PrepTest 153, Section 3, Question 10
Giant ground sloths began disappearing from the Americas(58 more words not shown)
Which one of the following,(11 more words not shown)
- AScientists have not(16 more words not shown)
- BSpecies of smaller(10 more words not shown)
- CTheir large size(12 more words not shown)
- DGiant ground sloths(17 more words not shown)
- EOne type of(18 more words not shown)
Reading the argument
The end of an ice age and the disappearance of the sloths happen around the same time. I can see why scientists would connect them. If conditions changed and the sloths couldn't adapt, that could explain their decline. The timing alone, though, doesn't establish that explanation.
Now we have another event near that time: humans arrived. Maybe the climate did it; maybe humans did something that harmed the sloths. I don't know which account is right just from those overlapping dates.
We're asked to support the newer belief about humans. One route would be evidence of what the humans did. Did they hunt the giant ground sloths? Did they bring a disease that affected them? Either could supply a way for human arrival to cause the disappearance.
What we’re looking for
A second route would be evidence against the old climate explanation. Perhaps these sloths had survived the end of an earlier ice age. That would make it harder to assume they simply couldn't handle such a change. I'd first expect evidence connecting humans to the losses, but either route could help separate two events that initially occurred together.
Working the answers
- A
This does not give us evidence that humans hunted the sloths to extinction. It tells us that such physical evidence hasn't been found. That absence doesn't prove hunting never happened—evidence can be missing—but it offers no support for the proposed hunting route.
- B
These are smaller, tree-dwelling sloths, not the giant ground sloths whose disappearance we need to explain. Perhaps their size, habitat, or exposure to humans made their experience different. The answer doesn't supply a comparison that separates human effects from climate effects for the extinct animals.
- C
Difficulty adapting fits the old explanation that changing conditions were a problem. It doesn't identify a harmful effect of humans. Being less adaptable doesn't prove what caused the extinction, but it certainly isn't the evidence for the new account we were seeking.
- D
More kinds of mammals disappearing around the same date would leave us with the same question: why then? Both the climate change and human arrival occurred near that time. Adding other disappearances doesn't tell us which event explains them, or the sloths' disappearance in particular.
- ECorrect
These islands separate the two events. The ice age ended, yet the sloths there survived. Humans arrived much later, and the sloths survived until that arrival. We are no longer looking only at a case where climate change and human arrival coincide.
This both makes the ice-age explanation less convincing for the island case and gives us a further connection between humans and disappearance. We still haven't identified exactly what humans did or proved the cause of every extinction. But this is the sort of comparison that makes the scientists' newer explanation more plausible.
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