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Question #46487
The Question
The 'Expensive Tissue Hypothesis' in human evolution proposes a metabolic trade-off between the size of the digestive tract and the brain. Suppose a hypothetical early hominid population, whose diet consists strictly of complex plant polysaccharides, experiences a permanent environmental shift that eradicates their symbiotic gut methanogens (Archaebacteria). Assuming their diet remains unchanged, which of the following evolutionary consequences is most likely to occur over successive generations?
Options
- A.
An evolutionary increase in cranial capacity, as the metabolic energy previously consumed by the gut microbiota is reallocated to the developing neocortex.
- B.
A gradual regression in cranial capacity, because the decreased production of volatile fatty acids lowers the net caloric harvest required to maintain a large brain.
- C.
Rapid encephalization, as the host genetically upregulates endogenous cellulase production to compensate for the loss of microbial digestion.
- D.
An expansion of the gut volume accompanied by a simultaneous increase in cranial capacity to forage more efficiently for high-calorie foods.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Hominid Cranial Capacity|Methanogens Metabolism
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often misinterpret the symbiotic relationship of gut microbiota, viewing them as metabolic competitors rather than essential facilitators of caloric harvest (via VFAs).
The question requires synthesizing the bioenergetics of microbial fermentation (Microbes in Human Welfare) with the evolutionary trajectory of hominid cranial capacities (Evolution), testing the understanding that brain expansion is strictly dependent on a massive, sustained energy surplus.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Evolution - Class 12 |
| Concept | Hominid Cranial Capacity |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |