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The researchers claim: High BP in westernized Blacks = genes adapted to salt scarcity × high salt western diet
This is a TWO-FACTOR interaction. You need BOTH for high BP.

To strengthen an interaction hypothesis, show what happens when you REMOVE one factor.

The best evidence would show:
  • Remove the genes (but keep high salt diet) → no high BP, OR
  • Remove the high salt diet (but keep the genes) → no high BP

This proves both factors are necessary.
The novel claim here is the GENETIC component - that's what makes this interesting. Everyone already knows high salt causes high BP generally. The researchers are saying certain genes make people MORE susceptible.

So the strongest evidence would test: Do you need these specific genes for the problem to occur?

(A) Blood pressures are low among those from Senegal/Gambia, where salt was always available ✓

What this tells us:

  • NO salt-scarce genes (ancestors always had salt available)
  • Westernized Black Africans (stated in question) = high salt western diet
  • Result: Low BP

Why this strengthens:
  • Removes the GENE factor
  • Keeps the DIET factor (high salt)
  • No high BP occurs
  • This proves you NEED the salt-scarce genes for high BP

This directly tests whether the genetic component is necessary - which is the novel part of the hypothesis.

(D) Blood pressures are low among the Yoruba, who have been far from salt sources

What this tells us:
  • Salt-scarce genes (ancestors far from salt)
  • Low BP today
  • Current diet: Unknown

Your reasoning: "They probably eat low salt, so this shows removing high salt removes high BP."

Why this is weaker than A:
Even if we assume they eat low salt (we aren't told anything about their current diet, just the historic diet, but even if we assume this), this just confirms "less salt = less BP" - which we already know. High salt causing high BP is not news.
The hypothesis's interesting claim is about the GENETIC susceptibility. D doesn't test whether the genes are necessary - it just shows that without high salt intake, BP stays low. But that's true for everyone, regardless of genes.

D doesn't isolate and test the genetic component like A does.

Both A and D show removing one factor removes the high BP problem.

But A is stronger because:
  • A tests the GENETIC component (the novel claim)
  • D may test the DIET component (which we already know matters for everyone, but again, we don't know their diet)

kabirgandhi
Hi MartyMurray, GMATNinja, WhitEngagePrep

Could someone help to understand this solution better?

Conclusion: High BP among westernised African people (black Americans and westernised black Africans) has been caused by the interaction of their genes (conditioned to salt scarcity) and high salt western diets. Essentially, we are asked to strengthen: High WA BP = Low salt genes x High Salt Diet


Anything that removes the cause, such that the effect is removed as well, would strengthen the cause-and-effect relationship. For example, if there are some westernised/non-westernised Africans that do not eat high salt diets and have low BPs, it should ideally strengthen this.

I think choice D) does exactly that - it shows that some African people who are far away from salt do not have high BPs.

Whereas choica A) tells us that when the ancestors of some African people did not have salt scarcity, they did not have high BPs. Even though this, if anything, tries to challenge a premise: that is, some African people who did have salt, had low BPs, I think this weakens the argument, instead of strengthening it.
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egmat But still to make the option A correct you'll have to assume that residents of Senegal/Gambia are black not white! I mean ofcourse we know that those places are in Africa but again it was not stated in the argument.
egmat
The researchers claim: High BP in westernized Blacks = genes adapted to salt scarcity × high salt western diet
This is a TWO-FACTOR interaction. You need BOTH for high BP.

To strengthen an interaction hypothesis, show what happens when you REMOVE one factor.

The best evidence would show:
  • Remove the genes (but keep high salt diet) → no high BP, OR
  • Remove the high salt diet (but keep the genes) → no high BP

This proves both factors are necessary.
The novel claim here is the GENETIC component - that's what makes this interesting. Everyone already knows high salt causes high BP generally. The researchers are saying certain genes make people MORE susceptible.

So the strongest evidence would test: Do you need these specific genes for the problem to occur?

(A) Blood pressures are low among those from Senegal/Gambia, where salt was always available ✓

What this tells us:

  • NO salt-scarce genes (ancestors always had salt available)
  • Westernized Black Africans (stated in question) = high salt western diet
  • Result: Low BP

Why this strengthens:
  • Removes the GENE factor
  • Keeps the DIET factor (high salt)
  • No high BP occurs
  • This proves you NEED the salt-scarce genes for high BP

This directly tests whether the genetic component is necessary - which is the novel part of the hypothesis.

(D) Blood pressures are low among the Yoruba, who have been far from salt sources

What this tells us:
  • Salt-scarce genes (ancestors far from salt)
  • Low BP today
  • Current diet: Unknown

Your reasoning: "They probably eat low salt, so this shows removing high salt removes high BP."

Why this is weaker than A:
Even if we assume they eat low salt (we aren't told anything about their current diet, just the historic diet, but even if we assume this), this just confirms "less salt = less BP" - which we already know. High salt causing high BP is not news.
The hypothesis's interesting claim is about the GENETIC susceptibility. D doesn't test whether the genes are necessary - it just shows that without high salt intake, BP stays low. But that's true for everyone, regardless of genes.

D doesn't isolate and test the genetic component like A does.

Both A and D show removing one factor removes the high BP problem.

But A is stronger because:
  • A tests the GENETIC component (the novel claim)
  • D may test the DIET component (which we already know matters for everyone, but again, we don't know their diet)


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The hypothesis isn't about race causing high BP.

Look at what researchers actually claim: "genes that adapted to an environmental scarcity of salt."

The mechanism is:
  • Ancestors lived in salt-scarce environments → developed salt-conserving genes
  • These genes + western high-salt diet → high BP

Race (Black vs White) is just a proxy for observing this pattern. The actual causal mechanism is about salt-scarcity genes, not race itself.

thelastskybender
egmat But still to make the option A correct you'll have to assume that residents of Senegal/Gambia are black not white! I mean ofcourse we know that those places are in Africa but again it was not stated in the argument.

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egmat
The hypothesis isn't about race causing high BP.

Look at what researchers actually claim: "genes that adapted to an environmental scarcity of salt."

The mechanism is:
  • Ancestors lived in salt-scarce environments → developed salt-conserving genes
  • These genes + western high-salt diet → high BP

Race (Black vs White) is just a proxy for observing this pattern. The actual causal mechanism is about salt-scarcity genes, not race itself.


Even then option A rests on the assumption that those people were not having low salt intakes. I mean since there is an AND operator in the conclusion so we can't ignore the other case.
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There's no need to assume that people of Senegal/Gambia are black neither do we need to assume that all populations mentioned in any option eats western diet because its already mentioned in the question that "...following statements about present-day, westernized Black Africans, if true,..."

option A- inspite of western diet BP is low, historically salt available-> gene not present (one of two factors for interaction not available hence BP is not high) supports argument

option B and C are completely irrelevant

option D- Yoruba historically situated far from salt, probably has gene AND eats western diet- both factors for interaction present still low BP, goes against the conclusion. Hence weakens the argument

option E is also weakening as it goes against the Researchers' argument.
thelastskybender
egmat But still to make the option A correct you'll have to assume that residents of Senegal/Gambia are black not white! I mean ofcourse we know that those places are in Africa but again it was not stated in the argument.

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