Michael White looks at how travel has impacted human evolution:
Our species’ wanderlust has … had a profound impact on how we’ve experienced evolutionary change. Much of our genetic makeup is due to what geneticists call founder effects, meaning that our genes reflect the chance membership of the small band of colonists that we’ve descended from, rather than evolutionary pressure to adapt. The fact that Scots commonly have red hair, while Norwegians have blond hair is likely due to founder effects and not because red hair is better suited to the Scottish climate. Our long tradition of pulling up stakes and seeking our fortunes elsewhere has also had the effect of putting the brakes on natural selection in many cases. One research team studied the fate of seemingly favorable mutations worldwide and concluded that human “populations may be too mobile, or their identities too fluid” for advantageous mutations to spread completely through a population. By moving around so much, we stir up the human gene pool and alter how evolutionary pressures act on our genes.