Oily Birds: Biology forum question

Five different mutations are known to be associated with keeping lactase production turned on into adulthood—a trait called lactase persistence. All five mutations(shown in the figure below) occur in a regulatory element, known as a genetic “switch,” for the lactase gene on chromosome 2. The lactase switch is in a segment of DNA in a neighboring gene called MCM6, and all the mutations are within two of the introns of that gene. (In the figure below, the introns are light blue and the exons dark blue.)

Genetic analysis suggests that the mutations associated with lactase persistence arose less than 10,000 years ago. They increased in frequency in populations that were pastoralist—which means they kept and used domesticated animals. A practice like pastoralism is called cultural because it is taught and learned and it is not an instinct dependent on the transmission of genetic variations (see last discussion point). In pastoralist populations, individuals with the lactase persistence mutations were more likely to survive, reproduce, and pass on their alleles than people without the mutations, especially in times of famine. What’s more, individuals only need one copy of the mutated switch to be lactase persistent; thus, the traitis inherited in a dominant pattern. Over just a few dozen generations,the frequency of the lactase-persistence allele could have increased rapidly under intense positive selection. The increase in the number of individuals in these populations that were lactase persistent meant that more and more people would depend on milk from their livestock herds, especially cows, further promoting the culture of pastoralism.