proximal origin
The proximal origin of
“It is improbable that SARS-CoV-2 emerged through laboratory manipulation of a related SARS-CoV-like coronavirus.
As noted above, the RBD of SARS-CoV-2 is optimized for binding to human ACE2 with an efficient solution different from those previously predicted.
Furthermore, if genetic manipulation had been performed, one of the several reverse-genetic systems available for betacoronaviruses would probably have been used. However, the genetic data irrefutably show that SARS-CoV-2 is not derived from any previously used virus backbone.
Instead, we propose two scenarios that can plausibly explain the origin of SARS-CoV-2:
(i) natural selection in an animal host before zoonotic transfer; and
(ii) natural selection in humans following zoonotic transfer.”