Logical Reasoning

PT119 · S3 · Q26 Fossilized teeth of an extinct

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Fossilized teeth of an extinct species of herbivorous great ape have on them phytoliths, which are microscopic petrified remains of plants.

Conclusion (must have)

The apes' diet consisted only of certain plants.

Evidence (since)

We only found the phytoliths of those certain plants on the apes' fossilized teeth.

Evaluate

This argument seems to think that the apes' fossilized teeth preserve a perfect and complete record of the apes' diet.

Maybe the ape ate plants A, B, C, and D, but only plants A, B, and C leave phytoliths on apes' teeth.

This author thinks that since all we see are phytoliths from plants A, B, and C, it must be that these apes only ate those three plants.

What if D was part of their diet but D just didn't survive the years as part of these fossilized remains?

Furthermore, what if the apes ate meat? Would that show up on their teeth? Oh, wait a sec. It said they were herbivorous, so we know they didn't eat meat.

Goal

In terms of the author's reasoning move, she's assuming these linking ideas:

If we didn't find it → it wasn't part of on their teeth their diet

If it was part of → we would see it on their diet their fossilized teeth

We could also see a Defender answer that is ruling out the objection we made: - There are not plants that the ape ate which do not leave phytoliths on fossilized teeth.

26.

The argument assumes which one of the following?

  1. None of the plant species

    Too Strong: none

    Would it matter to the author's argument if at least one of the plant species that left phytoliths no longer exists? Of course not. When the author sees that phytoliths from plants A, B, and C are found on the apes' fossilized teeth, she assumes that the apes ate plants A, B, and C, when the ape was still alive. But since this ape has gone extinct, it may have lived a long time ago and so it's perfectly plausible that some of the plants the ape ate have also gone extinct in the meantime.

    3% picked this

  2. Correct

    Plants of every type eaten

    Why this is right

    Conditionally, this would look like this: If ape ate plant → phytolith of plant X of type X would be left on their teeth The contrapositive of this rule will feel a lot like the author's reasoning move: If phytolith of plant X → then ape didn't isn't on their teeth eat plant X Alternatively, we could assess that this answer works by negating it and seeing that it turns into an objection. NEGATION: some of the plants eaten by the apes did not leave phytoliths on their teeth. That would be a big objection to the author's reasoning. That would allow us to argue that the apes' diet included some plants that were found on their teeth.

    Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

    75% picked this

  3. Each of the teeth examined

    Too Strong: each / same / all

    This is an extreme idea that every single tooth had the full suite of phytoliths. The author doesn't need that to be true. Say that the only phytoliths we found were from plants A, B, and C (so the author assumes that the apes only ate plants A, B, and C). Does it need to be true that on the apes' molars, there was A/B/C, and on the apes' incisors there was A/B/C? Or would the argument still work if we found A/B on the molars and C on the incisors? It would work either way. In either case, the author could surmise that the ape was definitely eating A, B, and C. (it might chew different plants with different parts of its mouth, and so it might not be that all plants show up on all teeth). Since the negation doesn't weaken, it can't be a necessary assumptino.

    18% picked this

  4. Phytoliths have also been found

    Out of Scope: other extinct apes

    This argument is only about one extinct species of herbivorous great ape. The author doesn't need to assume anything about any other species on Earth.

    3% picked this

  5. Most species of great ape

    Too Strong

    Too Strong: most Out of Scope: apes today This argument is only about one extinct species of herbivorous great ape. The author doesn't need to assume anything about modern apes. And the threshold of at least 51% is not important to this (or almost any) argument. The word "most" is wrong 99% of the time that we see it on Necessary Assumption.

    1% picked this

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