Guns, Germs and Steel (Civilizations Rise and Fall, #1)

by Jared Diamond

and from the Philippines east to Polynesia (at 3.2 miles per year). At the opposite extreme was its slow spread along north-south axes: at less than 0.5 miles per year, from Mexico northward to the U.S. Southwest;

This isn't much slower than the Fertile Crescent to Indus Valley rate.