Fertility Transition and Migration Transition: MCAT Demography Review

The demographic transition tracks birth and death rates through stages. Two related ideas show up in the same MCAT passages: the fertility transition (a shift to lower birth rates) and the migration transition (a shift in how people move as a society develops). Both are "what changes, and why" questions.

Fertility transition

The fertility transition is the period when a population's fertility falls from high to low levels. In the demographic transition model it corresponds to Stage 3: death rates are already low, birth rates start to fall, and growth slows.

Commonly cited drivers:

• Falling child mortality, so parents need fewer births to have the family size they want.
• Education, especially for women, and more women in paid work.
• Urbanization, where children cost more and contribute less to household income.
• Access to contraception and family planning.
• Changing norms and economic incentives around family size.

A useful number is replacement-level fertility, about 2.1 children per woman in low-mortality countries. Below that, a population shrinks over time without migration.

Migration transition

The migration transition model proposes that patterns of movement change as a country develops. In the early stages, rural people move toward cities (internal migration). As incomes rise and the population is growing quickly, emigration can increase. Later, as the country develops and birth rates fall, emigration slows and the country may become a net destination for immigrants. Different textbooks place the peak of emigration at different points, usually in the middle stages of the demographic transition (Stage 2 to 3), so read the passage's wording closely.

Terms for movement

• Immigration: moving into a country; emigration: moving out.
• Net migration: immigrants minus emigrants.
• Push factors: conditions that drive people away, such as conflict, poverty or lack of jobs.
• Pull factors: conditions that attract people, such as jobs, safety or family ties.
• Internal migration: moving within a country, such as rural-to-urban.

How they combine

Common traps

• Mixing up the fertility transition with the whole demographic transition. Fertility is one part of it.
• Assuming one correct peak for migration. The model is a pattern, not a law; passages specify their own.
• Confusing immigration and emigration. Immigrants arrive; emigrants leave.
• Using the total fertility rate as a birth rate. The birth rate is births per 1,000 people; fertility is per woman.

One-minute recap

• The fertility transition is the drop from high to low fertility, tied to Stage 3.
• The migration transition links development level to who moves and where.
• Push and pull factors explain individual decisions.