Logical reasoning PrepTest 119 · Section 3 · Question 26

Incorrect. Since the apes themselves have gone extinct, it doesn't matter to the argument if the plants did, as well.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Extinct great ape teeth have plant remains on them, but only certain species of plant. So these great apes ate only these species of plant.

Answer Anticipation:
The argument is using the presence of plant remains on teeth to draw a conclusion about what plants these extinct great apes ate.

That requires two assumptions.

First, it requires the assumption that the only way these remains could get on the apes' teeth is through eating them. Maybe they were left on the teeth during decomposition or fossilization, or maybe the apes used them to clean their teeth but then spit them out.

Second, since the conclusion is that the apes ate nothing other than the species of plant that left remains on their teeth, the argument assumes that all plants would leave such remains if eaten. If there are plants out there that don't leave phytoliths on the teeth after consumption, then they could make up a part of the great ape diet without showing up in this analysis.

Either assumption could show up in a correct answer, so let's stay flexible.

Answer Explanation:
The argument concludes that making a list of phytoliths found on the great ape teeth will give you a complete list of the species they ate ("only of those plants"). This assumes that all of the plants left behind phytoliths, and the argument establishes only that phytoliths are left by plants, not that they're left by all plants.

Key Takeaway:
Whenever something is used as a proxy for measuring something else, check that a direct connection between the two has been established. Here, phytoliths were used to determine the diet of apes. Without knowing if phytoliths only end up on teeth if eaten, and that all plants that are eaten leave them behind, the jump is unwarranted.

Incorrect. If the overall population had a few different species' phytoliths on them, then a tooth here or there missing one of them wouldn't undermine the conclusion—maybe that ape didn't like that type of plant!

Incorrect. The conclusion is about this specific species of great ape, so other species are out of scope.

Incorrect. Great apes could have evolved away from characteristics of their extinct ancestors, so there's no need to assume anything about modern apes.