Today, more people live outside the country of their birth than ever before—nearly 250 million, or 3% of the world's population. That's up from 79 million in 1960, and the rising tide is a challenge for locals as well as for migrants themselves.
Science helps us think more clearly about migration, in part by showing its deep roots. Researchers wielding powerful new methods have discovered ancient, hidden migrations that shaped today's populations. Go back far enough and almost all of us are immigrants, despite cherished stories of ethnic and national origins. Science can also aid the 21 million migrants today who are refugees from violence or famine, according to the United Nations. They need food, medicine, and shelter now, but in the long run it is their mental health that will be key to building new lives, as shown by a case study of the long-persecuted Yezidis. The success of these and other immigrants depends in part on whether new countries spurn or welcome them, and research is starting to show how to manage our long-standing biases against outsiders.
Science itself is one of the more itinerant professions, with many scientists crossing borders in search of opportunity. They are surprisingly hard to track, but a set of online records offers an unexpected way to find the most migratory among them. Their spirit of adventure suggests that as the world continues to shrink, the impulse to move is unlikely to fade.