Which one of the following, if true, most weakens the author's criticism of the assumption that parasitic interaction...

Marquisha on April 18, 2017

Why is the answer to this question E?

I was able to eliminate A and B but had trouble deciding between C D and E.

1 Reply

Mehran on April 26, 2017

Hey @marquisha, thanks for your question.

The author's criticism of the assumption that parasitic interactions generally evolve toward symbiosis is in the third and final paragraph of this passage; see Lines 45-50. The author's main argument in this section of the passage is that "given the new layout of the fungus family tree resulting from the lichen study, it appears that fungi can evolve toward mutualism and then just as easily turn back again toward parasitism."

For this weaken question, you want to try to undermine the author's claim.

Answer choice (E) does this. If it is true that branches of the fungus family tree that have evolved from symbiosis to parasitism *usually die out shortly thereafter,* this would undermine the argument that fungi can evolve toward mutualism and then *just as easily turn back again* toward parasitism. No, they cannot--rather, they usually die.

Answer choice (C) is irrelevant because even if the DNA of fungi involved in symbiotic interactions was far more difficult to isolate than that of fungi involved in parasitic interactions, that does not necessarily weaken or undermine the author's claim that "fungi can evolve toward mutualism and then just as easily turn back again toward parasitism." Put differently, the author's argument here has nothing to do with how simple or difficult isolation of DNA is.

Answer choice (D) is likewise irrelevant because it addresses the rate of evolution--rather than the question whether such evolution can go in two directions (toward mutualism, and then back toward parasitism) rather than in just one direction (inevitably to symbiosis).

Hope this helps! Please let us know if you have any additional questions.