Spread of a Lactase-Persistence Allele

This activity guides the analysis of a published scientific figure from a study that investigated how human populations might adapt to milk consumption, both genetically and culturally. 

As babies, humans produce an enzyme called lactase to break down lactose, the main sugar in milk. Though most people stop producing lactase as they grow older, some have a trait called lactase persistence that allows them to keep producing lactase throughout their lives. One hypothesis suggests that lactase persistence was strongly selected for in populations that traditionally raised animals for milk. 

To investigate this hypothesis, scientists traced the spread of a common lactase-persistence allele through Asia and Europe over the last 10,000 years. Using both ancient and present-day samples, and both genotype and phenotype data, they estimated how common the allele was among people in different regions over time. In the figure, dots indicate the sampled individuals and populations, and the pink/red shading indicates the estimated allele frequency based on the samples.

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