Human Population Dynamics (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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
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
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
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
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
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
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:
High-fertility scenario: assumes higher birth rates will continue, leading to a more rapid population increase
Medium-fertility scenario: assumes a steady decline in fertility rates, leading to moderate population growth (this is the most likely scenario)
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
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