Population age and sex structures have extensive consequences on development. Young populations require schools, older populations require funds for retirement, and both need well-functioning health systems. A high proportion of working-aged adults can boost economic growth. More men/women in a population can lead to a shortage of marriage partners. So, when population structures diverge sub-nationally, the social and economic consequences will also be diverse within countries. Rural and urban inequalities are particularly striking, especially in low- and middle-income countries where the urban transition is not complete. This raises the question: “How diverse are rural and urban populations, and does internal migration lead to gaps in the sub-national populations?” In our new paper, published Population and Development Review, we examine the internal migration patterns across Africa, Asia, and Latin-America and the Caribbean over the last 50 years, and consider the role of migration in shaping rural and urban population structures.

Internal migration, a much more common phenomenon than international migration, can redistribute the population within countries. Typically, migration is concentrated in younger adult ages, which could potentially hollow out the population of one region, to the benefit (or disadvantage) of the other. Moreover, since these migrants are of reproductive ages, their move can shift the future births from their origin to destination. However, while in- or out-migration rates may be high, if they balance each other out, the populations in origin and destination will remain the same. We used census sample data to estimate rural-urban migration, in- and out-, and the balance between them, the net migration, for nine Asian countries, 19 African countries, and 17 Latin American countries. By standardizing and smoothing the migration rates we were able to estimate continent-level rural-urban net migration flows by age and sex. We used a macro approach—the continent level—to unpack the role of migration at key stages of the urban transition in large and stable countries, rather than national, context-specific cases.

To determine the relative effect of internal migration on populations, assuming fertility and mortality levels remain unchanged (at three different points in time since the 1970s), we examined the theoretical contribution of migration using stable population models. Somewhat contrary to expectations, considering the strong age and sex patterns of migration, we found that internal migration only marginally contributes to divergence in rural/urban population structure—with sex ratios and dependency ratios strikingly similar whether we account for migration or assume zero migration. This is not to say that migration has no effect at the national level in particular contexts. For instance, women and children may migrate, leaving rural areas in conflict zones.

We further found that net migration in Africa is negligible and does not contribute to an urban transition. Fertility stalls, and the wide gap between rural and urban sectors, appear to be most important in shaping the population structure, and gap between the sectors in Africa. In contrast, in Latin America net migration contributed significantly to urbanization from the 1970s through to the 2000s, while migration can be expected to speed up the urban transition in Asia, as proportions urban in most Asian countries are still relatively low. Yet urbanization is not inevitable in Asia, nor in Africa. The rural sector may remain large, due to differential fertility declines across rural and urban sectors. Moreover, people may choose to stay in the rural sector, are trapped within it, or decide to move there—suggesting opportunities exist there too, and that advocating for urbanization to drive national economic growth, may be misguided. Rather, investment and creation of opportunities in the rural sector remains important. This is not to keep the rural population from migrating, but to acknowledge the importance of the rural sector, especially with the potential for de-urbanization on the horizon.

This article is part of PDR’s forthcoming 50th anniversary special issue: Looking Backward, Looking Forward: Celebrating 50 Years of Population and Development Review.

November 18, 2024

By: Ashira Menashe-Oren and Philippe Bocquier

in From Our Journals