A comprehensive revision for Cambridge AS Geography, chapter 4 Population, subchapter 4.1 Natural Increase.

1. ASGEOGRAPHYREVISION
POPULATION
4.1 NATURALINCREASE

2. KEYTERMSANDDEFINITIONS
Natural increase is the difference between the number of births and
the number of deaths in a given region.
Carrying capacity is the largest population that the resources of a given
environment can support.
Population momentum is the tendency for population growth to
continue beyond the time that replacement level fertility has been
achieved because of a relatively high concentration of people in the
childbearing years. This situation is due to past high fertility rates that
result in a large number of young people.
Crude birth rate (generally referred to as the ‘birth rate’) is the number
of births per thousand population in a given year. It is only a very broad
indicator as it does not take into account the age and sex distribution of
the population.

4. KEYTERMSANDDEFINITIONS
Fertility rate is the number of live births per 1000 women aged 15–49
years in a given year.
Total fertility rate is the average number of children that would be
born alive to a woman (or group of women) during her lifetime, if she
were to pass through her childbearing years conforming to the age-
specific fertility rates of a given year.
Replacement level fertility is the level at which each generation has
just enough children to replace themselves in the population. Although
the level varies for different populations, a total fertility rate of 2.12
children is usually considered as replacement level.
Crude death rate (generally referred to as the ‘death rate’) is the
number of deaths per thousand population in a given year. Again only a
broad indicator, as it is heavily influenced by the age structure of the
population.

6. KEYTERMSANDDEFINITIONS
Infant mortality rate is the number of deaths of infants under one year
of age per thousand live births in a given year.
Life expectancy (at birth) is the average number of years a person may
expect to live when born, assuming past trends continue.
Population structure is the composition of a population, the most
important elements of which are age and sex.
Population pyramid or age–sex pyramid is a bar chart, arranged
vertically, that shows the distribution of a population by age and sex.

8. KEYTERMSANDDEFINITIONS
Sex ratio is the number of males per 100 females in a population.
Dependency ratio is the ratio of the number of people under 15 and
over 64 years to those 15–64 years of age.
Youth dependency ratio is the ratio of the number of people 0–14 to
those 15–64 years of age.
Elderly dependency ratio is the ratio of the number of people 65 and
over to those 15–64 years of age.

9. TOPICSUMMARY
The first hominids appeared in Africa around 5 million years ago.
Global population reached 1 billion around the year 1800 and 6 billion
in 1999.
The highest ever global population growth rate was reached in the
early to mid-1960s.
The components of population change are fertility, mortality and
migration.
The factors affecting fertility can be grouped into four main categories:
demographic, social/cultural, economic and political.

11. TOPICSUMMARY
Fertility levels in most parts of the world have fallen faster than
previously expected, with an increasing number of countries below
replacement level fertility.
The crude birth rate and the crude death rate are very generalised
measures of the population of a country or region.
Age- (and gender-)specific measures of fertility and mortality provide
more accurate information.
The causes of death vary significantly between the developed and
developing worlds.
The infant mortality rate is frequently considered to be the most
sensitive indicator of socio-economic progress. It is likely that the life
expectancy gap between rich and poor countries will continue to
narrow in the future.

12. TOPICSUMMARY
The most studied aspects of population structure are age and sex.
Other aspects of population structure that can also be studied include
race, language, religion and social/occupational groups. Age and sex
structure is conventionally illustrated by the use of population
pyramids.
Population pyramids change significantly in shape as a country
progresses through demographic transition. In countries where there is
strong rural to urban migration, the population structures of the areas
affected can be markedly different.
The sex ratio is the number of males per 100 females in a population.
Dependants are people who are too young or too old to work. The
dependency ratio is the relationship between the working or
economically active population and the nonworking population.

13. ADDITIONALWORK
1. Find out in more detail about the advances in the Neolithic revolution that
stimulated population growth.
2. Suggest why we can be more certain about the accuracy of demographic
data from the nineteenth century onwards compared to the period before.
3. What do you think are the main factors responsible for the UK’s current
relatively low birth rate of approximately 13/1000?
4. Look at the latest World Population Data Sheet on the Population
Reference Bureau’s website (www.prb.org). Select three countries that you
feel reasonably fit each of stages 2, 3, 4 and 5 of the model of demographic
transition.
5. Find out how fertility has changed in the past 50 years in the country in
which you live.
6. Find out how the infant mortality rate has changed in the past 20 years in
one less economically developed country.

14. SUGGESTEDWEBSITES
www.prb.org – Population Reference Bureau
www.unfpa – United Nations Population Fund
www.un.org/popin – United Nations Population Information Network
www.worldpopulationbalance.org