IB Geography 1.2.1 Population Change and Demographic Transition Over Time Notes

Population Growth over Time: Rapid Growth Is Recent and Already Slowing

1. For most of human history the world population grew very slowly, because high birth rates were canceled out by high death rates, above all among infants.
2. Sustained growth began in the late eighteenth and nineteenth centuries, when better food supply, clean water and sanitation cut death rates in industrializing Europe.

1. The world population passed 8 billion on 15 November 2022, the date the UN Population Division named the Day of Eight Billion.
2. The UN put the total at 8.2 billion in 2024.
3. World Population Prospects 2024 projects a peak of about 10.3 billion in the mid-2080s, easing to roughly 10.2 billion by 2100.
4. The world crude birth rate in 2024 was 16.3 per 1,000 people (World Bank).

1. The world crude death rate that year was 7.6 per 1,000, so natural increase ran at about 0.87% a year.
2. Average fertility has fallen from 3.31 births per woman in 1990 to 2.25 in 2024 (UN World Population Prospects 2024).

1. India overtook China as the world's most populous country in 2023 (UN DESA).
2. The UN counts 63 countries and areas whose populations peaked before 2024, between them holding 28% of the world's people.
3. It projects populations to keep growing through 2054 in 126 countries, among them India, Indonesia, Nigeria, Pakistan and the United States.

Natural Increase: Births Minus Deaths, with Migration Left Out

1. Crude Birth Rate (CBR)
   1. The number of live births per 1,000 people per year.
   2. It is crude because it takes no account of how old the population is.
2. Crude Death Rate (CDR)
   1. The number of deaths per 1,000 people per year.
   2. It is also unadjusted for age structure, which makes it easy to misread.
3. Natural Increase
   1. Subtract the crude death rate from the crude birth rate.
   2. Divide the answer by 10 to express it as a percentage a year.

Natural increase (%) = (CBR - CDR) / 10

1. Nigeria in 2024 had a crude birth rate of 32.5 and a crude death rate of 11.6 per 1,000, giving natural increase of about 2.1% a year (World Bank).
2. Japan in the same year had a crude birth rate of 5.7 against a crude death rate of 13.3, giving natural decrease of about 0.8% a year.
3. Natural increase leaves migration out, so it is not the same thing as population change.
   1. A country with natural decrease can still grow where net migration is positive.
   2. Actual change is natural increase plus net migration, which is why the two are reported separately.

Fertility Rate: The Measure That Sets a Population's Direction

1. The replacement level is 2.1 births per woman, which the UN gives as the level needed to hold a population steady over the long run without migration.
   1. The figure sits above 2.0 to allow for girls who do not survive to childbearing age.
2. Fertility is now below 2.1 in more than half of all countries and areas (UN World Population Prospects 2024).
3. Nearly one fifth of countries record fertility below 1.4, a group that includes China, Italy, South Korea and Spain.
4. Over one country in ten still records four births or more per woman, mostly in sub-Saharan Africa.

What Moves a Country's Fertility Rate

1. Education and Employment of Women
   1. Where girls stay in school longer, first births tend to arrive later, which shortens the years spent bearing children.
   2. Paid work outside the home raises the earnings a woman gives up for each birth.
2. The Economic Role of Children
   1. In largely agricultural economies children contribute labor early, then support parents in old age.
   2. Where schooling is long and housing is expensive, each child costs more for longer.
3. Access to Contraception and Maternal Healthcare
   1. Nigeria's 2023-24 Demographic and Health Survey found 15% of currently married women using a modern method of contraception.
   2. Unmet demand for family planning keeps actual family size above the size women say they want.
4. Infant and Child Mortality
   1. Where many children die young, parents have more births to reach the family size they intend.
   2. Falling child mortality usually comes before falling fertility rather than alongside it.
5. Cultural and Religious Norms
   1. Expectations about the age of marriage and the right number of children shift slowly, so fertility can stay high after incomes rise.
   2. Nigeria's survey recorded 5.6 births per woman in rural areas against 3.9 in urban areas, a gap inside one country.

Fertility responds to the whole set of conditions above rather than to any single one.

Population Momentum: Growth Carries On After Fertility Falls

1. A population with a wide base has a large number of women entering their childbearing years at once.
2. Even at fewer births each, that many potential mothers produce a large absolute number of births.
3. Growth therefore continues for decades after fertility drops below 2.1, until those large young cohorts age out.

1. This is why fertility below replacement does not mean a shrinking population in the same year.
2. It also explains how 126 countries can be projected to grow to 2054 while more than half are already below replacement.

Life Expectancy: Rising Almost Everywhere, but Not Irreversibly

1. Global life expectancy at birth reached 73.3 years in 2024 (UN World Population Prospects 2024).
2. Japan's 2024 abridged life tables give 81.09 years for men and 87.13 years for women (Japan Ministry of Health, Labour and Welfare).
3. Nigeria's figure for 2024 was 54.6 years (World Bank).
4. Most of the historical gain came from fewer deaths in infancy and early childhood.
   1. Life expectancy at birth averages across all ages, so each death of a newborn pulls it down by a full lifetime.
   2. This is why infant mortality and child mortality track life expectancy so closely.

Why Women Generally Outlive Men

1. The world gap in 2024 was about five years, at 76.0 years for women against 71.1 for men (World Bank).
2. Japan's gap that year was wider, at 6.03 years.
3. Men are more exposed to occupational hazards in sectors such as mining, construction and fishing.
4. Men are far more likely to die in armed conflict, homicide or a road traffic collision.
5. Rates of heavy smoking and heavy drinking are higher among men in most countries.
   1. None of these is fixed, so the size of the gap varies between countries and moves over time.

Life Expectancy Can Fall

1. Botswana's life expectancy fell from 60.1 years in 1990 to 52.2 years in 2001 during the HIV and AIDS epidemic, before recovering (World Bank).
2. Armed conflict and the collapse of health services produce the same kind of reversal.
   1. A reversal that large undoes decades of gain, which any model assuming steady improvement will miss.

Population Structure: What the Shape of a Pyramid Tells You

1. The vertical axis carries age, normally in five year bands from 0-4 upwards.
2. The horizontal axis carries either the number of people or the percentage of the total population.
3. Males are plotted to the left of the centre line, females to the right.
4. Reading percentages lets you compare countries of very different size, which absolute numbers do not.
5. Constructing a pyramid takes four steps.
   1. Count the population in each five year age band, males and females separately.
   2. Convert every count to a percentage of the total population.
   3. Draw one horizontal bar per band, males extending left of the centre line and females right.
   4. Use the same scale on both sides, so the two halves can be read against each other.
6. Irregularities in the bars carry information of their own.
   1. A notch marks a cohort thinned by war, famine or epidemic, or a year of very few births.
   2. A bulge marks a baby boom working its way up the diagram as those people age.
   3. Bars much longer on the male side in the working ages point to labor in-migration.

Three Pyramid Shapes and What Produces Them

1. Expanding: A Wide Base Tapering Fast
   1. High fertility keeps each new cohort larger than the one above it, which widens the base.
   2. Concave sides show heavy mortality thinning each cohort as it ages.
   3. Nigeria fits this shape, with 41.0% of its population under 15 in 2024 (World Bank).
2. Stationary: Near Rectangular Sides
   1. Fertility close to replacement makes successive cohorts a similar size.
   2. Low mortality until old age keeps the sides almost vertical.
   3. Growth is slow, so the total population is roughly stable.
3. Contracting: A Narrow Base Under a Wide Middle
   1. Fertility below replacement makes each cohort smaller than the one above it.
   2. Long life expectancy keeps the upper bars wide, so the diagram looks top heavy.
   3. Japan fits this shape, with 29.8% of its population aged 65 or over in 2024 (World Bank).

Dependency Ratios: How to Calculate One and What It Hides

1. The total dependency ratio compares the two dependent age bands with the working age band.
2. Dependents are taken by convention as everyone aged 0 to 14 plus everyone aged 65 and over.

Total dependency ratio = ((people aged 0 to 14 + people aged 65 and over) / people aged 15 to 64) x 100

1. The answer is the number of dependents for every 100 people of working age.
2. Two component ratios come from the same age bands.
   1. The youth dependency ratio puts only the 0 to 14 band on the top of the fraction.
   2. The old age dependency ratio puts only the 65 and over band on the top.
3. World Bank age-structure data for 2024 allow Japan and Nigeria to be compared on the same basis.
4. Japan had 11.4% of its population aged 0 to 14, 58.8% aged 15 to 64 and 29.8% aged 65 or over.
   1. Adding 11.4 to 29.8 gives 41.2, which divided by 58.8 and multiplied by 100 gives 70 dependents per 100 workers.
5. Nigeria had 41.0% aged 0 to 14, 55.9% aged 15 to 64 and 3.1% aged 65 or over.
   1. Adding 41.0 to 3.1 gives 44.1, which divided by 55.9 and multiplied by 100 gives 79 dependents per 100 workers.

The Demographic Transition Model: A Description of How Rates Moved

1. Warren Thompson set out the first version in 1929, then Frank Notestein published the formulation that spread widely in 1945.
2. Both generalized from the recorded birth and death rates of countries that had already industrialized.
   1. The four-stage curve as textbooks draw it is modeled on the changing birth and death rates of England and Wales.
3. The graph plots three things against time.
   1. The crude birth rate and the crude death rate are read off the left hand axis in births or deaths per 1,000.
   2. Total population is read off a separate axis, usually the right hand one.
4. The vertical gap between the birth rate line and the death rate line is natural increase.
   1. Where the birth rate line sits above the death rate line, the population grows.
   2. Where the lines cross so that the death rate sits higher, the population falls by natural decrease.

The Five Stages: Death Rates Fall First, Birth Rates Follow

1. Stage 1: High Stationary
   1. Birth rates and death rates are both high.
   2. Both fluctuate sharply with harvests and epidemics.
   3. The two rates roughly cancel, so the population neither grows nor declines for long.
   4. Behind the high death rate sit poor sanitation, unreliable food supply, limited medicine and heavy infant mortality.
2. Stage 2: Early Expanding
   1. The death rate falls first, and falls fast.
   2. Clean water, sewerage, better nutrition and basic healthcare are the usual causes.
   3. The birth rate stays high because expectations about family size have not yet changed.
   4. The gap between the lines is at its widest, so natural increase is fastest in this stage.

1. Stage 3: Late Expanding
   1. The death rate is already low, so most of the movement now comes from the birth rate.
   2. Urbanization, longer schooling for girls, paid work for women and contraception all push births down.
   3. The population is still growing, though the rate of growth falls each year.
2. Stage 4: Low Stationary
   1. Birth rates and death rates are both low, so natural increase is close to zero.
   2. The population is large and roughly stable in size.
   3. The age structure has aged, because decades of low fertility leave a narrow base.
3. Stage 5: Declining
   1. The birth rate falls below the death rate, so natural change turns negative.
   2. Japan's 2024 rates of 5.7 births and 13.3 deaths per 1,000 sit in this position (World Bank).
   3. The original model had only four stages, with the fifth added later to describe countries where deaths now outnumber births.

Limits of the DTM: What the Model Leaves Out

1. The model was built from European data, so it records one region's experience rather than a law all countries must obey.
2. It contains no migration term at all.
   1. A country in stage 5 can still gain population through net immigration, so the model cannot predict actual population change.
   2. Emigration of young adults removes future parents, which drags birth rates down for reasons the model does not show.
3. The time axis carries no scale, so the model cannot say how long a country will stay in a stage.

Assumptions the Model Makes

1. It treats development as the driver of falling fertility, which risks reading a correlation as a single cause.
   1. Fertility has fallen below replacement in countries at very different income levels, so income alone does not explain the change.
   2. Family planning programmes, schooling for girls and the cost of housing act partly independently of national income.
2. Stage 5 was described from only a few decades of data, so its long run shape is not established.
3. The model assumes mortality only improves, which Botswana's fall from 60.1 to 52.2 years of life expectancy contradicts.
4. It also assumes the underlying data are reliable.
   1. Nigeria's last census was held in 2006 and counted about 140 million people, so every current Nigerian figure is a modeled estimate.
   2. Setting a survey estimate beside a registered figure, as when Nigeria's fertility rate is compared with Japan's, mixes two very different qualities of data.

Nigeria and Japan: Contrasting Paths Through the Demographic Transition

1. Nigeria and Japan show how the same demographic indicators can produce opposite population pressures when countries occupy different parts of the demographic transition.
2. Nigeria sits between late stage 2 and early stage 3 because mortality has fallen while fertility remains high, whereas Japan fits stage 5 in the five-stage model because deaths exceed births.

Nigeria: Falling Mortality, High Fertility and Youthful Momentum

1. DTM position: Nigeria's 2024 crude birth rate was 32.5 per 1,000 and its crude death rate was 11.6 per 1,000, producing natural increase of about 2.1% a year.
   1. Fertility is falling but remains high: the 2023–24 Demographic and Health Survey recorded 4.8 births per woman, down from 5.3 in 2018.
2. Mortality fell before fertility: improved child survival and healthcare reduced deaths while family-size expectations adjusted more slowly, widening the gap between births and deaths.
   1. Access and place shape fertility: only 15% of currently married women used a modern contraceptive method, while fertility averaged 5.6 births per woman in rural areas and 3.9 in urban areas.
3. Population momentum sustains growth: large cohorts are entering childbearing ages, so the absolute number of births can remain high even as the average number of births per woman falls.
4. The population structure is strongly youthful: 41.0% of the population was under 15 and only 3.1% was aged 65 or over in 2024.
   1. Dependency is concentrated among children: Nigeria had about 79 dependents per 100 working-age people, including roughly 73 children and 6 older people.
5. The immediate pressures are demand for schools, maternal and child healthcare, housing, transport and enough formal employment for each large cohort entering the labour force.
   1. The potential benefit is a demographic dividend, but it appears only if education, health, job creation and governance convert the growing working-age population into productive employment.
6. National averages conceal variation: the rural–urban fertility gap shows that different parts of Nigeria are moving through the transition at different speeds, while the absence of a census since 2006 makes current totals modelled estimates.

Japan: Very Low Fertility, Ageing and Natural Decrease

1. DTM position: Japan's 2024 crude birth rate was 5.7 per 1,000 and its crude death rate was 13.3 per 1,000, producing natural decrease of about 0.8% a year.
   1. Fertility is far below replacement: the total fertility rate reached a record-low 1.15 in 2024, when about 686,000 births were registered.
2. Several mechanisms reinforce low fertility: delayed marriage and childbearing, high housing and childcare costs, and difficulty combining long working hours with caring responsibilities reduce completed family size.
3. Population momentum now works in reverse: decades of low fertility mean fewer women enter childbearing ages, so births can keep falling even if the fertility rate later rises slightly.
4. The population structure is strongly aged: 29.8% of the population was aged 65 or over and 11.4% was under 15 in 2024.
   1. Dependency is concentrated among older people: Japan had about 70 dependents per 100 working-age people, including roughly 51 older people and 19 children.
5. The immediate pressures are a shrinking workforce, rising pension and healthcare costs, labour shortages and the loss of services from some rural communities.
   1. Policy choices include greater labour-force participation, automation, family support and immigration, but none can quickly reverse an age structure built over several decades.
6. A higher crude death rate does not mean poorer health: Japan's life expectancy remained about 81 years for men and 87 years for women, so the high death rate mainly reflects the large share of older people.

Direct Comparison: Similar Ratios, Opposite Planning Priorities

1. Population direction differs because Nigeria records many more births than deaths while Japan records more deaths than births.
2. Dependency composition differs even though the total ratios look similar, since Nigeria's dependents are mainly children whereas Japan's are mainly older people.
3. Public spending priorities therefore differ, with Nigeria needing rapid expansion of education and job creation while Japan must fund pensions, eldercare and productivity gains with a smaller workforce.
4. Age structure reinforces the contrast over time because Nigeria's large young cohorts sustain growth while Japan's small younger cohorts reduce the future number of parents.

1. The DTM describes these broad patterns but does not by itself explain policy, migration, gender relations or regional inequality, so stage labels must be justified with dated evidence and evaluated rather than treated as fixed categories.

Using Nigeria and Japan in an Extended Answer

1. Stage and mechanism: Name the DTM stage for each country and justify it with the birth and death rates that produce the population direction.
2. Evidence: Pair every figure with the demographic mechanism it demonstrates rather than presenting a list of statistics.
3. Comparison: Keep Nigeria and Japan as the same pair throughout the answer so each paragraph advances the contrast.
4. Evaluation: Add a limitation of the DTM or the underlying data after explaining what the contrast shows.