Anthropologists say they believe ancient peoples in Europe and Asia moved primarily along east-west routes in similar climates, allowing technological advances to spread quickly, but North and South America -- with their long, north-south orientation and great variability in climate -- slowed that movement.
Researchers at Brown University and Stanford University said genetic studies suggest after humans arrived in the Americas 20,000 to 40,000 years ago there was less interaction between populations than in Eurasia.
"If a lack of gene flow between populations is an indication of little cultural interaction," the researchers write in the American Journal of Physical Anthropology, "then a lower latitudinal rate of gene flow suggested for North American populations may partly explain the relatively slower diffusion of crops and technologies through the Americas when compared with the corresponding diffusion in Eurasia."
"It's harder to traverse those distances based on climate than it was in Eurasia," Brown researcher Sohini Ramachandran said. "We find greater genetic differences (in the Americas' populations) because of the difficulty in migration and the increased challenge of reuniting with neighboring populations."