Understanding Population Dynamics: Birth, Death, and Growth
Understanding Population Dynamics
The birth rate is the number of births in a population in a specific period. It is measured by the crude birth rate (CBR). The total fertility rate (TFR) is an estimate of the average number of children that a woman has during her lifetime. A minimum of 2.1 children per woman allows generational replacement to take place. However, in developed countries today, the rate is only 1.6 children per woman.
The death rate is the number of deaths in a population in a specific period. It is measured by the crude death rate (CDR). As a consequence of the fall in the death rate, there has been an increase in life expectancy. This is the average number of years that a person expects to live. Life expectancy in the world is about 70 years, but there are differences between women and men, and between different countries.
Natural population growth is the difference between births and deaths. If more people are born than die, the population increases, and vice versa. It is measured by the rate of natural increase (RNI). The total number of inhabitants in a place is used to calculate population density. This is the ratio between the number of people and the size of the area that they occupy.
20th Century Population Trends
In the 20th century, there was a rapid population growth (or the population explosion). The birth rate has fallen throughout the world. The fertility rate has also fallen. There has been a decline in the death rate in most regions. Life expectancy has risen because of advances in medicine, nutrition, and hygiene.
Population Growth in Developed vs. Less Developed Countries
Developed countries have low population growth because these countries have low death rates and low birth rates.
Reasons for Declining Birth Rates
The birth rate has declined for the following reasons:
- There are more working women, who sometimes find it difficult to combine work and raising children.
- Contraception is widely available.
- Families delay having children.
- It is expensive to raise a family.
- Social values are changing.
Less developed countries have more dynamic populations. The birth rate in these regions is very high:
- Infant mortality rates are high. Women have more children if they think that some of them may die.
- Many families work in agriculture. Their children work too and contribute to the family income.
- Some religions are opposed to the use of contraceptives.
In countries where governments implement family planning policies, the birth rate is usually lower. Life expectancy is low in less developed countries.
The Decline of the Fertility Rate
The number of children per woman has fallen all over the world:
- In developed countries, many women go out to work and wait longer to have their first child.
- In emerging and less developed countries, child mortality has fallen. Consequently, many families no longer need so many children for economic reasons.
The Increase in Life Expectancy
People now live longer than in the early 20th century. Today, life expectancy in developed countries is high: 78 years. Together with a low birth rate, this results in an ageing population. In developed countries, 17% of the population are aged 65 or over. The population is also growing older in some emerging countries. However, in less developed countries, life expectancy is low and the birth rate is high.
Generational replacement does not take place, so population falls. Governments need to spend more on health care, pensions, and retirement homes. Older people often have lower incomes and save more.