The theory (as this part of it was taught back in my day) was that the new species being more effective than the one it just ‘descended from’ therefore would out-compete for the same resources and push the old species into extinction.
Then you were taught it poorly.
551 posted on 09/16/2008 6:23:14 AM PDT by Sloth
(Pontius Pilate voted 'present'; Barrabas was community organizer.)