Black people have bigger dicks, ears , lips, and noses because these areas have a lot of blood vessels close to the surface of the skin. Increased surface area helps expel heat to regulate their internal temp under the hot equatorial sun.
Interestingly enough, Alice looked up the global average dick sizes for various regions, and the areas of Africa where dick size is above average correlates with area covered in jungles. Humidity in these areas would make sweating a less effective method of temperature self-regulation, so locals evolved different methods of temperature regulation.
Not dying of heat-stroke gives an individual more time to breed and pass on their big-dick genes.