What is the Anthropological explanation behind why certain nationalities have longer peni than others?

well, i know that the spines of the Stegosaurus were to increase its surface area, allowing a form of "air conditioning" to take place. of course, in africa it is very hot, yet in asia, the asian people are descendants of nomadic peoples that migrated north from africa into russia and evolved there for a few thousand years where it was very snowy and then migrated sort of southeast to siberia, where it is also cold and snowy (my theory for their asian eyes, they are merely vestigial adaptations to prevent snow blindness). but look at the inuit people, short arms and legs and a short nose to prevent against frostbite and to keep better homeostasis, and a large would not come in handy in sub zero temperatures. yet in africa, the heat allows the evolution of the to grow to any extent.