A recent study concludes that prehistoric birds, unlike modern birds, were cold-blooded. ████ ██████████ █ ██████ ████ ████ ████ ██████ █████ █████████ ████ ████████████ ██████ ███ ██████████ ██ █████ ██ ███ █████████ ██ ██████ █████ ██ ███████████ ██████ ██████ ███████████ █████ ███ ███████ ██ ██ █████ ████ ██ ████████████ ████████ ███████ ██████ ████████ ████████ ████ █████ ██ █████████ ████ ███████████ █████ ███ █████ █████ ███████ ██ █████ ██████ █████ ████████ ████ ████ ████ ██████ █████████ ███ █████████ ███ ██ ██ █████████████
Although the stem is uniquely phrased, this is just a Resolve question with two allowable templates for the right answer:
- How could it be that prehistoric birds seem so cold-blooded when they were really warm-blooded?
- How could it be that prehistoric birds seem so warm-blooded when they were really cold-blooded?
These birds have both growth rings and dense blood vessels. It is thought that only cold-blooded animals have growth rings and only warm-blooded animals have dense blood vessels, but those two statements can’t both be true.
We need an answer choice that tells us which one is false. Something like:
- Some warm-blooded animals actually do have growth rings.
- Some cold-blooded animals actually do have dense blood vessels.
Which one of the following, ██ █████ █████ ████ ████ ██ ███████ ███ ███████ █████████ █████ ██ █████ ██ ███ █████ ██ ███
Some modern warm-blooded ███████ █████ ████ █████ ████ ████ █████ ██ ████ █████████ ████ ████████████ ████████
This tells us it’s possible for a warm-blooded species to evolve from a cold-blooded species, but it doesn’t resolve the question at hand here, which is whether in fact prehistoric birds were warm- or cold-blooded.
We need an answer that points to “prehistoric birds were warm-/cold-blooded.” (A) says “it’s possible they were cold-blooded,” which is something we already knew (because we had direct evidence of their cold-bloodedness via growth rings).
Having growth rings ██ ███ ███ ████ ████████ █████ ██ ████████████ ████████
(B) says that there are other characteristics of cold-blooded species aside from growth rings, but it doesn’t tell us what those characteristics are or whether prehistoric birds had those characteristics.
(B) would be much better if it said “here are three more characteristics of cold-blooded species, and prehistoric birds had them all.” Or the opposite – “here are three; prehistoric birds had none of them.”
Modern birds did ███ ██████ ████ ███████████ ███████ ██ ██████
The stem asks us to resolve the debate in favor of one party – (C) resolves the debate by saying “you’re both wrong.”
We’re asking “did modern birds descend from cold-blooded or warm-blooded prehistoric birds?” We need an answer choice that picks one of those sides. (C) just comes in and says “NO”.
Dense blood vessels ███ ███ █████ ██ ███ ████████████ ████████
(D) is understandably tempting – it’s only wrong because it confuses sufficiency and necessity.
Team “prehistoric birds were warm-blooded” relies on the following principle:
If something has dense blood vessels, it must be warm-blooded.
Dense Blood Vessels → Warm-Blooded
To challenge that principle, we can say “not everything with dense blood vessels is warm-blooded” or “some things with dense blood vessels are cold-blooded.”
But (D) doesn’t say that – it’s either upside-down or backward, depending on how you think about it. It says “not everything that is warm-blooded has dense blood vessels” or “some things with no dense blood vessels are warm-blooded.”
I know that’s hard to follow, so here’s an analogy. If I give you the principle “all cats are cute,” you can challenge me by saying “some cats are not cute.” In this analogy, (D) says “some non-cats are cute.” Like “here’s a cute dog – boom you’ve been refuted.”
In some cold-blooded ███████ ███ ████ ████ ██ ███████████ ███ ██████ █████ ██ ████ ███████████ ███ █████ █████ ████████
(E) gives us a resolution to the “were prehistoric birds warm- or cold-blooded?” debate in favor of team cold-blooded. It undermines team warm-blooded’s line of reasoning by showing that dense blood vessels aren’t only found in warm-blooded species.
They thought “Dense blood vessels? Oh 100% slam dunk must be warm-blooded.” But that’s not true anymore, since sometimes cold-blooded species have them too.
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