Answer:
The increase of lighter skin color alleles in northern populations is most likely favored by: a. Directional selection (positive selection)
Step-by-step explanation:
Directional selection occurs when a particular trait is favored, leading to an increase in the frequency of alleles associated with that trait over time. In the case of lighter skin color in northern populations, this adaptation is often associated with the need to absorb more sunlight to synthesize sufficient vitamin D in regions with lower UV radiation. Lighter skin is better at absorbing sunlight, and in regions with reduced UV radiation, individuals with lighter skin may have a survival advantage because they can more efficiently produce vitamin D, which is essential for overall health. Stabilizing selection, on the other hand, would favor the maintenance of an existing trait (in this case, an intermediate skin color), while genetic drift is a random process that is less likely to result in the consistent increase of specific alleles for a particular trait in a population.