Logical Reasoning

PT114 · S4 · Q15 Loggerhead turtles live and breed

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

Conclusion (evidence suggests that)

Juvenile Pacific loggerheads that feed near Baja hatch in Japanese waters 10,000 km away.

Evidence

Loggerheads live and breed in distinct groups, some in the Pacific and some in the Atlantic.

95% of the DNA samples of the Baja turtles match DNA samples taken from turtles at the Japanese nesting sites.

Evaluate

The author is trying to make sense of a Curious Fact: why do 95% of the DNA samples from the Baja population of loggerheads match DNA from the Japanese population of loggerheads?

Her Explanation is that loggerheads are being hatched (i.e. born) in Japan and then end up across the Pacific ocean (Baja peninsula is part of Mexico) by the time they're juveniles.

Goal

Since this is Weaken, we either need:

1. to suggest an Alternate Explanation for the curious fact (what could be a different causal storyline that would account for 95% of the DNA samples from Baja/Japan matching?)

or

2. to undermine the plausibility of the Author's Explanation (what could hurt the storyline that these loggerheads were born in Japan and then crossed the pacific ocean to feed in Mexico, by the time they're juveniles?)

15.

Which one of the following, if true, most seriously weakens the reasoning above?

  1. Nesting sites of loggerhead turtles

    No Impact

    This is tempting at first as a possible Alternate Explanation, as in "oh, these juveniles in Baja didn't come from Japan; they came from up the pacific coast in North America!" But we weren't trying to explain "where did these juveniles in Baja come from". We were trying to explain "how come 95% of the DNA samples from the Baja turtles match the DNA from the Japanese turtles?" This answer doesn't provide an alternate explanation for that.

    8% picked this

  2. The distance between nesting sites

    Less Impact than Correct Answer

    This definitely weakens the plausibility of the author's storyline a little. She's trying to sell us on a story in which the nesting site and feeding site of Pacific loggerheads are 10,000 km apart. If Atlantic loggerheads travel less than 5,000 km from nesting side to feeding site, it makes it a little suspicious that Pacific loggerheads would be willing to go more than twice as far. But since they are distinct species, it's possible that Pacific loggerheads are adapted to travel farther distances. So this impugns the author's story a bit, but since it's talking about a different, though related, species it's not a super strong challenge.

    9% picked this

  3. Loggerhead hatchlings in Japanese waters

    Unclear Impact

    This answer is talking about "nesting sites" near Baja, which we never talked about before. We were discussing turtles feeding in Baja but having hatched in a nest in Japan. There might be zero nesting sites near Baja. So if that number has remained constant at zero, that won't really tell us anything. If this answer said "hatchlings in Japan have been declining in number for the last decade while the number of loggerheads feeding near Baja has remained constant", then that would hurt the plausibility of the author's storyline. Since she is selling us on this "born in Japan, feed in Baja" pipeline, she would expect that a dwindling of turtles born in Japan would eventually manifest in a dwindling of turtles feeding in Baja.

    11% picked this

  4. Correct

    Ninety-five percent of the DNA

    Why this is right

    This supplies an alternate explanation for the DNA match. It's not, as the author thinks, because these juvenile loggerheads in Baja were born in Japan. Instead, it's just because loggerhead DNA is pretty similar wherever you go. If 95% of the DNA from the Baja group matches DNA from a group of Atlantic loggerhead turtles, would we come to the conclusion that the Baja juveniles originally hatched in the Atlantic? No, because we were told that Pacific loggerheads and Atlantic loggerheads are distinct groups. They live and breed separately from each other. So this answer presents us with a case where there's a 95% DNA match, even though we know that the Baja juveniles did not hatch in the Atlantic. Thus, it makes the author's evidence feel worthless. She's saying, "These Baja juveniles must have hatched in Japan, since there's a 95% DNA match with loggerheads from Japan." And this answer allows us to say, "a 95% DNA match with a certain population is not good evidence that juveniles came from that population. After all, Pacific juveniles at Baja have a 95% DNA match with a population of Atlantic loggerheads, and we know the Pacific juveniles didn't come from that population."

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

    66% picked this

  5. Commercial aquariums have been successfully

    No Impact

    The loggerheads we're analyzing are not cross-breeds and they don't live in an aquarium, so it doesn't seem like this answer has any relevance to the conversation at hand.

    6% picked this

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