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19 Feb 2026, 14:32
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Biologist: Early mammals spent most of their time in environments with low light levels, such as forests and burrows. As a result, mammals today are naturally adapted to dim lighting. Hence, regular exposure to bright artificial light is likely to interfere with maintaining proper sleep cycles.
Which of the following is an assumption the biologist’s argument requires?
A. Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles.
B. Exposure to artificial light affects the brain differently than exposure to natural light.
C. Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.
D. Early mammals had healthier sleep cycles than most mammals have today.
E. Bright artificial light typically exceeds the intensity of daylight in natural environments.
Which of the following is an assumption the biologist’s argument requires?
A. Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles.
B. Exposure to artificial light affects the brain differently than exposure to natural light.
C. Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.
D. Early mammals had healthier sleep cycles than most mammals have today.
E. Bright artificial light typically exceeds the intensity of daylight in natural environments.
19 Feb 2026, 14:32
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Official Solution:
Biologist: Early mammals spent most of their time in environments with low light levels, such as forests and burrows. As a result, mammals today are naturally adapted to dim lighting. Hence, regular exposure to bright artificial light is likely to interfere with maintaining proper sleep cycles.
Which of the following is an assumption the biologist’s argument requires?
A. Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles.
B. Exposure to artificial light affects the brain differently than exposure to natural light.
C. Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.
D. Early mammals had healthier sleep cycles than most mammals have today.
E. Bright artificial light typically exceeds the intensity of daylight in natural environments.
The biologist concludes that bright artificial light is likely to interfere with proper sleep cycles. The reasoning is that since early mammals lived mostly in dim environments, modern mammals are naturally adapted to dim lighting. For this conclusion to follow, the argument must assume that the conditions to which mammals are naturally adapted play at least some role in determining whether their sleep cycles function properly.
(A) This choice discusses a correlation between brightly lit environments and irregular sleep cycles. The argument does not rely on such empirical comparisons; it relies on evolutionary adaptation, so this is not required.
(B) The argument does not depend on any distinction between the effects of artificial light and natural light. Thus, this choice is irrelevant.
(C) Correct. If modern mammals’ sleep cycles depend in part on being in environmental conditions to which they are naturally adapted, then being adapted to dim lighting would support the conclusion that bright artificial light interferes with sleep. The argument requires this link.
(D) The argument makes no claim about the sleep cycles of early mammals. Their sleep quality is not relevant to the conclusion.
(E) Whether artificial light exceeds natural daylight in intensity has no bearing on the reasoning. The conclusion does not depend on such a comparison.
Answer: C
Biologist: Early mammals spent most of their time in environments with low light levels, such as forests and burrows. As a result, mammals today are naturally adapted to dim lighting. Hence, regular exposure to bright artificial light is likely to interfere with maintaining proper sleep cycles.
Which of the following is an assumption the biologist’s argument requires?
A. Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles.
B. Exposure to artificial light affects the brain differently than exposure to natural light.
C. Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.
D. Early mammals had healthier sleep cycles than most mammals have today.
E. Bright artificial light typically exceeds the intensity of daylight in natural environments.
The biologist concludes that bright artificial light is likely to interfere with proper sleep cycles. The reasoning is that since early mammals lived mostly in dim environments, modern mammals are naturally adapted to dim lighting. For this conclusion to follow, the argument must assume that the conditions to which mammals are naturally adapted play at least some role in determining whether their sleep cycles function properly.
(A) This choice discusses a correlation between brightly lit environments and irregular sleep cycles. The argument does not rely on such empirical comparisons; it relies on evolutionary adaptation, so this is not required.
(B) The argument does not depend on any distinction between the effects of artificial light and natural light. Thus, this choice is irrelevant.
(C) Correct. If modern mammals’ sleep cycles depend in part on being in environmental conditions to which they are naturally adapted, then being adapted to dim lighting would support the conclusion that bright artificial light interferes with sleep. The argument requires this link.
(D) The argument makes no claim about the sleep cycles of early mammals. Their sleep quality is not relevant to the conclusion.
(E) Whether artificial light exceeds natural daylight in intensity has no bearing on the reasoning. The conclusion does not depend on such a comparison.
Answer: C
