Its all part of the same system. They have no winter because its fucking hot as shit basically year round. It being hot as shit made everything fucking miserable, from dangerous animals to lack of water.

As in, they couldn't afford to put water in the ground for food later because they need to drink now. Nor could they always afford to stay in one place as they had to follow herds for food today rather than later. This isn't 100% the case all the time, but simply having fucking water, and with it fertile land another major lacking in the rest of the continent, is a major reason why Egypt is such an outlier in the continent even before Europe got involved.

Not to mention the lack of natural borders like mountains in Africa specifically meant constant tribal warfare, and the burning and moving it brought. The having of this, and all the forests, likely contributed to South America, despite being similarly uncivilized, being able to develop some stronger development.

They are all retarded, but part of the reason is because their environment selected the most retarded, but hardy and brutish genes to pass on. And the lack of ability to build surplus meant they couldn't develop very well beyond that, because when you are physically lacking you don't really think about higher concepts that can improve.

That's evolution literally at play. And its why you can't just bring a nigger or, worse, a Brazilian into modern society with food and education and create a civilized gentleman.