Why is it E?

@sb lines 31 to 33 give the specific question that has thrown Sanders' hypothesis into question, which (E) essentially restates. While they provide information as to why Sanders' hypothesis is incomplete, the other answers don't do anything to challenge his hypothesis. The body of information that Sanders missed was the strange dispersal of species within the Amazon. Does that make sense?

Yes, that makes sense. Thank you!

No that does NOT make sense. How could he (Haffer) "propose a compelling explanation for the distribution of species." And from there, line 35, onward, the author goes into explaining Haffer's compelling proposed hypothesis, and still fail to account for the proposal?

Answer choice E comes NOT from the lines 31 to 33 that Mr. Christopher above quoted; but rather from lines 54 and 56 which states "no conclusive proof has yet been to support Haffer's hypothesis." No proof, then no account. Lines 31 to 33 have nothing to do with this question, or answer choice E.