#15 - Loggerhead turtles live and breed in distinct groups

[Administrator]

Complete Question Explanation

Weaken. The correct answer choice is (D)

The argument uses the premise that 95 percent of the DNA samples of Baja turtles match those
of Japanese turtles to conclude that Baja turtles hatch in Japanese waters 10,000 kilometers away.
Although this sounds like convincing statistical evidence (especially because most people are
conditioned to accept DNA-related evidence as irrefutable), the presence of statistics alone does not
prove the argument. For very rough example, consider the following statistic using DNA evidence:
humans and chimpanzees share about 98% of their DNA (we share about 75% of our DNA with
dogs, for that matter). The point is that mere percentages do not prove a definite connection (more
on this topic in Chapter Seventeen). Regardless of whether or not you understood the weakness of
the statistic, you should have been skeptical of the reference to juvenile turtles travelling 10,000
kilometers. Such a lengthy trip by a juvenile animal (which is not as strong as a mature animal) is
unlikely, and calls into question the soundness of the argument.

Answer choice (A): This answer does not impact the argument because no details—DNA or
otherwise— are given about the turtles at these nesting sites off the Pacific coast of North America.

Answer choice (B): The fact that Atlantic turtles have nesting and feeding sites no more than 5,000
kilometers apart does not attack the argument because the argument is about Baja turtles.

Answer choice (C): This answer attempts to weaken the argument by inducing you to conclude that
if the Japanese hatchlings are declining but Baja sites are constant, then the Baja sites cannot be
supplied by the Japanese hatchlings. But, the answer choice moves from the number of hatchlings to
the number of sites. Even with a declining number of hatchlings, the number of sites could remain
constant, albeit with fewer turtles at each. Because of this possibility, the answer does not undermine
the argument.

Answer choice (D): This is the correct answer. If 95 percent of the Baja samples match Atlantic
samples, this shows that the 95 percent result in the stimulus is not indicative of origin, and thus the
Baja turtles did not have to take the 10,000 kilometer trip.

Answer choice (E): The breeding between species was not an issue in the stimulus.

[moshei24]

Hi, why is answer (D) the correct answer?

Is it because the fact that 95% of the DNA from Baja turtle also match the DNA of Atlantic turtles, it weakens the idea that the match with the Japanese turtles is because they hatch there? But instead, it's probably some other reason, if Atlantic turtles, also have the same DNA? Like, it could just be something about turtles, in general, because the Pacific ones can't get to the Atlantic to breed there?

Can you clarify this for me, please?

Thanks!

[Adam Tyson]

Hey Moshei, you about ready to knock this one out of the park? Hope so - you've been working hard for a while now.

Your initial instincts were right on - the argument was based on the idea that a 95% DNA match between Pacific loggerheads and Japanese nesting sites meant the turtles hatched in Japan. Answer D says that same DNA match exists with Atlantic loggerheads, which probably could not have hatched in Japan. That means that a DNA match does not guarantee, or even strongly suggest, a hatching location, and so it does weaken the argument substantially.

Trust your instincts, young jedi! You should be about ready to crush the test by now.

Adam

[moshei24]

Thank you!

This time around I took it easy and kept my studying to very little. After I finish going over this test, my studying is done until Monday. And then on Monday, I'm going to try to care as little as possible about the test to keep my stress levels down and then I shall own the exam. That is all.

[DlarehAtsok]

I get why D) is right, but I do not understand the explanation in the 2015 Bible regarding C). To me C) is wrong because the conclusion does not mention anything regarding the number of loggerheads that feed in Baja, so whether or not the number is declining in Japan and being constant in Baja seems out of scope. Yet, in the Bible, the C) is marked wrong because the answer suggests that the number of nests, not of hatchlings, has remained constant (which according to the Bible leaves open the possibility that the number of hatchlings may go down). To me, if the conclusion mentioned anything about the number this answer would have weakened the argument, even referring to nests, because as you suggest a weaken answer does not have to eradicate the argument beyond any reasonable doubt, rather raise questions regarding its logical consistency, right? Thanks!

[Adam Tyson]

Good question, DlarehAtsok - let's see if I can shed a little light on that for you!

Your "out of scope" analysis and the explanation in the LR Bible are in perfect harmony with each other. The numbers are not, as you say, mentioned in the stimulus, but consider what effect it would have if the number of hatchlings in Japan were to go down while the number of juvenile turtles in Baja were to remain the same. How could those turtles in Baja have come from Japan if there are more of them than were hatched there? Wouldn't a lower rate of hatchlings lead to fewer turtles on the Baja beaches eventually? I suppose it's possible that the two things might be compatible - we could play with numbers a bit, maybe something to do with survival rates after hatching but before reaching Baja improving even while the number of hatchlings declines. But still, that odd information about the numbers would at least give you pause to wonder why the Baja turlte population hadn't decreased, and whether the Baja turtles were perhaps coming from somewhere else, wouldn't it?

Answer C's problem is not about numbers, but about focusing on counting the wrong things - the nests, rather than the turtles themselves. Fewer turtles doesn't have to mean fewer nests, because the nests could be less crowded than they were, or some nests are being left unused. Because the number of nests tells us nothing about the number of turtles, we can reject answer C. The nest numbers do nothing to impact the argument, even though the number of turtles might.

How does that match with your approach? Because nest numbers are simply "out of scope"! We tend not to explain things with that phrase very often, because it sheds so little light on the subject. Why is it out of scope, what is considered in scope, what the heck is this scope thing anyway - these are the sort of questions raised whenever we talk about something being "out of scope". We find that providing more depth and detail in our answers is the wiser, better approach, and it leads to greater understanding and, importantly, a greater ability to apply the lessons learned from one question to many other questions. Next time it won't be about turtles, but about shoes or ships or sealing waxes, or something else entirely, but answers about numbers, whether good answers or losers, will still need to be analyzed and evaluated.

Good job for getting the right answer, and for a perfectly good reason! Take another look at our explanation to see that it is just expanding on, and not contradicting, your approach. Keep up the good work!

[Shedrickc]

Hi, I think I finally understand the problem after reviewing a few explanations and I think I figured out my problem, but i wanted to make sure I was analyzing the stimulus correctly for future reference. We're told read the stimulus carefully and not to import outside info. But I feel like this question requires one to make what could be a dangerous assumption. I was attempting to keep track of the fact set to determine the linkage and it came down to an antecedent basis issue- "the Baja Turtles". I read "loggerhead turtles" and "pacific loggerheads" and that the "pacific loggerheads ...feed near the baja". So the assumption is that the Baja turtles are the "pacific loggerheads"...that feed near the Baja ? Once I could make the linkage the question made more sense and appeared pretty simple, but my frustration is that the LSAT questions in general require one to read carefully and not import info. This question down to the explanation appeared to make certain leaps even in the explanation that " you should have been skeptical of the reference to juvenile turtles traveling 10,000 miles" on page 274 of the logical reasoning bible. Why should I care that the baby turtles could've been born with super powers ?!?! Am I over analyzing, analyzing incorrectly, or all of the above. Can you please rephrase the question analysis -premise, conclusion so that i may better understand questions that are structured in this manner ? Although, i think i understand my error I'm not sure that I won't fall into the same trap again.

[Jeremy Press]

Hi Shedrick,

You're on the right track, especially with your reading of the stimulus. The key to making the link between "Baja turtles" in the last sentence of the stimulus (which is the premise for the conclusion) and "juvenile Pacific loggerheads that feed near the Baja peninsula" in the second sentence of the stimulus (which is the conclusion) is the tiny little word "the" in the third sentence. That "the" is referring to a specific set of turtles that must've already been mentioned in the argument. The only sensible referent for that "the" is the "Baja-associated" turtles mentioned in the second sentence. Making that connection is not what I would call an unwarranted, or even a questionable, assumption. That's simply following the normal grammatical rules under which we'd typically read a subsequent reference to a definite group as referring to the prior natural reference to that group.

Your issue with the LRB explanation is interesting, though keep in mind that we're not requiring you to make any strong assumption that such a 10,000 km journey couldn't have happened. What we want you to do (especially once you see the Weaken question stem) is simply to be skeptical of everything an argument tells you. Noticing the oddity of the journey implied by the stimulus isn't strictly necessary to getting the question right: I didn't really think about it the first time I did the question! But the LRB is right that it's a helpful step in "raising your Spidey sense" about potential problems in the argument. Be skeptical that the Baja loggerheads came from Japan! That will open you up to other possibilities (like, maybe they came from the Atlantic instead!).

I hope this helps!

Jeremy

[rk510]

While analyzing stimulus, I analyzed the last sentence as "if 1000 turtles samples were taken at Baja and at Japan, 950 had same DNA". It leads me to conclude that Pacific turtle at Baja and Pacific turtle at Japan are the same basis same DNA of 95% of the samples. While i understand, identifying the same 1000 samples would be close to impossible, what i wanted to point out was that the language is structured in such a manner that it leads us to conclude what I am concluding and not that there was a 95% DNA match between Baja turtle and Japanese turtle. Where am I going wrong? Please help.

[Paul Marsh]

Hi rk510! I see what you mean - it's possible the conclusion could be read that way. It might be that the test-takers are assuming some knowledge of DNA on the part of the test-taker (no two living organisms have the exact "same" DNA except for sometimes identical twins, which means that way of reading the conclusion doesn't make sense).

In any case - even if you read the conclusion your way, Answer Choice (D) remains the best answer choice. (D) still weakens the reasoning in the stimulus. It introduces new evidence showing that (by your way of reading it) 950 of the 1000 Baja turtles had identical DNA to Atlantic turtles. This shows that the "95% match" fact in the stimulus is very weak evidence for the stimulus's conclusion that the Baja turtles were born in Japan, since the new evidence in (D) makes it just as likely that the Baja turtles were born in the Atlantic!

So to sum-up, your reading makes lexical sense but not practical sense. But even if you do read it your way, (D) is still the best answer.

Hope that helps!