Population Size
Senior 3 · Biology
Population Size
Lesson 5 of 5
25 min
Rwanda has counted its people in five censuses. In 1978 there were 4.8 million Rwandans; in 2022 there were 13.2 million. The population almost tripled in 44 years, and over the same period the average density rose from 183 to 503 people per km². Humans are a population like any other, with births, deaths and migration, but we can change our own limiting factors: we grow more food, cure diseases and build cities. This lesson looks at what drives human population growth, and what it means for Rwanda.
Definition
Crude birth rate: the number of live births in a year for every 1,000 people in the population.
Crude death rate: the number of deaths in a year for every 1,000 people.
Rate of natural increase: the birth rate minus the death rate, usually given as a percentage: (with both rates per 1,000).
Total fertility rate (TFR): the average number of children a woman would have during her lifetime at present birth rates.
Life expectancy at birth: the average number of years a newborn baby can expect to live at present death rates.
| Year | Population | People per km² | Growth per year since the last census |
|---|---|---|---|
| 1978 | 4,831,527 | 183 | – |
| 1991 | 7,157,551 | 272 | 3.1% |
| 2002 | 8,128,553 | 321 | 1.2% |
| 2012 | 10,515,973 | 415 | 2.6% |
| 2022 | 13,246,394 | 503 | 2.3% |
Figure 1: Rwanda's population at each census (millions) with the time axis drawn to scale, and NISR's medium projection for 2052 (dashed).
The growth slowed sharply between 1991 and 2002. NISR explains that this reflects the high death toll of the 1990 war and the 1994 Genocide against the Tutsi. Growth then rose again, and has since slowed from 2.6% to 2.3% a year.
Worked example 1: growth between two censuses
Use the table. (a) By how many people did the population grow between 2012 and 2022? (b) Express this as a percentage increase. (c) Check that it agrees with a mean annual growth of 2.3%.
Note: 26% in ten years is not , because each year's growth is added to a bigger population, like compound interest.
| Indicator (NISR) | 1978 | 2022 |
|---|---|---|
| Total fertility rate (children per woman) | 8.6 | 3.6 |
| Crude death rate (per 1,000 people) | 17.1 | 6.3 |
| Life expectancy at birth (years) | 46 | 69.6 |
Worked example 2: natural increase and doubling time
The 2022 census found a crude birth rate of 27.8 per 1,000 and a crude death rate of 6.3 per 1,000. (a) Calculate the rate of natural increase. (b) Estimate how long the population would take to double if it kept growing at 2.3% a year, using the "rule of 70": . (c) NISR's medium projection is 23.6 million in 2052. Is that more or less than doubling? Suggest why.
| Area of life | Pressure from a growing population |
|---|---|
| Land and food | More people share the same land, so farms become smaller and are farmed more intensively; marshes and steep slopes are cultivated, raising the risk of soil erosion. |
| Forests and energy | In 2022, 76% of households cooked with firewood, so demand for wood and charcoal rises with the number of households. |
| Services | More classrooms, teachers, health centres, clean water and electricity are needed every year. |
| Jobs and housing | Many young people reach working age each year; towns grow quickly, and housing, transport and waste collection must keep up. |
| Nature | More waste and pollution, more pressure on wetlands and on protected areas such as national parks. |
A growing population also brings opportunities: a large, young workforce and a bigger market. What decides whether growth helps or harms is whether education, jobs, food production and services grow as fast as the population. Education matters here too: the 2022 census found a TFR of 3.4 for women with secondary education or above and 3.9 for women with primary education.
Warning
Common mistakes. (1) "Rwanda's population grows because the birth rate is rising": the birth rate is falling; the population grows because the death rate fell faster. (2) Multiplying the annual rate by the number of years: growth compounds (Worked example 1). (3) Quoting a figure without its year: population figures change, so always say which census or year they come from.
Overpopulation & Africa (Kurzgesagt – In a Nutshell). Watch for why falling death rates come before falling birth rates, and what makes fertility fall: health, education and development.
Tip
Exam technique. For "causes" answers, split them into falling death rate (health care, vaccination, food, clean water) and high birth rate (fertility, young population). For "consequences", give the resource under pressure and the effect: "more people need firewood, so more trees are cut".
Practice: human population growth
Key points
Further reading for this unit
Sources and credits
Written by Ganzaa: Figure 1 (drawn from the NISR census figures), the tables, the worked examples and the practice questions.
