Vsauce Lecture: Human Size and Its Limits

Historical Increase in Average Height

• People today are ~10cm (4 inches) taller on average than 150 years ago
• Better nutrition and medical care contribute to this increase
• Genetic blueprints determine maximum potential height in optimal environments
• Maximum human height rarely exceeds 7 feet 6 inches

Cases of Extreme Height

• Endocrine disorders: Tumors near the pituitary gland can lead to abnormal growth
• Igor Vovkovinskiy: 7'8", tallest man in America
• Sultan Kösen: 8'3", tallest living person and record for largest hands and feet
• Robert Wadlow: 8'11", tallest person ever recorded
• Andre the Giant: 7'4"

Biological Limits to Height

• Average human height today is near the genetic limit
• Genetic manipulation might add up to 15cm to average height
• Increased height would require different body proportions due to the square-cube law
  • Square-cube law: Volume increases faster than surface area as size increases
  • Larger humans would need proportionally thicker bones or stronger materials
  • Larger size also creates issues for the cardiovascular system

Examples of Large Animals

• Giraffatitan: Largest land animal known, weighed 20,000-30,000 kg
• Bruhathkayosaurus: Potentially larger, estimated at 140,000 kg; controversial due to limited evidence
• Blue Whale: Heaviest known animal, up to 177,000 kg; buoyancy aids in water

Martian Growth Potential

• Humans could grow taller on Mars due to lower gravity (1/3 of Earth's)
• Trade-off: Weaker bones and muscles, making Earth visits difficult

Sensory Perception and Size

• Angular Size: Determines how large an object appears from a distance
  • Thumb arm-length: ~1 degree
  • Moon: ~0.5 degrees
  • Minimum visible: ~1 arc minute (~1/60th of a degree)
  • Sunspots: ~20 arc seconds (1/180th of a degree)

Maximum Visible Distances

• Naked eye visibility: Up to 10-15 km under ideal conditions
• Horizon limit: ~5 km on Earth's surface due to curvature
• Smell: Animals (e.g., Bloodhound) can detect scents from 30 km away

Emission and Detection Limits

• Human body emits infrared and visible light, tied to circadian rhythms
• Light emission can theoretically continue indefinitely into space
• Distance to detect single photons: ~168,000 km

Conclusion

• Human physical size is limited by geometry, biology, and gravity
• Sensory dimensions (sound, smell, sight) are bounded by Earth's limits
• Light emission from the human body potentially leads to an