Question

Which is the most likely reason that lactose tolerance alleles selectively swept through certain human populations?

1) Drinking lots of milk caused a greater mutation rate
2) Lactose intolerance reduced reproduction
3) Lactose tolerance had a large effect on survival
4) It was random which populations experienced the selective sweep
5) None of these reasons explains the selective sweep

Answer 1

Lactose tolerance alleles likely became widespread in certain populations because individuals with lactase persistence had a survival advantage during the development of dairy farming, leading to more successful reproduction and the spread of the genetic trait.

Step-by-step explanation:

The most likely reason that lactose tolerance alleles selectively swept through certain human populations is that lactase persistence provided a considerable survival advantage during the shift from hunting and gathering to agriculture, particularly dairy farming. Lactose tolerance allowed individuals with the genetic trait to digest milk and obtain critical nutrients, which would have been a significant advantage in periods of food scarcity or when other nutrient sources were less available.

This condition of being able to digest lactose allowed individuals within these populations to have access to a consistent food source, and possibly a nutritionally advantageous one that could have enhanced their health and reproductive success. As such, through the process of natural selection, those with lactose tolerance were more likely to survive and reproduce, spreading the lactase persistence alleles throughout the population over generations.