Domestication also explains, why development has been slower in Africa. They had nothing to domesticate.
many points are debated here, there are also some links to start https://www.quora.com/Farming-Why-didnt-the-Native-Americans...
disclaimer: I know nothing of the subject and my initial hunch was pure conjecture.
I'd be pretty interested in seeing a domesticatability comparison of the guanaco (wild predecessor of the domesticated llama still in existence today) vs. the zebra.
[0] https://en.wikipedia.org/wiki/Domestication_of_animals#Behav...