Self-study
P1
The pronghorn, an antelope-like mammal that lives on the western plains of North America, is the continent's fastest land animal, capable of running 90 kilometers per hour and of doing so for several kilometers. ███
Intro Topic ·
Pronghorn
Puzzling Phenomenon ·
Pronghorns' speed
Why are they faster than they need to be to escape any predator?
Biologist: Explanation ·
Speed was adapted for extinct predators
P2
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Others: SKEPTICAL ·
Others skeptical of relict behavior hypothesis
Relict behavior defined as behavior adapted to extinct conditions, e.g., extinct predators.
Others: Elaboration ·
Skeptical of hypothesis because difficult to test
Extinct conditions (e.g., predators) means no longer exist, so how can you test?
Support Biologist ·
Some evidence supporting general relict behavior hypothesis
But what about for pronghorns, specifically?
P3
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Support Biologist ·
Lots of evidence for pronghorn relict behavior hypothesis
Examples ·
Roam in herds, choose faster mates
Both behaviors once conferred evolutionary advantage but no longer do. Yet we still observe this relict behavior.
P4
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Support Biologist ·
Relict behavior in other animals
Examples ·
Stickleback, ground squirrels
Both exhibit relict behavior: they avoid extinct predators.
Elaboration ·
Relict behavior can disappear over time
Arctic squirrel lost extinct predator avoidance behavior after 3m years.
Passage Style
Phenomenon-hypothesis (RC)
Single position
17.
Based on the passage, the ████ █
a
behavior that persists ████ ██████ ███ ██████████ ████ ████████ ███ ████████████ ███████ ███ ███████
The “principal component” is something that’s extinct. But “behavior that persists” is behavior that continues...so it’s not extinct. That’s why (A) doesn’t make sense as the meaning of “principal component.”
b
the original organism █████ ████████████ ████████ ██ █████ ████████████ ██ ██████ ████████
As explained below the question stem, the “principal component” refers to the environmental conditions that are extinct, but that caused evolutionary adaptation of the behavior that we see today. Nothing in the passage suggests that the phrase refers to the original animal from which the animal whose relict behavior we are examining descended. (For example, the evolutionary ancestor of the pronghorn. Do biologists believe it’s difficult to test the relict behavior hypothesis for the pronghorn because the ancestor of the pronghorn no longer exists? No.)
c
the pronghorn's ability ██ ███ ██ ██████████ ███ ████ ████ ████ █████████
The “principal component” is something that’s extinct. The pronghorn’s ability to run fast is something that exists today. So it doesn’t make sense for “principal component” to refer to the pronghorn’s running speed.
d
the environmental conditions ██ ████████ ██ █████ ██████ █████████ ███ ███████ ██ ████ █████████
This best captures the meaning of “principal component” for the reasons explained below the question stem.
e
an original behavior ██ ██ ██████ ██ █████ ███████ ███████████ █████████ ███ ███████ ██ ██ █████████████
Explanations based on relict behavior don’t involve changes to original behaviors. In fact, they involve behavior that