PT53.S1.Q09 - global surveys estimate

dreamlawschool

https://7sage.com/lsat_explanations/lsat-53-section-1-question-09/
I could really use some help on this one.

First, here's a quick breakdown of the stimulus:

P: Nesting female leatherbacks have declined by more than 2/3.
P: Any species whose population declines by more than 2/3 is in danger of extinction.
C: Leatherback turtles are in danger of extinction.

Even though I quickly realized the gap between nesting females and the entire population of leatherbacks, I still don't see how answer A passes the negation rule (that the correct answer choice to all necessary assumption questions must pass).

A says: "The decline in the population of nesting female leatherbacks is proportional to the decline in the leatherback population as a whole."

When I negate answer choice A, I read it as "the decline in the population of nesting female leatherbacks IS NOT proportional to the decline in the leatherback population as a whole." While I see how this can be problematic for the conclusion, it doesn't necessarily make it false. Let's assume that the decline being referred to in the stimulus in the nesting female subpopulation is 70% (greater than 2/3). If we are applying the negation of A, then decline in the entire population of leatherbacks is NOT PROPORTIONAL to the 70% decline in nesting females. However, it still can be true that the entire population of leatherback turtles is declining by more than 2/3 (they're declining by 85%). So the conclusion can still be true that leatherbacks as a whole are in danger of extinction.

So while A would be the perfect sufficient assumption answer choice, it doesn't seem like it's playing by the LSAT's rules for necessary assumption questions.

Recognizing this problem, during blind review I chose answer choice D, because I assumed that "nesting" meant not living in captivity. So by negating D, it reads "Not very few leatherback turtles exist in captivity." And since "few" = "some, but not most," in plain English, D translates to: either none or most (>50%) of the turtleback population lives in captivity. So if most of these turtles do in fact live in captivity (let's just assume 51% of them do), then a 2/3 decline in the nesting females can constitute only a maximum overall decline of ~34% in the entire population of leatherbacks, which is obviously less than 2/3, and means we cannot make the conclusion that they're in danger of extinction. So isn't this assumption the necessary one?

Please help. My brain hurts...

runiggyrun

A giveaway for D not being the right answer is the use of "very few" as a qualifier. Even "a few" would be problematic, because the negation "either no turtles or a lot of turtles exist in captivity" leaves open the possibility of "no turtles", which doesn't undermine the conclusion. You can't pick and choose which part of the negation you want to use. "Very few" is even less clearly negated, and LSAT writers wouldn't use such vague language for a correct answer.
The detail that makes A right is that while it doesn't necessarily destroy the conclusion "the leatherback turtle is in danger of extinction", it does destroy the conclusion "the leatherback turtle is clearly in danger of extinction". They may or may not be, but if the decline in the population doesn't track the decline in nesting females we can't use the latter to conclude that they are clearly in danger.

Matt Dare

Hi. I approach NA by putting the whole argument in parentheses and then making that the SA. JY does this in an early NA lesson. Anyway, if turtles are in danger of extinction because a survey found that nesting females have declined by 2/3 in 15 years then ____________. Slap each answer choice into that and evaluate. Below I paraphrase the entire thing as blah blah blah.

For C: if the survey results are not representative of the population then a conclusion about the population based on said survey may not represent the population. In other words for the conclusion to be valid the survey MUST be representative of the entire population. It's absolutely necessary. If blah blah blah then the decline of nesting females is proportional to the decline of the entire species. That works and works well. Negate the whole thing and the argument falls apart.

Regarding it looks likes your analysis of the negation of "few" omitted the possibility that no turtles live in captivity. Negate few that way, no turtles live in captivity, and it strengthens the argument considerably. Negate it the other way, the way you went with, that most turtles live in captivity, and it weakens the argument considerably. Putting it in the equation: if blah blah blah then very few turtles live in captivity. Since you can negate it two ways and those ways conflict D isn't necessary.