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20 Nov 2025, 03:13
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
81% (01:44) correct
19%
(02:29)
wrong
based on 148
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When the ancient fossils of a primitive land mammal were unearthed in New Zealand, they provided the first concrete evidence that the island country had once had indigenous land mammals. Until that discovery, New Zealand had no known native land mammals. The discovery thus falsifies the theory that New Zealand’s rich and varied native bird population owes its existence to the lack of competition from mammals.
Which one of the following, if true, most seriously weakens the argument?
(A) The unearthed land mammal is only one of several ancient land mammals that were indigenous to New Zealand.
(B) The recently discovered land mammal became extinct long before the native bird population was established.
(C) The site at which the primitive land mammal was unearthed also contains the fossils of primitive reptile and insect species.
(D) Countries with rich and varied native land mammal populations do not have rich and varied native bird populations.
(E) Some other island countries that are believed to have no native land mammals in fact had indigenous land mammals at one time.
Which one of the following, if true, most seriously weakens the argument?
(A) The unearthed land mammal is only one of several ancient land mammals that were indigenous to New Zealand.
(B) The recently discovered land mammal became extinct long before the native bird population was established.
(C) The site at which the primitive land mammal was unearthed also contains the fossils of primitive reptile and insect species.
(D) Countries with rich and varied native land mammal populations do not have rich and varied native bird populations.
(E) Some other island countries that are believed to have no native land mammals in fact had indigenous land mammals at one time.
msignatius
13 Dec 2025, 01:09
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The correct answer should be B.
The theory in the stem states that the presence of fossilized mammal remains in New Zealand nullifies the theory that today's vast variety of birds in the region is owed to an absence of mammal populations in the past. B weakens this claim, because at the time when the bird populations grew, the mammal had long been gone. A correlation / competition between birds and mammals is only possible if the two co-existed.
Why the other answers won't work:
A strengthens the claim, as the prevalence of more fossilized mammals remains in the area will further reinforce element of past competition between birds and mammals.
C is irrelevant. There's no debate involving reptiles and insect species. We deal with birds and mammals here.
D can be eliminated simply because the presence of rich and varied land mammal populations while bird population is low in certain countries, may simply be a coincidence. The fact that rich mammal populations = poor bird population, does not mean the former has caused the latter.
E is again irrelevant, as it primarily established that land mammals can go extinct - which does not add any valuable information.
The theory in the stem states that the presence of fossilized mammal remains in New Zealand nullifies the theory that today's vast variety of birds in the region is owed to an absence of mammal populations in the past. B weakens this claim, because at the time when the bird populations grew, the mammal had long been gone. A correlation / competition between birds and mammals is only possible if the two co-existed.
Why the other answers won't work:
A strengthens the claim, as the prevalence of more fossilized mammals remains in the area will further reinforce element of past competition between birds and mammals.
C is irrelevant. There's no debate involving reptiles and insect species. We deal with birds and mammals here.
D can be eliminated simply because the presence of rich and varied land mammal populations while bird population is low in certain countries, may simply be a coincidence. The fact that rich mammal populations = poor bird population, does not mean the former has caused the latter.
E is again irrelevant, as it primarily established that land mammals can go extinct - which does not add any valuable information.
13 Dec 2025, 04:37
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Explanation
New Zealand was thought to have no native land mammals. Now fossils of a primitive land mammal have been found there. This discovery falsifies the theory that New Zealand’s rich native bird population exists because of lack of competition from mammals.
Finding mammals seems to contradict “no mammals,” so the theory’s premise is wrong, and also theory is false.
Understand what would weaken the argument
To weaken: show that despite the discovery of this mammal, the lack of competition from mammals could still be the reason birds thrived.
One way: show the mammal didn’t actually compete with birds (e.g., lived at a different time, or wasn’t part of the relevant ecosystem when birds diversified).
(A) Says there were several ancient land mammals in NZ.
This strengthens the counterevidence against “no mammals,” making the argument stronger, not weaker.
(B) Says this mammal became extinct long before native bird population was established.
If true, then when birds diversified and thrived, there were no mammals competing with them so the “lack of competition” theory could still be true. Weakens.
(C) Mentions fossils of reptiles/insects at same site
This is irrelevant to mammal-bird competition theory.
(D) General claim about other countries
This is also not relevant to whether in NZ the discovered mammal competed with birds. At best, it might suggest mammal presence doesn’t preclude bird richness, but doesn’t directly address timing or competition in NZ’s history.
(E) About other islands
irrelevant to NZ’s specific situation.
If the mammal was extinct before birds established, then there was no mammal competition during birds’ establishment period — so the “lack of competition” theory could still be correct. This breaks the link between the evidence (mammal fossils found) and the conclusion (theory falsified).
Answer: B
New Zealand was thought to have no native land mammals. Now fossils of a primitive land mammal have been found there. This discovery falsifies the theory that New Zealand’s rich native bird population exists because of lack of competition from mammals.
Finding mammals seems to contradict “no mammals,” so the theory’s premise is wrong, and also theory is false.
Understand what would weaken the argument
To weaken: show that despite the discovery of this mammal, the lack of competition from mammals could still be the reason birds thrived.
One way: show the mammal didn’t actually compete with birds (e.g., lived at a different time, or wasn’t part of the relevant ecosystem when birds diversified).
(A) Says there were several ancient land mammals in NZ.
This strengthens the counterevidence against “no mammals,” making the argument stronger, not weaker.
(B) Says this mammal became extinct long before native bird population was established.
If true, then when birds diversified and thrived, there were no mammals competing with them so the “lack of competition” theory could still be true. Weakens.
(C) Mentions fossils of reptiles/insects at same site
This is irrelevant to mammal-bird competition theory.
(D) General claim about other countries
This is also not relevant to whether in NZ the discovered mammal competed with birds. At best, it might suggest mammal presence doesn’t preclude bird richness, but doesn’t directly address timing or competition in NZ’s history.
(E) About other islands
irrelevant to NZ’s specific situation.
If the mammal was extinct before birds established, then there was no mammal competition during birds’ establishment period — so the “lack of competition” theory could still be correct. This breaks the link between the evidence (mammal fossils found) and the conclusion (theory falsified).
Answer: B
