I would assume he's referring to the fact that evolution works by allowing the weak to die, or at the least not reproduce and without those mechanisms evolution is a different beast.
E.g. I believe HIV resistance is higher amongst people that have a certain gene that appears to have spread to something like 10% of people in Northern Europe after the black plague, for example. And blond hair in Northern Europe spread out of the Baltics from as recently as the 1700's, and went from nothing to 90%+ of the population in some areas.