On Friday, 22 scientists published a commentary supporting a natural origin theory for SARS-CoV-2 in the journal Science China Life Sciences, citing evidence from evolutionary understanding and lack of proof of artificial tampering of the virus' genome.

The article came after 24 scientists around the world published an open letter in The Lancet medical journal this month stating that the virus most likely originated naturally, and not in a lab.

The commentary said SARS-CoV-2 is extremely well adapted to human populations compared to SARS-CoV in 2003, and it must have experienced a shift in adaptability from animal hosts to humans prior to the onset of the current pandemic through natural selection.

"In this view, SARS-CoV-2 could not have possibly evolved in an animal market in a big city and even less likely in a laboratory," the article said.

Wu Chung-I, the corresponding author of the article and a biology professor at Sun Yat-sen University in Guangzhou, Guangdong province, told China Daily that the virus' superior adaptability in humans was most likely acquired over a long evolutionary time frame as the virus accumulates a series of slight enhancements through random mutations.

Wu said the claim of a nonnatural origin for SARS-CoV-2 is moot since recent evidence based on mutational signatures shows that the virus' evolution has strictly followed natural laws to the letter.

The article said proponents of a man-made origin theory should be able to find genetic signatures that defy natural laws, such as bar coding commonly used in tracing cell lineages. Otherwise, "it would be more productive to focus on the natural processes in relation to the SARS-CoV-2 origin," it said.

Moreover, the article also points out that the virus will need to be screened by natural selection to be as adaptive as it is now.

Wu believes that prior to the COVID-19 outbreak, the virus may have undergone some forms of multistep evolution in human populations, resulting in its extraordinary adaptiveness. But how exactly this progress occurred remains a mystery.

"There may be a 'biological arms race' between the virus and its animal hosts at the place of origin, then the virus spread to a human population that does not have herd immunity to the new virus," he said.