There's still a lot we don't know about the first human colonization of the Americas, particularly the exact timing, but we do know that it took tens of thousands of years for humans to make it from Alaska to Chile.
When modern humans left Africa roughly 100 thousand years ago, it was only the last of several waves of hominoid migration that had previously included the likes of Neanderthals and Homo Erectus. Now a tooth in Germany reveals the original hominoid migration.
We can trace our evolutionary heritage back millions of years, but it's surprisingly tricky to say with certainty which hominid species came directly before us. Now it looks like one of our evolutionary cousins is actually our parent species.