People who live unusually long tend to have been lean young adults who

AjiteshArun

The passage starts by people who live "unusually" long so we are therefore talking about a group of people that is definitely not the majority. This minor population group has a tendency X --> they used to be lean young adults who went on to gain approximately one pound every year.
In the second part of paragraph we are talking lean adults in the overall population, so this is a bigger group as it includes both young adults who would potentially go on to live longer and those who won't. Now we are factoring in the tendency X, from a sub (minor) group, to say that all the lean young adults should comply with tendency X in order to achieve a longer age. Isn't that what option E is saying?

Hi Namangupta1997,

Let's take a statement similar to the author's:

1. People who become CEOs of big tech companies tend to be Indians with engineering degrees. So Indians can improve their chances of becoming the CEO of a big tech company by getting an engineering degree. ← Subgroup = people who become CEOs of big tech companies, tendency = Indians w/ engineering degrees, and population = all people in the set.

What's the flaw here? An option equivalent to E would tell us that the problem with the argument is that the entire population doesn't necessarily have the tendency that the subgroup has. But that's not the problem here. In fact, the author isn't even looking at the population as a whole. So "the population as a whole doesn't share the tendency of CEOs of big tech companies to be Indians with engineering degrees" isn't a flaw in an argument that concludes that "Indians can improve their chances of becoming the CEO of a big tech company by getting an engineering degree". The real problem is that the author assumes that an {engineering degree} (for an Indian) leads to {CEO of big tech company}.

Similarly, in this question, the author doesn't say anything about the entire population, so the fact that the population as a whole doesn't necessarily share the tendency of the subgroup to have been lean young adults who gained ~1 pound every year doesn't point to a flaw in the author's reasoning. Even if the population as a whole doesn't necessarily have that tendency, lean young adults may improve their chances of living a long life by gaining ~1 every year.

People who live unusually long tend to have been lean young adults who went on to gain approximately one pound every year, so lean young adults can improve their chances of living a long life by gaining about a pound every year.

Understanding the argument (leaving the argument on the top to avoid back and forth) -
People who live long (this encompasses practically everyone who lives long) > tend to be lean young adults who gain approx. one pound every year. (there is a correlation. Is there any causation mentioned here? No. Just plain fact and some correlation between two facts). It's kind of some argument such as the car accident rate going down and, at the same time, the liquor sales going down. We are just starting with two plain facts that have a positive correlation. But do we know one caused the other - we don't know yet.

Now, the conclusion followed by the word "so" says that lean young adults, by gaining one pound every year > can improve their chances of living a long life. Now it's saying that "gaining one pound every year" is the cause of improved chances of living. For whom? For the lean young adults.
If our example concludes that - so lower liquor sales lead to lower accident rates. So what are we doing? We have just taken two different facts that were somehow positively correlated and turned that correlation into a cause and effect. This is a classic "causation flaw."

Option Elimination -

(A) gives reasons for the truth of its conclusion that presuppose the truth of that conclusion - A lot to unpeel here. Let's, for the sake of simplicity, ditch the modifiers and look at the core of this option. It says, "The argument gives reasons that presuppose the truth of that conclusion." In plain English, it means that the premises (reasons) assume (presupposes) the conclusion is already true (the truth of the conclusion)." This is called circular reasoning. What is that? Let me share an example - The book is valuable because it's worth a lot of money.
The conclusion is "the book is valuable," and the supporting premise is "it's worth a lot of money." If you look here, the premise is nothing, but the conclusion is stated using different words.

Is the argument given anything like the circular argument? Okay let's see what a circular argument will look like for our argument -
People who live long tend to be lean young adults who gain approximately one pound every year because those who live a long time are generally lean young adults who gain about a pound annually.

Is our conclusion like this circular argument - No. Option A is out. Moreover, from our rethinking, we know it's a causal flaw argument wherein we have just taken two different facts that were somehow positively correlated and turned that correlation into a cause and effect.

(B) proceeds as though a condition that by itself is enough to guarantee a certain result must always be present for that result to be achieved - It says that a condition, i.e., gain one pound every year is sufficient for a certain result (live long) is a necessary condition for that result (live long) to be achieved. This option is confusing us with another common flaw error, i.e., necessary v.s. Sufficient condition.
E.g., Every student who studies diligently will excel in their exams. Here, we have a necessary condition to study diligently, but is studying diligently the only condition to excel in the exam? We may need attitude, good study material, effective strategies, and studying diligently. Studying diligently is not the only reason but the flaw in the argument it assumes it is the sufficient (enough) condition.

Does our argument present any sort of necessary vs sufficiency flaw? No. It's a causation flaw.

(C) assumes without proof that two phenomena that occur together share an underlying cause - Does the argument say that the two phenomena "People who live long (this encompasses practically everyone who lives long)" and "tend to be lean young adults who gain approx. one pound every year" - we have any underlying third cause causing both. No.

(D) concludes that one phenomenon is the cause of another when at most what has been established is an association between them - exactly as we discussed in our rethinking.

(E) fails to recognize that a tendency widely shared by a subgroup within a given population will not necessarily be widely shared by that population as a whole - this means that just because the lean young adults live long by gaining one pound a year is not applicable to the population as a whole (the classic representation flaw). But just hold on - is even the argument extrapolating it to the population as a whole? No. It just falsely states the causality between the positively correlated phenomena.