8.1 Human populations
- Syllabus
- First assessment 2026
- Topic
- 8.1
- Level
- SL
Inputs Add People
Births and immigration add people to a population; a crude input rate makes the count comparable across populations of different sizes.
Use events ÷ total population × 1,000 when the question asks for a rate per 1,000 per year. Births happen inside the population; immigration crosses its boundary from outside.
25,000 births in 500,000 people gives (25,000 ÷ 500,000) × 1,000 = 50 births per 1,000 people.
50 per 1,000: (2,000 ÷ 40,000) × 1,000.
2,000 is an event count, not a rate. A rate needs the population denominator and its units.
Outputs Remove People
Deaths and emigration remove people from a population; their crude rates express those annual outputs per 1,000 residents.
Use the same events ÷ population × 1,000 calculation at town, country or global scale. A crude death rate describes the population’s current output, not an individual’s lifetime risk.
15,000 deaths among 750,000 people gives 20 deaths per 1,000 people for that year.
The smaller population: 50 versus 10 per 1,000.
Do not compare raw deaths without population size; that confuses a count with a rate.
Choose the Metric Before Calculating
Each population metric answers a different question: TFR describes births per woman, life expectancy describes expected years, natural increase compares birth and death rates, and doubling time estimates growth speed.
Use doubling time ≈ 70 ÷ growth rate (%) only after converting the growth rate to a percentage. Use natural increase = birth rate − death rate; if rates are per 1,000, divide the result by 10 to express a percent.
At 2% annual growth, doubling time is about 35 years; birth rate 30 and death rate 10 per 1,000 gives natural increase 20 per 1,000, or 2%.
Doubling time, not life expectancy or TFR; use 70 ÷ percentage growth.
Do not put a per-1,000 rate directly into 70 ÷ r; the formula expects percent units.
Projection Means ‘If’
The global human population has followed a rapid growth curve, but future projections are conditional scenarios rather than fixed predictions.
UN high, medium and low scenarios diverge mainly because different fertility assumptions compound across generations; mortality and migration assumptions also affect the path.
If fertility falls faster than assumed, the population path can move below an earlier medium scenario even though current population is unchanged.
Read each curve's fertility, mortality, migration and time assumptions, and treat the spread as evidence of uncertainty.
The middle scenario is not guaranteed, and uncertainty does not make every scenario equally plausible.
Direct Policies Name Their Target
Direct population policies explicitly target births or migration: anti-natalist policies seek fewer births, pro-natalist policies seek more births, and migration policies alter immigration or emigration.
| Named policy | Direct target | Measures and limits |
|---|---|---|
| China's one-child policy (1980–2016) | lower birth rate | restrictions and incentives reduced births but created rights and age-sex-structure concerns |
| Singapore's 'Stop at Two' (1972–87) | lower birth rate | family planning, smaller-family benefits and media changed fertility behaviour |
| Singapore's later 'Have three or more if you can afford it' | raise birth rate | maternity leave, childcare and child benefits sought more births, with limited response |
| skilled-worker immigration policy | raise selected immigration | fills labour gaps but changes age structure, rights and integration needs |
Evaluate intended rate, cultural and religious context, economic and social measures, rights, uptake, time lag and measured outcome.
Anti- or pro-natalist describes intent, not automatic success or ethical acceptability.
Change Conditions, Not Just Birth Rules
Indirect policies change economic, social, health or development conditions; these alter births, deaths or migration through intermediate choices and survival pathways rather than a population quota.
| Named example from the local textbook | Indirect pathway |
|---|---|
| Japan: compulsory primary education and universal health insurance | education and healthcare improve knowledge and survival, changing fertility decisions and lowering mortality |
| Singapore: subsidized childcare and maternity leave | welfare support changes the cost and feasibility of raising children, which may influence births without guaranteeing them |
Gender equality, education, sanitation, public health, pensions and welfare can act through different pathways; effects depend on access, culture, employment and time.
An indirect influence is probabilistic: improved education or welfare does not produce the same demographic result in every society.
Read Shape Before Explaining It
An age-sex pyramid is a snapshot of population composition: age groups run vertically, the two sexes sit on opposite sides, and width shows number or percentage.
Start with shape before causes. A broad base signals many young people; a wider upper section signals more older people. The diagram describes structure, not automatically a DTM stage or forecast.
A pyramid that narrows sharply above age 60 has fewer older people relative to the base; a column-like shape has more similar-sized age groups.
The population is relatively youthful; you cannot yet infer the cause or exact DTM stage.
Do not explain a pyramid’s cause before describing its axes and shape.
The Rate Gap Drives the Curve
DTM stages describe how birth and death rates change; the gap between those rates, not the stage label, determines whether population grows, stabilizes or declines.
Stage 1 has high births and deaths; in stage 2 deaths fall first, stage 3 births fall, stage 4 both are low, and stage 5 may have births below deaths. Use the rate sequence to explain the curve.
When deaths drop from 30 to 10 per 1,000 while births stay at 35, the gap widens and growth accelerates; later, falling births narrow the gap.
Stage 2 pattern: the death rate has fallen first, so the positive gap is large.
DTM stages are a generalized pattern, not a universal timetable every country follows identically.
Objective notes
8 learning objectives8.1.1Population inputs• Births and immigration• Crude birth rate, immigration rateView8.1.2Population outputs• Deaths and emigration are outputs from a human population• Crude death rate (number of deaths per 1,000 people in a population per year) and emigration rate (number of emigrants per 1• The rates can be used at a variety of scales—from small urban areas, like a town, to a country to a region or to the global populationView8.1.3Population dynamics metrics• Population dynamics can be quantified and analysed by calculating total fertility rate, life expectancy, doubling time and natural increase• Total fertility rate is the average number of births per woman of childbearing age• Life expectancy is the average number of years that a person can be expected to live, usually from birth, if demographic factors remain unchanged• Doubling time is the number of years it would take a population to double its size at its current growth rate; it can be calculated by using the rule of 70View8.1.4Global population growth models• The global human population has followed a rapid growth curve• Models are used to predict the growth of the future global human population• UN projection models indicate three scenarios linked to future fertility rates• There is uncertainty about how future human fertility rates may change, leading to the three scenarios in the modelsView8.1.5Direct population policies• Population and migration policies can be employed to directly manage growth rates of human populations• These may be anti-natalist or pro-natalist, thereby directly addressing birth rates, or they may address immigration and emigration• These policies may use a variety of cultural, religious, economic, social and political factors to achieve their aims• Include: named examplesView8.1.6Indirect population policies• Human population growth can also be managed indirectly through economic, social, health, development and other policies that have an impact on births, deaths or migration• Many development policies addressing areas such as, but not limited to, gender equality, education, improvements in public health and welfare will indirectly affect births• Include: two named examplesView8.1.7Age-sex pyramids• The composition of human populations can be modelled and compared using age–sex pyramids• The pyramid is measured in absolute numbers or as a percentage of the total population• It shows the proportion of the population of either gender in each age groupView8.1.8Demographic transition model• DTM describes changing birth and death rates through stages of development• Used to analyse population change over timeView