Answer: food is a least likely reason
Explanation: The equator is an imaginary line that divides the earth between two halves (north and south).
The polar settlers or those that are farther away from the equator eats food that contains vitamin D. They get the vitamin from food as an alternate source.
The tropical settlers feed mostly on foods that are high in carbohydrate.
However, melanin is a pigment that is usually brown, it is a natural sunscreen that sheilds tropical settlers from the many harmful effects of ultraviolet (UV) rays.