Question

Many humans are lactose intolerant after a certain age and are no longer able to break down the lactose in fresh milk. Approximately 20,000 years ago, a mutation occurred in the lactase gene (responsible for breaking down lactose sugar), giving some people the ability to digest lactose throughout their lives. Eight thousand years ago, there was a famine when crops failed, and diets had to change.

Which type of mutation does this represent?


It is a neutral mutation because there are many food choices.


It is a beneficial mutation as there are now food options available.


It is a harmful mutation because people do not always have access to milk.


It is a beneficial or a neutral mutation depending on the diet of the population.

Answer 1

It is a beneficial or a neutral mutation depending on the diet of the population.

Explanation: lactase persistence is advantageous (positive selection) where dairy is an important food source (e.g., during famines or in pastoralist societies), but in populations that don’t consume milk it has little or no effect and is effectively neutral.