Lecture Notes: The Evolution and Cultural Impact of Lactase Persistence

Introduction

• Humans originally lived as hunter-gatherers.
• Around 10,000 years ago, began domesticating animals, living in settlements, and cultivating crops.
• Cultural changes had profound biological impacts.
• Focus on milk consumption as an example of human co-evolution of culture and biology.

Milk and Lactase Enzyme

• All mammals can digest milk as infants due to the enzyme lactase.
• Lactase breaks down lactose into glucose and galactose.
• Mammals typically stop producing lactase after weaning, becoming lactose intolerant.
• Many adult mammals, including most humans, cannot digest lactose without symptoms like cramps and diarrhea.

Lactase Persistence

• Approximately one-third of adults worldwide are lactase persistent, meaning they can digest milk.
• The trait is due to the continued production of the lactase enzyme.

Genetic Investigation

• Researchers explored DNA differences between lactase persistent and intolerant individuals.
  • No initial differences found in the lactase gene itself.
  • Found a mutation (T instead of C) in a non-coding region among Europeans.
  • Different mutation found in the Maasai of Africa, indicating independent evolutionary events.

Role of Pastoralism

• Both Maasai and early Europeans were pastoralists.
• Cattle were central to their culture and economy.
• Evolution of lactase persistence likely linked to milk consumption.

Archaeological Evidence

• Richard Evershed studied ancient pottery for milk fat residues, confirming ancient dairy use.
• Milk use dates back 7,000 to 9,000 years ago.
• Correlation between the spread of lactase persistence mutations and early dairy use.

Genetic Adaptation

• Lactase persistence likely provided a selective advantage.
• In famine, ability to digest milk increased survival chances.
• Estimated selective advantage of 5-10%.
• Gene-culture coevolution played a crucial role in human evolution.

Conclusion

• The study of lactase persistence illustrates gene-culture coevolution.
• Understanding human evolution requires considering both biological and cultural factors.