Evolution of water conservation in humans

Area of Science:

• Human evolution
• Comparative physiology
• Water balance

Background:

• Maintaining water balance is crucial for terrestrial animals.
• Human water balance evolution is unclear due to limited comparative data from other hominoids.
• Great apes typically get water from food and rarely drink, unlike humans.

Purpose of the Study:

• Compare water turnover in humans and other apes.
• Investigate factors influencing water balance across species.
• Understand the evolution of human water conservation adaptations.

Main Methods:

• Used isotope-depletion to measure water turnover (L/d) in chimpanzees, bonobos, gorillas, orangutans, and diverse human populations.
• Analyzed relationships between water turnover and total energy expenditure (TEE), physical activity, climate, and fat-free mass.
• Controlled for environmental and physiological factors in comparative analyses.

Main Results:

• Water turnover strongly correlated with TEE, activity, climate, and fat-free mass across all subjects.
• Humans exhibited 30-50% lower water turnover than apes, even with higher sweating capacity.
• Apes in captivity had similar water turnover to wild populations, but ingested more water relative to dry food matter.

Conclusions:

• Humans evolved distinct water conservation adaptations, targeting a lower water/energy intake ratio than apes.
• Water stress from environmental and dietary changes likely drove these evolutionary adaptations in hominins.
• Understanding these differences is key to comprehending human physiological evolution.