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Home/Anthropology/Mains PYQ/2017/Paper I/Human Genetics & Human Biology
UPSC MainsAnthropology Optional Paper I 2017 15 Marks Model Answer Available

Responses and Acclimatization to High Altitude Stresses — 2017 Paper I

Question · 2017 · Paper I · 15 Marks

Discuss the responses and acclimatization to high altitude stresses.

Model Answer

VAID ICS

Approach

  • Demand of Question:Explain the stresses created by high altitude and distinguish immediate responses, acclimatization and longer-term population adaptation.
  • Structuring the Response:Begin with hypobaric hypoxia; discuss respiratory, cardiovascular and haematological acclimatization; then compare Tibetan, Andean and Ethiopian adaptations and note maladaptation.
  • Key Dimensions to Cover:Hypobaric hypoxia; hyperventilation; EPO and haemoglobin; 2,3-BPG; acclimatization; Tibetan EPAS1/EGLN1, Andean high haemoglobin, Ethiopian pattern; chronic mountain sickness.

Model Answer

Introduction High-altitude environments (typically above 2,500 meters) impose severe physiological stresses on the human body. While extreme cold, high UV radiation, and arid winds are significant factors, the primary and most lethal stressor is hypobaric hypoxia (reduced atmospheric pressure leading to a lower partial pressure of oxygen in the blood).

Body

  1. Immediate Responses (Accommodation)When a lowlander first ascends to high altitude, the body triggers immediate compensatory mechanisms to maintain oxygen homeostasis:
  • Hyperventilation: Breathing rate and depth increase instantly to bring more oxygen into the lungs.
  • Tachycardia: Heart rate and cardiac output spike to pump available oxygenated blood faster to vital organs.
  • Side effect: Hyperventilation expels too much CO2, leading to respiratory alkalosis (altered blood pH).
  1. Acclimatization (Short-Term Reversible Changes)Over days and weeks, the body undergoes functional physiological changes:
  • Hematological Changes: The kidneys secrete the hormone Erythropoietin (EPO), which stimulates the bone marrow to produce more red blood cells (RBCs) and hemoglobin, increasing the blood's oxygen-carrying capacity.
  • Cellular Changes: An increase in the enzyme 2,3-BPG lowers hemoglobin's affinity for oxygen, allowing it to release oxygen more easily to oxygen-starved tissues.
  • Capillary density in muscles increases to shorten the diffusion distance for oxygen.
  1. Genetic Adaptation (Long-Term Evolutionary Changes)Populations that have lived at high altitudes for millennia have evolved distinct, genetically encoded adaptations. Interestingly, different populations solved the hypoxia problem differently (Convergent Evolution):
  • Andean Highlanders (South America): Exhibit larger barrel-shaped chests, greater lung volumes, and naturally elevated hemoglobin levels.
  • Tibetan Highlanders (Himalayas): Have mutated EPAS1 and EGLN1 genes (inherited from Denisovans). Unlike Andeans, Tibetans maintain low hemoglobin levels (preventing dangerous blood thickening/viscosity) but compensate with heavily increased blood flow and nitric oxide synthesis to dilate blood vessels.
  • Ethiopian Highlanders: Show neither the high hemoglobin of Andeans nor the specific genetic pathways of Tibetans, possessing a unique, still poorly understood genetic adaptation.
  1. MaladaptationFailure to acclimatize can result in life-threatening conditions like Acute Mountain Sickness (AMS), High Altitude Pulmonary Edema (HAPE), or Chronic Mountain Sickness (CMS), characterized by excessive blood viscosity and right-heart failure.

Conclusion High-altitude biology perfectly illustrates human plasticity and evolutionary resilience. It demonstrates how humans achieve oxygen homeostasis not through a single, uniform 'high-altitude type', but through a complex continuum of immediate physiological responses, reversible acclimatization, and divergent genetic adaptations.

2026 Genetic polymorphism and natural selection. 2026 Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples. 2026 Distinguishing features of nuclear and mitochondrial DNA. 2026 How would you find out that a particular disease/disorder is inherited and, if so, in which manner? Elaborate with suitable examples.

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