Questions of origins and questions of disease control are not the same thing once human-to-human transmission has become common, said Deborah Seligsohn, an expert in environment and public health at Villanova University. There are probabilities, and there are possibilities, said Banerjee. HOW IMPORTANT IS IT TO UNDERSTAND THE ORIGIN? Confirming with 100% certainty the origin of a virus is often not fast, easy, or always even possible. While the closest known viruses to Covid-19 have been found in bats, the 'evolutionary distance' between them is thought to be 'several decades'.
change in modern transmission distances is rare.
( z0 rare :ARG1 ( z1 change :ARG1 ( z2 distance :ARG1-of ( z3 modern ) :mod ( z4 transmit ) ) ) )
(z0 / rare-02
    :ARG1 (z1 / change-01
              :ARG1 (z2 / distance
                        :ARG1-of (z3 / modern-02)
                        :mod (z4 / transmit-01))))
change in modern transmission distances is rare .
z2 :mod z4
z2 :ARG1-of z3
z1 :ARG1 z2
z0 :ARG1 z1