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passage 3
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
Single position
20.
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a
fossils of extinct ███████ ████████ ██ ████ ████ ████ ██ ███ ████ █ █████████
b
the absence of ██████████ ██ ███ ███████████ ███████████ ███████████
c
the present-day preference ██ ██████████ ███ ████████ █████
d
the apparent need ███ █ ███████ ███████████ ██ ███████ ███ ███ ███████ ████████ ██████████ ███ ███████
e
the occurrence of ██████ ████████ ██ █████ ███████