Answer:
For a start, humanity was all over the planet before civilization started. The earliest civilizations began around 5500 years ago, but there’d already been humans all over every continent except Antarctica from about 10,000 years ago, when expanding populations in the Americas reached Tierra del Fuego.
Moreover, there were at least six “cradles of civilization.” Complex urban society was independently developed in Mesopotamia, Peru, Egypt, India, China, and Mexico. So it’s not really the cradle of civilization.
Anyway, humanity didn’t really leave them. Some people did, of course. One thing civilizations do sometimes is form armies and go conquer their neighbors. Other times they send out merchants to do business in foreign lands, and some of them settle there. Mostly, though, when it comes to early civilization, what spread out wasn’t people, but rather ideas. Useful and powerful concepts of social complexity were adopted by neighboring peoples as they saw fit, leading to the rise of new and similar but not identical civilizations around the core of earlier ones.
So, then, humanity did not leave the cradles of civilization. Humanity was already all over the planet long before that happened. What emerged from those places was political control and cultural influence.
Step-by-step explanation:
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