QUESTION $15$

Hypothesis $2$: Since folate is essential for reproductive success, the need to sustain folate levels led to human skin color variation.

Hypothesis $3$: Since vitamin D is essential for reproductive success, the need to sustain vitamin D levels led to human skin color variation.

The two hypotheses above are both rejected as explanations of how the wide variety of human skin colors have evolved because they each only answer part of the puzzle. Hypothesis $2$ cannot explain human skin color variation because it only covers why $,$ skin evolved and not other skin tones. Hypothesis $3$ cannot explain human skin color variation because it only covers

$$ skin evolved and not other skin tones.