PrepTest 144, Section 4, Question 25
Many bird and reptile species use hissing as(55 more words not shown)
Which one of the following,(13 more words not shown)
- ALike its potential(19 more words not shown)
- BThe common ancestor(15 more words not shown)
- CThe production of(19 more words not shown)
- DThe use of(25 more words not shown)
- EUnlike most modern(15 more words not shown)
Reading the argument
Why hiss at a predator that can't hear the sound?
Modern birds and reptiles use hissing as a threat. The similar way they produce it suggests the behavior goes back to a common ancestor. But the predators around at that earlier time lacked the anatomy needed to hear hissing.
Maybe the behavior originally served another purpose. Perhaps these animals used it to communicate with one another, and its role as a warning to predators came later. That's a possibility to investigate, not something the passage establishes.
What we’re looking for
The discrepancy question asks us to explain how the behavior could make sense in that earlier setting. I'd look for a useful function it could have had even when predators couldn't hear the hiss. We can keep the facts about modern threats and ancient hearing limits without assuming that the sound always worked in exactly the same way.
Working the answers
- A
This says the common ancestor also couldn't hear hissing. That would make our communication guess less promising, but it wouldn't explain why the behavior occurred. Removing another possible listener doesn't supply a function for producing the hiss.
- B
Other threat devices could protect the animal, but what was hissing doing? Knowing it had several defenses doesn't explain the usefulness of this particular behavior when its predators couldn't hear the sound.
- CCorrect
Producing the hiss made the animal look bigger. A predator could see that increased apparent size even if it couldn't hear the accompanying sound. So the behavior could still deter a predator through its visible effect. This takes a different route from our communication guess: the benefit could remain a threat to predators, with the noise accompanying a display that mattered for another reason.
- D
A behavior being cheap in energy doesn't tell us what good it does. If predators couldn't hear the hiss, we still need to explain how producing it helped. Spending little energy on an unexplained behavior doesn't resolve the discrepancy.
- E
Having few predators doesn't explain why hissing would work against any of them. Those predators still couldn't hear it. The number of threats changes, but the missing connection between the behavior and a useful effect remains.
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