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Difficulty: MediumDistinguishing Main Idea from Supporting Evidence

Read the passage below and answer the question that follows.

For decades, evolutionary anthropologists seeking to explain the marked expansion of neocortical volume in anthropoid primates predominantly favored the social brain hypothesis. This framework posits that the cognitive demands of navigating complex, dynamic social networks—such as managing tactical deception, coalition formation, and dominance hierarchies—served as the primary selective driver for encephalization. Proponents of this view frequently point to strong correlations between relative neocortex size and mean group size across various extant primate species as empirical confirmation that sociality drove cognitive evolution.

However, recent comparative analyses incorporating broader phylogenetic datasets and ecological variables have challenged the primacy of social driving factors. Researchers examining dietary regimes revealed that frugivorous primates possess significantly larger relative brain sizes than folivorous species of comparable body mass, regardless of group size. Processing patchily distributed, ephemeral fruit resources requires sophisticated spatial memory, temporal mapping, and extractive foraging strategies—cognitive demands that operate independently of social group dynamics. Consequently, while social complexity undoubtedly influenced cognitive architecture, it was likely the metabolic availability of high-energy nutrient sources alongside the spatial-foraging demands of frugivory that established the fundamental evolutionary prerequisite and initial selection pressure for expanded primate brain capacity.

Which of the following best expresses the central thesis of the passage?

  1. While social interaction contributed to primate encephalization, dietary complexity and foraging demands constituted the primary driver and metabolic foundation for brain expansion.Answer
  2. B
    Frugivorous primates possess significantly larger relative neocortex sizes than folivorous primates of comparable body mass.
  3. C
    The cognitive demands of managing tactical deception and maintaining dominance hierarchies served as the chief evolutionary catalyst for primate brain evolution.
  4. D
    Social group dynamics played no meaningful role in shaping the cognitive architecture of anthropoid primates.
  5. E
    Relative neocortex size in anthropoid primates is determined exclusively by mean group size rather than by ecological variables.

Answer

The main idea of the passage is that while social complexity played a role in primate brain evolution, dietary factors and spatial foraging demands provided the primary selection pressure and metabolic foundation for encephalization.
The correct answer accurately synthesizes the passage's central thesis. The author begins by summarizing the traditional social brain hypothesis and then uses contrastive structural markers ('However', 'Consequently') to argue that dietary complexity (frugivory) and energy availability were the principal drivers of primate brain expansion, while still acknowledging that social factors played a secondary or complementary role.

Step-by-Step Solution

1
Analyze the structural organization of the passage.
Paragraph 1 outlines the traditional 'social brain hypothesis'. Paragraph 2 introduces a structural pivot ('However') presenting recent research favoring dietary and ecological drivers.
Identifying paragraph functions clarifies how evidence is structured to support the main argument.
2
Distinguish between the supporting evidence and the author's ultimate conclusion.
The comparison between frugivorous and folivorous primates serves as empirical evidence supporting the broader claim that dietary demands and energy availability drove encephalization.
Specific details must not be mistaken for the comprehensive main thesis.
3
Evaluate the option choices against the identified main thesis.
The option highlighting dietary complexity and foraging demands as the primary driver while acknowledging social contributions accurately captures the entire scope of the passage.
The correct main idea option must encapsulate the author's core claim without overstating or focusing narrowly on sub-details.

Key Concept

Distinguishing Main Idea from Supporting Evidence
Estimated Time:2m 0s
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Distinguishing Main Idea from Supporting Evidence