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Complete Question Explanation
(See the complete passage discussion here: lsat/viewtopic.php?t=14508)

The correct answer choice is (E)

This is the most diffi cult question of the passage. In reviewing the question stem, you must read
carefully in order to note that you are weakening the author’s criticism of the supposed evolutionary
trend towards symbiosis. As you may recall, the author noted in lines 53-55, “Fungi both harmful
and benign can now be found both early and late in fungus evolutionary history, and that
consequently fungi can evolve towards symbiosis but then move just as easily back to parasitism.
You need to select some evidence that helps demonstrate that the overall trend, despite the author’s
evidence, is toward symbiosis (and, once there, does not move easily back to parasitism).

Answer choice (A): Since this information is entirely consistent with the assumption that fungi
evolve toward greater symbiosis, this response would not weaken the author’s critique.

Answer choice (B): The comparison of the fungi “family tree” to that of other organisms is entirely
irrelevant to the issue, and the relative complexity of the fungi evolutionary tree does not indicate
anything about the development of that tree.

Answer choice (C): Whether or not the DNA of symbiotic versus parasitic fungi is more diffi cult to
isolate is irrelevant to the correctness (or lack thereof) of the author’s conclusion that fungi do not
evolve towards symbiosis. You should not conclude that any relative diffi culties led to imprecision
and inaccuracy in research.

Answer choice (D): You should eliminate this response immediately, because its meaning is actually
consistent with the author’s criticism of the assumption in lines 50-55. If parasitic fungi sometimes
evolved much later than symbiotic fungi, that might help criticize an assumption that evolution
proceeds toward symbiosis.

Answer choice (E): This is the correct answer choice. The evolutionary assumption that parasitic
fungi evolve to become symbiotic so as not to destroy the host must be based on the idea that
fungi are more likely to survive in a symbiotic relationship. If it is true that fungus that return from
symbiosis to parasitism usually die out, that confi rms the basis of the evolutionary assumption, and
that would weaken the author’s critique. Furthermore, the answer states that fungi that turn back
toward parasitism usually become extinct fairly soon thereafter, suggesting that there really isn’t any
signifi cant evolution toward parasitism. The “regressive” branches can be seen as failed branches,
and you are expected to know that evolution doesn’t consist purely of promoting certain organisms—
it also consists of the extinction of others. If, as this answer choice states, “regressed” fungi quickly
die out, the temporary existence of regressed, parasitic fungi is irrelevant and the assumption that
evolution drives toward symbiosis may be valid.
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Hi guys,

The author, with the recent research, can support his criticism that the long-standing evolutionary assumption that parasitic interactions inevitably evolve from parasitic to symbiosis. Choice E says that fungi that evolve from symbiotic to parasitic dies inmediately. How can Choice E weaken the author's criticism? I don't see it clearly.

My rationale is the following:

1) Author's Criticism
Parasitic :arrow: Symbiotic forever

2) Author in the last sentence of the last paragraph
Parasitic :arrow: Symbiotic :arrow: Parasitic forever

3) Choice E
Symbiotic :arrow: Parasitic :arrow: Dies rapidly

So, 2) is part of the author argumentation as supporting his criticism on 1). Choice E attacks 2), therefore also attacks whole author argument/position. I just end at this point but semantically I still don't see why E is the correct answer. For instance, a correct answer for me is one like this "Recent research has demonstrated that parasitic fungi has evolved to symbiotic and has lasted there for several years". That attacks directly the author's criticism.

Thanks for your help.
 Kristina Moen
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Hi gintriag,

Keep in mind that you are looking to weaken the author's criticism of the assumption that parasitic interactions generally evolve toward symbiosis. He concludes from the evidence he presents 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." (last line).

So anything that strengthens the assumption that parasitic interactions generally evolve toward symbiosis will be the correct answer.

Answer choice (E) strengthens this by showing that fungus that evolve to parasitism usually dies out. Thus, it weakens the author's claim that fungi can evolve toward mutualism and "just as easily turn back again toward parasitism."

Hope this helps!
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thank you, may I ask if it is right to simplify the reasoning in this way:
Author: P-->S+S-->P;
Evolutionary: P-->S;
Our job is to weaken the author, so we need to show S-\\->P, Therefore E.



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