Definition
The migration-fertility pattern is the well-documented demographic finding that women who migrate from higher-fertility regions to lower-fertility ones tend, on average, to have fewer children than they would have had if they had stayed — often fewer than the destination-born population of the same age and class.
The pattern shows up across very different migrations: Southern Black women moving to Northern U.S. cities in the twentieth century, rural Chinese women moving to Shenzhen, Turkish women moving to West Germany. Demographers debate the relative weights of three explanations — selection (the women who move are different to begin with), adaptation (the destination's lower-fertility norms take hold), and disruption (the act of moving postpones family formation) — but agree that the pattern itself is robust.
Why it matters
How it works
The three competing explanations each have evidence. Selection says the women who choose to migrate are atypical of their origin — more ambitious, more educated, more career-oriented — and would have had fewer children anyway. Adaptation says that whatever the migrant's starting preferences, exposure to the destination's lower-fertility norms (more education for women, more expensive child-rearing, contraceptive availability) pulls fertility down over time. Disruption says the act of moving itself — separation from partner during the move, instability in housing and employment, delayed marriage — postpones childbearing in ways that compound across the life course.
In the U.S. Great Migration, fertility data show all three effects. The first-wave migrants (1915–1929) tended to be younger and to migrate before marriage, which compressed marriage formation. Adaptation effects appeared over the subsequent decade as migrant women adopted the smaller-family norms of Northern Black middle-class neighborhoods. Selection effects are visible in the earliest cohorts — Black women who migrated north in 1915–1920 had fewer children than the Southern Black women who stayed, even controlling for age and education.
The consequence is that migration produces, paradoxically, fewer descendants than the same women would have produced at home. For the migrating group as a whole, this means the destination community grows more slowly than the inflow alone would suggest. For the individual migrant, it can mean a smaller family than she or her parents would have hoped for — one of the quieter migration losses.