I think it’s clear that Rush doesn’t understand the scientific method. It’s a common flaw. At least he hasn’t made creationism a central theme in his radio show. It actually took finding the missing link between apes and humans to get him to reveal his personal beliefs. He’s wrong, but as long as it doesn’t turn into a crusade, I’m willing to give him a pass.
As far as “cross-species” evolution, how about wolves to chiwawas? Somewhere there is a chiwawa screaming “My great granddad was not a wolf!”