The top 50 centimeters of soil

Answer choices

1. A

   Strengthens3% picked this

   The bird species known to have been eaten by the islanders had few natural

   This indicates that bird species eaten by humans had few natural predators, implicitly ruling out an alternate explanation for why the birds dwindled in number and variety.

   3%
2. B

   Strengthens3% picked this

   Many of the bird species that disappeared from Tiliga did not disappear from other, similar, uninhabited

   This shows that similar birds persisted longer on uninhabited islands, suggesting a correlation between human presence and bird decline, reinforcing the causal link to humans. It's a No Cause, No Effect strengthener --- the islands that DIDN'T have humans arrive, DIDN'T have bird species disappearing.

   3%
3. C

   Correct86% picked this

   The arrival of a species of microbe, carried by some birds but deadly to many others, immediately preceded the

   Why this is right

   This introduces a microbe carried by some birds but deadly to others, which appeared just before humans arrived. It offers an alternate explanation for the bird decline unrelated to human activity, thus weakening the argument.

   Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

   86%
4. D

   Unclear Impact6% picked this

   Bones from bird species known to have been eaten by the islanders were found in the underlying

   If anything maybe this strengthens. It seems to be saying that some of the birds we know these islanders eat were on the island before humans arrived (since they show up in the older soil). If islanders are currently eating these birds, then those birds haven't gone extinct yet from the arrival of humans (but maybe they're on their way to going extinct).

   6%
5. E

   No Impact2% picked this

   The birds that lived on Tiliga prior to the first human immigration generally did

   This notes that birds prior to humans didn’t fly well but doesn’t explain their decline or introduce a factor that distinguishes pre-human and post-human periods in the bird population. If anything, this strengthens by making it more plausible that humans would be able to trap and kill these (non-flying) birds.

   2%