A Theory on the Evolution of Human Life

If you travel to any part of the world: Europe, Asia, North America, Australia, you name it, you are bound to find humans in the forested areas of those landmasses. When Christopher Columbus arrived in South America, he found natives there. These natives had no technology. Their most advanced technology was a bow and a arrow and a canoe that can only be used to cross rivers. They had no sailing ships or aircrafts. So how did the natives arrive on these landmasses? Where did they come from.