The Importance of Population Density

There's no really good reason that humans, unless we're going to totally write human diaspora theory, wouldn't start in one place and move to all those other regions fairly easily. The only continent that didn't have essentially indigenous people who migrated to there and then settled there is Antarctica. Everything else definitely has people living there at some level of population density and technology. Now what that level is depends on a lot of the choices we are going to make right now, but definitely on some level.