Muscle and bone structure through selective survival. Niggers are great at sprinting. It's the primitive hunters best traits. If you have a spear you need to get within arms length to get a thrust to go through hide. They also where not using sharpened stone tips as often as just cutting the stick to a sharp point. Would take a handful of men to take down a boar. Europeans had advanced faster, used copper, bronze, iron, and later steel. Europeans advanced technologically while Africans still advanced physically.
The less tools you use for ease and the more you use your hands and brute strength, the stronger you will be.
Is there any proof that Blacks are more athletic and Asians are less athletic?
Adam Robinson
Ethan Lopez
To further this line of reasoning, if you subscribe to the thought that white brains developed to survive winters, then you also have the necessity to build structures that survive winters. Body bulk would benefit both for building more durable structures out of wood and stone as well as being a source of stored calories in a long winter, so you get the white intelligent strong man from those environmental pressures.