Human Population Dynamics (HL IB ESS OLD COURSE - IGNORE)

Revision Note

Demographic Variables

Inputs to human populations: births and immigration

  • Births and immigration are inputs that contribute to the growth of a population

  • Crude birth rate (CBR):

    • This is the number of live births per 1 000 people in a population per year

      • For example, a CBR of 15 means 15 babies are born for every 1 000 people in that population each year

    • CBR is calculated by dividing the total number of live births in a year by the total population and then multiplying by 1 000

C B R equals fraction numerator t o t a l space n u m b e r space o f space l i v e space b i r t h s over denominator t o t a l space p o p u l a t i o n end fraction cross times 1 space 000

Worked Example

A country has 25 000 live births in a year, and the total population is 500 000.

Calculate the crude birth rate.

Answer

CBR = (number of live births / total population) x 1 000

CBR = (25 000 / 500 000) x 1 000

CBR = 50 births per 1 000 individuals

  • Immigration rate:

    • This is the number of immigrants per 1 000 people in a population per year

Outputs from human populations: deaths and emigration

  • Deaths and emigration are outputs that reduce the size of a population

  • Crude death rate (CDR):

    • This is the number of deaths per 1 000 people in a population per year

      • For example, a CDR of 8 means 8 people die for every 1 000 people in that population each year

    • CDR is calculated by dividing the total number of deaths in a year by the total population and then multiplying by 1 000

C B R equals fraction numerator t o t a l space n u m b e r space o f space d e a t h s over denominator t o t a l space p o p u l a t i o n end fraction cross times 1 space 000

Worked Example

In a given year, a country recorded 15 000 deaths, and the total population is 750 000.

Calculate the crude death rate.

Answer

CDR = (number of deaths / total population) x 1 000

CDR = (15 000 / 750 000) x 1 000

CDR = 20 deaths per 1 000 individuals

  • Emigration rate:

    • This measures the number of people leaving a population per 1 000 people per year

Quantifying population dynamics

  • Population growth and decline can be quantified through several key measures:

  • Total fertility rate (TFR):

    • This is the average number of children a woman is expected to have during her lifetime, based on current age-specific fertility rates

      • In developing countries, TFR tends to be higher (e.g. due to limited access to family planning)

    • TFR is calculated by summing the age-specific fertility rates (ASFR) and multiplying the result by five

T F R equals sum A S F R cross times 5

Worked Example

A country has the following fertility rates per 1 000 women in each age group:

  • 15-19 years: 20 births per 1 000 women

  • 20-24 years: 85 births per 1 000 women

  • 25-29 years: 100 births per 1 000 women

  • 30-34 years: 80 births per 1 000 women

  • 35-39 years: 40 births per 1 000 women

  • 40-44 years: 10 births per 1 000 women

  • 45-49 years: 2 births per 1 000 women

Calculate the total fertility rate.

Answer

TFR = (20 + 85 + 100 + 80 + 40 + 10 + 2) x 5

TFR = 1 685 births per 1 000 women

TFR = 1.685 children per woman

This means that, on average, a woman in this country is expected to have approximately 1.69 children over her lifetime based on current fertility rates.

  • Life expectancy:

    • This is the average number of years a person is expected to live from birth, assuming current demographic factors (such as healthcare) remain the same

  • Doubling time (DT):

    • This is the number of years it would take a population to double in size, based on its current growth rate

    • DT is calculated using the 'rule of 70': divide 70 by the population growth rate percentage

D T equals fraction numerator 70 over denominator g r o w t h space r a t e space percent sign end fraction

Worked Example

A population has a growth rate of 2% per year.

Calculate the doubling time.

Answer

DT = 70 / growth rate

DT = 70 / 2

DT = 35 years

  • Natural increase rate (NIR):

    • This is the difference between the crude birth rate and crude death rate, usually expressed as a percentage or a number per 1 000.

      • If the birth rate is higher than the death rate, natural increase occurs

    • NIR is calculated by subtracting the CDR from the CBR and then dividing the result by 10

N I R equals fraction numerator open parentheses C B R minus C D R close parentheses over denominator 10 end fraction

Worked Example

A country has a CBR of 25 births per 1 000 individuals and a CDR of 10 deaths per 1 000 individuals.

Calculate the natural increase rate.

Answer

NIR = (CBR - CDR) / 10

NIR = (25 - 10) / 10

NIR = 1.5%

Examiner Tips and Tricks

Make sure you can define terms like crude birth rate, fertility rate and life expectancy. These often come up in exam questions.

Human Population Growth

Rapid growth of the global human population

  • The global human population has followed a rapid growth curve, particularly in the past century

    • The global human population grew very slowly until 18th century

    • From 10 000 BCE to 1700 CE, the average growth rate was just 0.04% per year

    • There has been exponential growth in the global human population since the mid 18th century

    • In 1800, the world population was about 1 billion

    • By 2024, the population will have grown to over 8 billion

    • This growth is largely due to improvements in medicine, agriculture and technology, which have reduced death rates

  • The growth rate is starting to fall again

  • However, the world population is projected to continue to grow until approximately 2100, when it could reach more than 11 billion

Line graph showing world population growth rate from 1760 to 2100. Growth peaks at 2.1% in 1960, then declines to 0.1% by 2100. Population rises from 0.9B to 11.2B.
World population total and growth rate, 1750-2015 (with projections until 2100)

Models to predict future global population growth

  • Population models are used to predict the growth of the human population in the future

    • These models take into account birth rates, death rates, fertility rates, and migration

    • Models can help policymakers understand trends and make decisions about resource use, healthcare and urban planning

UN projection models

  • The United Nations (UN) uses models to project future global population growth, offering three different scenarios:

    1. High-fertility scenario: assumes higher birth rates will continue, leading to a more rapid population increase

    2. Medium-fertility scenario: assumes a steady decline in fertility rates, leading to moderate population growth (this is the most likely scenario)

    3. Low-fertility scenario: assumes fertility rates will drop significantly, leading to slower growth or a shrinking population

  • By 2100, the global population is projected to be around 9.7 billion in the medium-fertility scenario

Uncertainty of future fertility rates

  • Predicting fertility rates is challenging, leading to uncertainty in population forecasts

    • Changes in cultural norms, economic conditions, and government policies can all influence fertility rates

  • Countries that went through Industrial Revolutions in the 18th and 19th centuries experienced rapid population growth

    • Today those countries are developed and their growth rates have fallen

    • In some cases, they have fallen so much that their total populations are in decline (e.g. Japan)

  • The fastest population growth today occurs in developing countries that are rapidly industrialising

World map showing percentage change in population growth rate by country with a colour scale from red (-4%) to dark green (4%)
Global pattern of population growth rate (2021)

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