Genetic traces of mankind’s migrations

United colours: Some may fear immigration as a novel phenomenon endangering established cultural and ethnic units, but research has shown that humans have always migrated and mixed. A recent global study suggests that more than 94% of individuals have significantly mixed ancestry. The picture shows a scene from the Cowley Road Carnival at Oxford, UK. (Photo: Michael Gross.) Migration is one of the biggest political issues of our time. Voters in some affluent countries flock to the xenophobic parties of the right, including the Front National in France and UK Independence Party. Science, like other transnational endeavours, stands to lose out if antimigration sentiment gains political power, as happened in the Swiss referendum of 2014 (Curr. Biol. (2014) 24, R257–R259). Post-industrial societies like Germany typically have much too low reproduction rates to keep the demographics in a stable equilibrium. Significant influx would be needed to keep the economy and social structures going at the present level, but politicians fail to create positive immigration policies for fear of alienating voters. Even countries that were founded by immigrants displacing earlier populations, such as the US, experience strong anti-immigrant prejudice and shore up their borders to stem the influx of the less fortunate. On the other side of the wealth spectrum, in European nations like Bulgaria and across much of Africa and Latin America, the migration streams that worry the wealthy Europeans and North Americans are often registered as brain drain. The young, mobile, enterprising and ambitious leave their home countries because of the lack of opportunity, and many don’t return. Anti-immigrant prejudice often portrays the arrival of foreigners as a new and unusual phenomenon endangering the immutable equilibrium of the longestablished native population. Historical records show, however, that migration and mixing of populations has always happened. Now fine-grained studies of human population genetics confirm mankind’s inclination to migrate and mingle, and enable analyses of the highly complex populations resulting from historic and even prehistoric movements.