In the widely accepted evolutionary theories, it is suggested that DNA evidences shows the evolution of different species in past. This can be proved as the similar or closely related organisms shows more genetic similarities as compared to the distantly related organism. In order to prove that DNA evidence shows that evolution from one species to another does not exists then the opposite must be true.
So, in this case, the scientist need to prove that DNA of the closely related individuals have less similarities as compared to the distantly related organisms.