Two limbs combined with afro hair (https://en.wikipedia.org/wiki/Afro https://en.wikipedia.org/wiki/Afro) which acted as a sun shade allowed humans to move fast

Two limbs combined with afro hair (https://en.wikipedia.org/wiki/Afro https://en.wikipedia.org/wiki/Afro) which acted as a sun shade allowed humans to move faster and longer at midday in Africa than most of their prey. Lack of sun hitting the body being upright plus sweat from the largely hairless skin made them overheat less than the prey.