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12 Days of Christmas GMAT Competition 2025 - Day 2: Biologist: Early

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Premise: Early mammals lived in low light and mammals are adapted to low lighting.
Conclusion: Regular exposure to bright light impacts sleep cycles

So sleep conditions today are influenced by conditions mammals are adapted to.

C Made the most sense in this case for me.

Bunuel

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.

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Bunuel

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Conclusion is the last line of the passage. The author assumes that whatever adaption the mammals had earlier is still applicable

A: Incorrect : This is not related and not an assumption of the argument
B: Incorrect : What causes the sleep pattern changes is not of contention and can be eliminated.
C: Correct: If the sleep pattern of the modern mammals don't depend on the adaptation the conclusions falls.
D: Incorrect : Irrelevant. We can eliminate D.
E: Incorrect : Not related to the conclusion of the argument.

Option C

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The correct answer C. because option c state that other factor are contributing to irregular sleep cycle

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Answer is C as modern mammals got adapted by the natural phenomena. Thus, Exposure to artificial light interfere with sleep cycle on which the assumption is based.

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Premise: Early Mammals lived mostly in low light environment ---> They became adapted to low lightings.
Conclusion : Exposure to bright artificial light is likely to interfere with sleep cycles.
Missing link : Sleep cycles are somehow related to the kind of environmental conditions with which mammals are adapted.

A. Strengthening the conclusion but not required assumption or missing link.
B. Not relevant
C. Correct. Connecting the premise and conclusion.
D. Not relevant
E. Not required.

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(A) Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles. Wrong. Strengthens, but need not be true.
(B) Exposure to artificial light affects the brain differently than exposure to natural light. Wrong. Irrelevant comparison.
(C) Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted. Correct. If sleep cycle is not related in anyway, then adaptability to dim light cannot conclude about bright light.
(D) Early mammals had healthier sleep cycles than most mammals have today. Wrong. Irrelevant comparison.
(E) Bright artificial light typically exceeds the intensity of daylight in natural environments. Wrong. Irrelevant comparison.

Ans C

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Bunuel

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A) this is not relevant to the arguement, there can be invariably another reaon to have irregular sleep cycle
B) not very clear, how differnt it is, and how it relates to interefing with sleep cycle
C) negating this statement, would weaken the support for arguement -> this can be right
D)comparison is not apt, not relevant to the arguement atleast
E)the statement would also work if it does not exceeds ( let say matches) the intensity.

Hence answer is C

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Main Conclusion: Regular exposure to bright artificial light is likely to interfere with maintaining proper sleep cycles

A. The argument is trying to link adaptations from a dimly lit environment and the consequence of such mammals that are exposd to bright lights. Not mammals which spend most of their time in brightly lit environment.

B. This goes in the opposite direction of what we are looking for. If artificial light affects it differently than natural light, we cannot make the conclusion that artificial light will cause disturbed sleep cycles.

C. This is the assumption we are looking for. The connection between the facts to the main conclusion is that today's mammals partly depend on the environment in which the mammals adapted. Without this we cannot connect the fact to the main conclusion, hence, making this necessary.

D. The comparison of early mammals and present day mammals is not what the argument is talking about.

E. The negation of this answer choice does not break the argument.

Bunuel

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A. This choice kinda augments the conclusion and is not therefore an assumption
B. The argument has nothing to do with type of light thus out of scope
C. Correct; As evidenced by negation without this assumption the conclusion breaks hence the right choice
D. This comparison is irrelevant because it is not about which mammals slept better
E. The intensity does not matter hence out of scope
Ans C

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The question begins with the biologists view, that Early mammals have spent a greater amount of time in environments, where the light levels are low. To make us understand what are low level light environments, examples of forests and burrows are given as evidences.

We should not forget that mammals include human beings too, and some other species too.

Further explaining, the biologist mentions AS A RESULT - evolution has led the mammals of today to get adapted to dim lighting.
So, a comparison between early mammals and mammals of today is made.

Moreover, the today mammals are NATURALLY capable of adapting to dim light because, early mammals spent a greater amount of time in low light level environments.

The biologists concludes, Exposure to artificial bright lights will interfere in regular sleep cycles. There are words : ARTIFICIAL and BRIGHT LIGHT which are 180 degree variations of NATURAL , DIM or Low Light levels. This bright light has impacted the sleep cycles.

We need to find the assumption :

A) Mammals that spend most of their time in brightly lit environments tend to have a more irregular sleep cycles.

The question mentions mammals being exposed to artificial bright light have irregular sleep cycle. But, the option mentions bright lit environments can be either natural or artificial. Moreover, more irregular sleep cycles, speaks about the frequency of irregularities in sleep cycle. But, the question mentioned there is a likelihood that the sleep cycles can be irregular. Hence, Wrong.

B) Exposure to artificial light affects the brain differently than exposure to natural light.

This option goes beyond the question, thinking out of box as well as out of context bringing brain into picture. Hence, Wrong.

C) Modern mammals sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.

This option is the correct answer. As mammals sleep cycle is impacted at least to some extent on environmental conditions like lights, to which the mammal is naturally adapted. The biologist assumes that natural environment plays a crucial role in impacting sleep cycles.

Let’s apply NEGATION TEST: modern mammals sleep cycle is no where related to the environment conditions to which the mammal is naturally adapted. If that’s the case, then irregular sleep cycles don’t occur. And the conclusion falls apart.

D) Early mammals have healthier sleep cycles than most mammals have today.

The option speaks about healthier sleep cycle, so there can be weak or sick sleep cycles. This is completely out of scope. Wrong.

E) Bright light typically exceed the intensity of daylight in natural environments.

Bright light can be natural or artificial. Sun is a natural bright light, while the electric lights which we use are artificial. Even amongst these two, the difference of intensity prevails. Nothing is of higher intensity or brighter than sun. This option is completely out of scope. Wrong.

Option C

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Arguement core is since mammals are adapted to dim lighting, bright artificial light will interfere with the sleep schedule.

A) we are concerned about the bright artificial light & not all brightly lit environments. Incorrect
B) difference is between bright artificial & natural dim light and not between artificial & natural light. Incorrect
E) Out of context
D) We are concerned about the impact of different light settings on the sleep, irrelevant
C) Negating C, modern mammals sleep cycles doesn't depend in part on environmental conditions to those they are naturally adapted. which means their sleep doesnt depend on dim natural light to which they are adapted. the conclusion falls through as we cant say then if bright artificial light will interfere or not with the sleep schedule. Ans C

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Main Point: Bright artificial light is likely to affect sleep cycles.

Basis:
1. Early mammals spent most of their time in low light environments.
2. Therefore, they are naturally adapted to dim lighting.

Logic: Since the mammals are adapted to dim lighting, they are unlikely to prefer bright light, which is turn could interfere with their sleep cycles.

Gaps:
1. How can we conclude an effect on sleep cycles?
2. It they are adapted to dim lighting, does that necessarily mean that they are unlikely to prefer bright lights?

(A) Out of Scope. It provides an evidence to the conclusion, which could have strengthen the argument. This is not an assumption.

(B), (D), (E) Irrelevant to the argument.

(C) This is correct, as it directly addresses the first gap in the reasoning.

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ANS C:
If sleep cycle did not depend on natural adaptation, bright artificial light wouldn't necessarily interfere

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lets analyse, biologist claims

1) premise 1 - mammals are built for dim light
2) premise 2 - modern mammals still prefer dim light
3) conclusion - bright lights mess up sleep

The missing link or assumption:

The biologist is arguing that because mammals are adapted to dim light, exposing them to a non adapted environment will cause a problem (sleep interference). To make this jump , the biologist must assume that the adaption still matters to the sleep cycle today.

lets look at the options:

option A : This basically a restatement of the conclusion, not a missing link required to support it

option B : This is too specific, whether its artificial or bright natural light, the argument is about brightness interfering with the adaptation.

option C : This statement is the glue. It connects the two facts i.e., adaption (low light ) --> sleep cycles depend on it --> changing it(bright light) ---> causes interference

option D : The argument is about interference now, not historical health comparisons

option E : This focuses on intensity comparison which isn't necessary. The core issue is that bright light interferes with adaptation to dim light.

Therefor the correct answer is option C

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16 Dec 2025, 14:52

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conclusion- regular bright light exposure likely to interfere with maintaining proper sleep cycless
reason- mammals spent most of time in low light levels.
today they are naturally adapted to dim lighting.

from naturally adaption of dim light to interfere with maintaining proper sleep cycle.
big jump in reasoning.
B,D,E are completely out of scope,
C clearly talks about hidden link. author is thinking that natural adaption to light is related to maintaining proper sleep cylce.
so if thats the case C is the assumption

Bunuel

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So I choose the ans C, The logic is straightforward. The comparison an conclusions drawn are based of exposure to dim and bright light in natural environments. The statement c on negation breaks this notion this making me inclined to this option

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Bunuel

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The statement talks about spending time in low light levels , and how bright artifical light is likely to interfere with sleep cycles. there is a clear gap in between the argument and premise ..we need to bridge the gap between sleep cycles and lighting(or enviornment conditions). hence (c) is the right answer.

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This is assumption question type,
Spend time in low lights (dim lights)->adapted to low light for mammals.
Regular bright artificial light(AI) leads to inter with proper sleep.
we need to look for answer choice that connects adaption of light and ai affect on sleep.
1)
We do knot to which extend the relationship is between the amount of AI and sleep interference, what if there is like a saturation curve.we don't know so out
2)
okay exposure to affects differently can be true but there can be more condition that just that so we can eliminate that
3)
depend in parts can be true but is the only condition , when we negate the statement
depend in most part conclusion still holds. so out
4)
early and new are not subject to comparison , there could be other facts contributing to sleep other than just ai
5)
Poe we got e now lets confirm it
bright ai exceeds the natural light loooks like good connection between ai intensity and natural i like it now lets negate it
ai and nautural light are same ; this breaks the conclusion as if they were same it wouldn't interfer.
therefore E is the final answer

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Bunuel

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Conclusion: Bright artificial light interferes with maintaining proper sleep cycles.
Reason: Mammals evolved in a dim environment and adapted to dim light.
Assumptions: Those ancient adaptations still matter for sleep cycles.

A) Correlation, not required.
B) Natural vs. artificial is not our concern. Out of scope.
C) EXACTLY. It sums up our entire assumption.
D) We don't know. Out of scope.
E) Intensity comparison. Again out of scope.

Hence, OPTION C.

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16 Dec 2025, 19:28

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Bunuel

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Premises:
Early mammals spent most of their time in environments with low light levels
Now mammals adapted to dim lighting

Conclusion:
regular exposure to bright artificial light is likely to interfere with maintaining proper sleep cycles.

Here we jump from spending most time in low light, dim light adaptation to interference in sleep cycle due to bright artificial light exposure.
There must be a link between these, and most probably an option describing that link and which must be true is the answer.

(A) Mammals that spend most of their time in brightly lit environments tend to have more irregular sleep cycles.
This would support the conclusion but isn't necessary for the argument's logic to hold.

(B) Exposure to artificial light affects the brain differently than exposure to natural light.
The argument focuses on brightness levels, not light source type, so this distinction of artificial vs natural light isn't required.

(C) Modern mammals’ sleep cycles depend at least in part on environmental conditions to which mammals are naturally adapted.
If sleep cycles DON'T depend on environmental conditions mammals adapted to, then the fact that mammals adapted to dim lighting wouldn't matter for sleep cycles. This assumption is essential for the argument to work .

(D) Early mammals had healthier sleep cycles than most mammals have today.
The argument makes no claims about relative health across time periods.

(E) Bright artificial light typically exceeds the intensity of daylight in natural environments.
The argument contrasts bright artificial light with the dim environments mammals adapted to, not with natural daylight.

Correct Answer C