Every human population on Earth descends from people who moved, yet migration across borders is less common than headlines suggest. About 3.6 percent of the world's people live outside the country where they were born, roughly 281 million in the United Nations' 2020 estimate. The great majority of humans spend their lives in the country of their birth, and most people who move do so within their own country, from village to city or from one region to another. Most international migrants, too, travel through legal channels for work, study or family, not on boats or across deserts.

Push and pull

The oldest framework for thinking about migration came from the geographer Ernst Georg Ravenstein, who in the 1880s used British census data to propose a set of "laws of migration." Among his findings: most migrants travel short distances, and big cities grow by drawing people in from the countryside. In 1966 the demographer Everett Lee turned these observations into a model that is still taught. People weigh push factors, such as poverty, violence or persecution at home, against pull factors, such as jobs, higher wages, safety or relatives abroad. Lee added a third element that is easy to forget: intervening obstacles, such as distance, cost, borders and visa rules, which stand between wanting to move and actually moving. Personal factors matter too. Age, health, temperament and family ties make the same push feel unbearable to one person and tolerable to a neighbour.

Why the poorest rarely move far

A simple push and pull story predicts that the poorest people would migrate most, since they have the most to gain. The evidence says otherwise. Crossing an ocean or a border costs money, information and contacts. Researchers describe a migration hump: as a very poor country grows richer, emigration usually rises at first and falls only later, once incomes at home approach those abroad. Development, in other words, has tended to increase emigration in the short run rather than reduce it. Some recent studies question how well this pattern, drawn mostly from comparisons across countries, holds within a single country over time, so treat it as a strong tendency rather than a law. It matters for policy, because foreign aid is sometimes promoted as a way to keep people at home.

Families and networks

Economists first modeled migration as an individual choice: a worker compares wages here and there, subtracts the cost of moving, and goes if the gap is large enough. A later school, the new economics of labor migration, pointed out that the decision is often made by a household. A family may send one member abroad to spread risk across different sources of income, so that money sent home protects everyone if a harvest fails or a factory closes. Those transfers, called remittances, are a lifeline for many countries, and Level 6 returns to them.

Once some people from a town have moved, others follow. Migrant networks lower the cost and risk of moving by providing information, loans, housing and job leads. This helps explain why migrants from one Mexican state may cluster in one American city, or why villages in Kerala have sent workers to the same Gulf states for generations. Networks make migration self-sustaining, which is why flows often continue after the original push or pull has faded.

Categories and their limits

Governments sort migrants into categories: labor migrants, students, family members, refugees, irregular migrants. These labels matter enormously, because they decide who may enter and who may stay. Real lives are messier. A person may flee violence and also hope for work; a student may later marry and settle. Scholars use the term mixed migration for flows in which people with different motives and legal claims travel the same routes, often on the same boats. It helps to picture a spectrum running from fully voluntary moves to fully forced ones, with most journeys somewhere in between. Keeping the categories clear while remembering the people behind them is a task this course returns to again and again.

Worked example: a family in the Guatemalan highlands

Imagine a family that grows maize and a little coffee on a hillside plot in western Guatemala. Two dry years in a row cut the harvest, and coffee prices fall. A local gang begins demanding payments from shopkeepers in the nearby town. These are push factors: economic loss, climate stress and insecurity, tangled together.

The pull is concrete. A cousin already works in construction in Houston and says a job is waiting. Wages there are many times higher than anything available at home. The intervening obstacles are just as concrete: a long journey through Mexico, a smuggler's fee that can exceed the family's yearly income, and a border where most crossings without permission end in arrest.

The family does not send everyone. They borrow money and send their eldest son, who is young, healthy and unmarried. This is the household strategy described above: one member abroad spreads the family's risk. If he succeeds, remittances will repay the loan and buy fertilizer, school fees and perhaps a cinder block house. His success will also make it easier for a younger brother or a neighbour to follow, because the network now has one more link.

Is he an economic migrant or someone fleeing danger? Honestly, he is both, and that ambiguity is exactly what mixed migration means. Whether he may stay will depend less on his full story than on which legal category his case can be made to fit, a problem that runs through the rest of this course.