Human Evolution and Lactase Persistence

Introduction

• Humans evolved around 200,000 years ago as hunter-gatherers.
• About 10,000 years ago, humans started domesticating animals and farming.
• These changes had significant biological impacts, including the ability to digest milk in adulthood.

Lactase Enzyme and Milk Digestion

• Infant Mammals: All can digest milk due to the enzyme lactase.
• Lactase Function: Breaks down lactose (a sugar in milk) into glucose and galactose for energy.
• Lactose Intolerance: Most mammals, including humans at some point, stop producing lactase as they grow, making them lactose intolerant.

Lactase Persistence in Humans

• Unique to Humans: Some adults can digest lactose; around a third of all adults globally.
• Lactase Persistence: Ability to produce lactase throughout life.
• Geographical Variations: More common in Europe; less common elsewhere.

Genetic Basis of Lactase Persistence

• Discovery of Mutations:
  • In Europeans: A T instead of a C at a non-coding region correlated with lactase persistence.
  • In Africans, specifically the Maasai: Found a different mutation leading to the same trait.
  • These mutations arose independently in different populations.

Historical and Cultural Context

• Pastoralists Influence: Both the Maasai and early Europeans domesticated animals and consumed milk.
• Archaeological Evidence: Milk use found in pottery from ancient settlements in Europe and Africa over 9,000 years ago.

Gene-Culture Coevolution

• Mutations and Selection Pressure:
  • Mutations for lactase persistence provided a selective advantage in dairy-consuming cultures.
  • Estimated selective advantage could lead to a 5-10% increase in survival in dairy-dependent populations.

Hypotheses for Selective Advantage

• Nutritional Benefits: Milk is rich in protein and fat, providing high-quality nutrition.
• Safety Factor: Milk is relatively uncontaminated compared to other food sources.
• Agricultural Context: Failure of crops could make dairy a critical food source.

Conclusion

• Gene-Culture Coevolution: The evolution of lactase persistence is a prime example of coevolution between human genes and culture.
• Broader Implications: Understanding human evolution requires considering cultural evolution alongside biological changes.