Our behinds are larger to store fat in a place where we can stay cool rather than on legs or arms. We tend to be taller because taller, lean bodies dissipate heat better. Straight hair warms the head and neck. There is a biological reason why our lips are larger. I'd love to know the answer.
Black people seem to have the largest features of all the races because of adaptation.
If you are willing to know the true answer, you must study. Black people tend to have the larger features because when we were in Africa, we had to adapt to the hot climates. That's why our skin is deep in melanin - to protect us against the sun's rays. Melanin is the dark pigment that gives us our color. We have larger noses to be able to breathe in the humid air of Africa.