" All this means is that we made assumptions about patterns of migration that were much more linear and spread like ripples, rather than the picture that has emerged in the last couple of years, which says that we moved in all directions all the time, and laid our hats and flowed our genes in a matted crisscross, instead of a nice clean radiation. Oceans and mountains are good barriers to gene flow, but on big open continents the horizon is the limit. Genes flowed out of Asia and into the Americas. These "

― Adam Rutherford , A Brief History of Everyone Who Ever Lived: The Stories in Our Genes