system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did early humans migrate out of their homelands to and across much more inhospitable environments?

To my understanding, the first recognizably human beings originated around Ethiopia, in a warm climate which they were well adapted to. At some point, across millions of years, early human migrations spread the species across nearly the entire planet. But why? What possessed them to leave warm and plentiful lands to, say, cross Siberia or the Bering Strait land bridge, where cold temperatures that they were not physically designed to inhabit could cause them to freeze to death? What possessed them to get on primitive rafts and cross oceans to land in Australia or South America?
gpt
It was a very slow process. Some theories state that humans actually followed the same habitat as it moved north following the end of an Ice Age. Also keep in mind that we're talking a really long time scale. It's not like a group just picked up from Africa and walked to Siberia. The groups gradually moved further into the colder regions over thousands of years, with their technology and physiology adapting to give them the ability to survive as they went.