (from the viruses point of view) to the envrironment.
Which is us.
