You do know, don't you, that Darwin's Origin of Species wasn't published until 1859?
Umm... Darwin didn't propose the theory of evolution until well after all the FF were quite dead. The FF were many things, but none of them could see into the future.
The FF also probably believed that bloodletting was a medically sound procedure since, at the time, people didn't know better. Just because people were ignorant in the past doesn't mean folks should be ignorant now that we know better.