In Strengthen (and Weaken, and Evaluate) questions, the stem tells us to expect an argument that is vulnerable to criticism in some way. We therefore approach the stimulus with a critical eye, looking for unreasonable assumptions and faulty reasoning methods – weak points which can either be exploited (Weaken), bolstered (Strengthen), or questioned (Evaluate) by a critical reader.

Far and away the most common criticizable argument structure on display in these questions involves a type of causal reasoning we call “phenomenon-hypothesis”: the premises lay out some observations about the world (e.g. “I saw a bunch of birds flying south.”) and the conclusion offers a potential explanation for that phenomenon (e.g. “They must be fleeing a hoard of bird-eating godzillas.”)

This pattern is so common in these questions that “Am I in a phenomenon hypothesis world?” should be an explicit consideration in your mind as you approach the stimulus. Whenever you see it, the broad approach to anticipating the answer is similar: brainstorm some alternate explanations for the phenomenon (“maybe they’re just flying south because winter is coming”), and poke holes in the explanation presented to you (“there’s no such thing as bird-eating godzillas”).

Then, in Strengthen questions in particular, we take the additional step of repairing those vulnerabilities: correct answers will eliminate alternative explanations or plug holes in the explanation the argument offers.

Right off the bat, “A recent study” should make you suspect we’re in phenomenon hypothesis land. We’re gonna learn some observed facts from the study, and expect a causal conclusion pitching us on an explanation of those facts. And indeed that’s what happens in this stimulus:

There are two subspecies of chimps: East ones and West ones. Within these subspecies, there are different chimp groups – some East groups and some West groups. We watched these chimps groom each other and forage around for a while, and it turns out different groups have different styles.

In particular, one of the East groups did a lot of West-style grooming and foraging. That’s interesting. We think this suggests that grooming and foraging styles are probably cultural AND probably not genetic.

Analyzing this argument requires knowing that species are defined genetically. Different subspecies are genetically distinct, and animals within the same subspecies are genetically similar – that’s how we scientists do things.

Anyway, our conclusion really makes two related claims: our explanation is right, and this other explanation is wrong. This gives our anticipation a bit more focus: it’s likely that our correct answer choice will bolster the cultural explanation in a way that undermines the genetic explanation.