4.) Deeper, looser scrotums are needed to radiate the tropical African heat.
I have wondered about this many times. Black men and Muslim men seem to have the lowest hanging and biggest balls. I think it is due to their original environment of the Sahara desert and Middle Eastern desert. The testicles need to be able to get cool. And the descended ball sack allowed more room for ball growth.
While the White men from cold and rainy climates seem to have tighter scrotums to keep their balls warm. Also their balls are smaller due to the tight ball sack.
As a metaphor, think of how aquarium fish only grow as big as the tank they are keep within.