Lecture on Human Evolution and Lactase Persistence

Introduction

• Human beings initially lived as hunter-gatherers.
• Around 10,000 years ago, began domesticating animals, forming settlements, and cultivating crops.
• These cultural changes profoundly impacted human biology.

The Case of Milk

• Milk is digestible by almost all infants.
• Adults' ability to digest milk is a case of co-evolution of culture and biology.

Lactose Digestion in Mammals

• All infant mammals produce lactase, an enzyme to digest lactose in milk.
• Lactase breaks lactose into glucose and galactose for energy.
• Most mammals lose the ability to produce lactase after infancy, leading to lactose intolerance.

Human Lactase Persistence

• Only one mammal, humans, has adults who can digest lactose - termed lactase persistence.
• 1/3 of adults worldwide are lactase persistent.

Genetic Basis of Lactase Persistence

• Genetic testing didn't initially show differences in the lactase gene itself between persistent and non-persistent groups.
• Persistence likely due to gene regulation from other DNA segments.

Research Findings

• Discovery of a mutation in non-coding DNA in European lactase persistence.
• Different mutations discovered in African populations (e.g., the Maasai).
• Lactase persistence mutation arose independently in different populations.

Cultural Influence

• Lactase persistence linked to cultural practices of dairying.
• Evidence of early milk use found in ancient pots from Europe and Africa.

Archaeological Evidence

• Milk use dated back 7,000-9,000 years in various regions.
• Genetic mutation spread aligns with archaeological evidence of dairying.

Evolutionary Advantage

• Mutations offer no advantage without dairying.
• Lactase persistence mutation became advantageous with the advent of dairying.
• Provided a strong selective advantage in regions reliant on dairy, especially during times of crop failure.

Gene-Culture Coevolution

• Lactase persistence is an example of gene-culture coevolution.
• Understanding human evolution requires examining both genetic and cultural evolution.