This question is one where a part of the reason that answer choice E is so tempting is that the passage uses unfamilar words to describe Sibley. We're told he was "one of the fomenters [of the phylogenetic species concept]". I originally didn't know what a fomenter was, but from the context of the passage I thought it might be something like a frontrunner or a pioneer. Couple that with the description of his revolutionary DNA techniques, and choice E seems reasonable.

If you knew the definition of the word, i.e. someone who instigates or rouses (usually rebellion or discord of some kind in historic context), you might not be caught up in this. "Provacateur" sounds a lot less like "pioneer"...