Explain how a mutation has caused the Lactase Persistence gene in some people and not in others.

It is a case of human niche construction

Explanation:

Lactase is an enzyme of mammals which is required to digest lactose. In humans (like in other mammals), lactase activity decreases during mid-childhood; although there are individuals which are still capable of producing this enzyme even during adult life, a trait known as 'lactase persistence'.  Different mutations in the coding region of the lactase gene have been associated with lactase persistence in European, African and Asian populations. On the other hand, the niche construction theory states that the organisms, through their activities and choices, actively modify their own local environment by introducing novel selection pressures. Some examples of niche construction include, among others, alternation of nutrient cycling by plants or lactase persistence in humans. Lactase persistence can be defined as a case of niche construction because this trait was not only genetically inherited but also culturally transmitted through local environments shaped by ancestral populations, i.e., generated by niche construction or ecological inheritance.

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