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Home/Anthropology/Mains PYQ/2021/Paper I/Human Evolution & Primatology
UPSC MainsAnthropology Optional Paper I 2021 10 Marks Model Answer Available

The Losses and Gains of Erect Posture — 2021 Paper I

Question · 2021 · Paper I · 10 Marks

The losses and gains of erect posture

Model Answer

VAID ICS

Approach

  • Demand of Question: Explain the evolutionary advantages and anatomical costs associated with habitual erect posture and bipedalism.
  • Structuring the Response: Briefly explain erect posture, then discuss major gains and losses with evolutionary significance.
  • Key Dimensions to Cover: Freeing of hands, efficient locomotion, thermoregulation, vision, spinal stress, foot disorders and childbirth.

Model Answer

Introduction

Erect posture and habitual bipedalism are defining features of hominin evolution, involving major modifications of the vertebral column, pelvis, lower limbs, foot and position of the foramen magnum.

Gains of Erect Posture

  • Freeing of hands: The forelimbs became available for carrying food and infants, tool-making and manipulation, strengthening the hand–culture relationship.
  • Efficient locomotion: Rodman and McHenry (1980) argued that habitual human bipedal walking is energetically more efficient than chimpanzee locomotion and may have favoured movement across wider ranges.
  • Better visual surveillance: Increased height improved the ability to observe resources, predators and conspecifics in open environments.
  • Thermoregulatory advantage: P.E. Wheeler (1991) proposed that erect posture reduces direct solar exposure and increases convective and evaporative cooling in open tropical environments.
  • Greater ranging ability: Long legs and efficient bipedalism eventually enabled hominins such as Homo erectus to walk long distances.

Erect posture → Free hands + Efficient gait + Better surveillance + Thermoregulation

Losses or Costs

  • Spinal problems: Upright weight transmission places greater stress on the vertebral column, contributing to lower-back pain, slipped discs and degenerative changes.
  • Joint and foot stress: Body weight concentrated on two limbs increases susceptibility to hip and knee arthritis and collapsed foot arches.
  • Difficult childbirth: Pelvic adaptations associated with bipedalism, combined with later encephalisation, contributed to a relatively tight and complex human birth canal. S.L. Washburn (1960) termed this evolutionary trade-off the “obstetrical dilemma,” though its precise explanation remains debated.
  • Reduced arboreal efficiency: Long lower limbs, shortened toes and a rigid arched foot improved terrestrial walking but reduced the grasping and climbing capacities seen in apes.

Conclusion

Erect posture was therefore a major adaptive breakthrough in hominin evolution, facilitating locomotion, manipulation and cultural development. However, these gains came with significant biomechanical and reproductive costs, making bipedalism a classic example of evolutionary trade-offs.

2026 Human evolution is a product of both biological and cultural factors. Elaborate. 2026 Discuss the phylogenetic status, characteristic features, geographical distribution and lifeways of Paranthropus. 2026 What are Strepsirhini Primates? Describe their geographical distribution and mention the characteristics that distinguish them from Haplorhini Primates. 2026 Seed Eaters Model of hominid differentiation.

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UPSC Anthropology Optional 2021 — Paper I

28 questions

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5(e) Modes of Subsistence

10 Marks150 words
Syllabus: Paper I > 3. Economic Organization > Modes of subsistence
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5(b) The losses and gains of erect posture

10 Marks150 words
Syllabus: Paper I > 1.5 Characteristics of Primates > Skeletal changes due to erect posture
2021Paper IHuman Evolution & PrimatologyModel answer available

1(e) Thermoluminescence (TL) dating

10 Marks150 words
Syllabus: Paper I > 1.8(a) Chronology: relative and absolute dating methods
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