After a hepadnavirus inserts itself

Answer choices

1. A

   Weak / No Impact26% picked this

   Viruses can affect the evolution of an organism and can thereby influence the likelihood of their

   The strength of wording like "some / sometimes / can / not all" means that one example is enough to make it true. This sort of weak wording is almost always wrong on Strengthen, Weaken, and Paradox. This answer seems to be trying to strengthen a connection between getting the hep virus and diverging into two species (so if there were a common ancestor to the junco/finch that got the hep virus, the hep virus may have influenced that species diverging 25 million years ago). But the weak strength of the answer makes it unappealing. We have no idea if the hep virus is one of the viruses that can influence the likelihood, and even if it were one of them, it's not a great answer. We don't need to be convinced that the junco/finch's common ancestor diverged into two species. We already know that that happened 25 million years ago. The fact that they diverged certainly doesn't prove that the species from which they came had a virus.

   26%
2. B

   No Impact15% picked this

   The chromosomes of the zebra finch and the dark-eyed junco contain fragments of no virus

   Whether the chromosomes do or don't have other virus fragments doesn't change this conversation at all. We know they both have the hep virus fragment; we know that the hep virus fragment gets sent down the lineage to all of an animal's descendants; and the author can still make the same argument whether or not either animal has other fragments lying around.

   15%
3. C

   Correct48% picked this

   When a virus inserts itself into an animal's chromosome, the insertion occurs at

   Why this is right

   This is a brutal correct answer, but it's helping to rule out the alternative explanation that the junco and the finch each got their hep virus from a different ancestor. If the hep virus inserts itself randomly, then it would be a 1 in a million chance that two organisms would magically get the hep virus inserted into precisely the same location of the same chromosome. Since the junco/finch have the fragment at the same exact spot, it would be almost unthinkable that they got it separately. It makes it much more likely that they got it from a common ancestor who passes it along to all its descendants in that same exact spot. Consider how the flipside of this answer would weaken -- if we heard that "when a virus inserts into a chromosome, it always inserts into the gap between chromosome 19 and 20", then that would make it very possible that the junco and the finch both got their virus fragment from different sources.

   Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.

   48%
4. D

   Weak Impact3% picked this

   Many bird species other than the zebra finch and the dark-eyed junco contain fragments

   This might seem to somewhat strengthen, if we think that "if all these birds are getting the hep virus, then maybe they all got it from some common bird ancestor more than 25 million years ago". But the author's case is that the junco and finch must have had a common ancestor, because they have the fragment at precisely the same location of the same chromosome, not because they're both birds. This answer choice doesn't do anything for us unless we know that these other bird species also have the fragment in the same spot, as well as whether these other bird species also diverged from the junco/finch at least 25 million years ago.

   3%
5. E

   Irrelevant: species' survival9% picked this

   The presence of a hepadnavirus in an animal species does not affect the likelihood of

   Nothing in this argument would be changed by whether the hep virus helps a species, hurts it, or is neutral to its survival likelihood.

   9%