CR Bible | Weaken

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CR Bible | Weaken

by [email protected] » Thu Oct 13, 2016 6:09 am
Loggerhead turtles live and breed in distinct groups, of which some are in the Pacific Ocean and some are in the Atlantic. New evidence suggests that juvenile pacific loggerheads that feed near the Baja peninsula hatch in Japanese waters 10,000 kilometers away. Ninety-five percent of the DNA samples taken from the Baja turtles match those taken from turtles at the Japanese nesting sites.
Which one of the following, if true, most seriously weakens the reasoning above?

(A) Nesting sites of loggerhead turtles have been found off the Pacific coast of North America several thousand kilometers north of the Baja peninsula.
(B) The distance between nesting sites and feeding sites of Atlantic loggerhead turtles is less than 5,000 kilometers.
(C) Loggerhead hatchlings in Japanese waters have been declining in number for the last decade while the number of nesting sites near the Baja peninsula had remained constant.
(D) Ninety-five percent of the DNA samples taken from the Baja turtles match those taken from Atlantic loggerhead turtles.
(E) Commercial aquariums have been successfully breeding Atlantic loggerheads with Pacific loggerheads fro the last five years.

d
Source: — Critical Reasoning |

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by [email protected] » Thu Oct 13, 2016 6:12 am
Hi Experts,

I had a tough time with this question. Please through some light on the structure. I could not understand what is the conclusion and how the argument is organised.

Is the conclusion- Loggerhead turtles live and breed in distinct groups, of which some are in the Pacific Ocean and some are in the Atlantic.

Or is the conclusion - suggests that juvenile pacific loggerheads that feed near the Baja peninsula hatch in Japanese waters 10,000 kilometers away.

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by crackverbal » Mon Oct 17, 2016 1:11 am
None of those.

The line of reasoning employed is this -

95% DNA match --> Loggerhead turtles at Baja and at Japanese nesting sites are the same.

This immediately sounds problematic. Just a 95% DNA match does not mean the turtles at the two locations are the same. For example - humans and chimps share 98% of their DNA. Does not mean same species.

A - strengthens the argument. If they have nesting sites several thousand kilometers away from Baja, it is possible that they can have such sites in Japanese waters too.
B - we are discussing pacific loggerhead turtles. So, this option is not relevant.
C - does not mean that they do not nest in Japanese waters
D - Correct answer. this suggests that the turtles in Japanese waters need not necessarily come from Baja. It is possible that they might be a different species of turtle. After all, Atlantic and Pacific turtles share 95% of DNA.
E - not relevant to the argument at all.
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by [email protected] » Mon Oct 17, 2016 10:41 am
Hi Crackverbal,

Great explanation. Can you guide me how you extracted this line of reasoning. Because the conclusion wasn't explicitly stated, I want to know how to arrive at making such implicit connections? More in terms of what parts of the argument gave the conclusion away so that you know what to attack or weaken?