Early populations of humans leaving Africa had dark colored skin. As these popul

Question

Early populations of humans leaving Africa had dark colored skin. As these populations migrated into northern latitudes, they encountered environments with reduced sunlight as compared to environments at the equator. Humans need exposure to sunlight in order to synthesize vitamin D. Without vitamin D, humans develop soft, bendable bones – known as Rickets in children and osteomalacia in adults. People with dark skin produce more melanin in their skin than people with light skin, and this increased melanin acts as a barrier to sunlight. Thus, people with the darkest skin colors were not able to synthesize vitamin D as effectively as the people with lighter skin colors. Therefore, in northern environments people with dark skin had a lower fitness, survival rate, and reproductive rate than people with light skin.

Which of the following evolutionary forces is most likely involved in this scenario?

A. Mutation

B. Selection

C. Gene Flow

D. Genetic Drift

E. No evolutionary forces are involved

A. Mutation

B. Selection

C. Gene Flow

D. Genetic Drift

E. No evolutionary forces are involved

Explanation / Answer

Option B is correct. In this scenario the people with light skin has been naturally selected for better survival and reproduction because light skin can absorb more light for the production of vitamin D even in reduced sunlight condition like in northern latitude. While the people with dark colour will not absorb more sunlight due to excess melanine (act as barrier for sunlight) in their skin. Hence due to reduced sunlight in northern latitude the people with black skin has not been naturally selected. Thus in this scenario the involved evolutionary force is natural selection.

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