The population of the world grows according to two factors: birth rate and death rate. The relationship between these two is called the natural increase.
If birth rate is higher than death rate there will be a positive natural increase and the population will grow.
If birth rate is lower than death rate there will be a negative natural increase and the population will fall.
If birth rate and death rate are at a similar level the will be no natural increase.
Birth Rate - Death Rate = Natural Increase
Factors which control Birth Rates
Birth rates can change for a number of reasons. High birth rates occur in countries where large families are needed so that the children can work at an early age. Families often have large numbers of children so that will be someone around to look after the parents in their old age. Some religions ban the use of contraception, meaning that the birth rate is harder to control.
Birth rates fall due to improvements in health care, meaning that children are more likely to survive into old age. Women in many countries, especially in MEDC's, tend to get married later and have children later, as they want to establish a career first. More education in the use of contraceptives has also helped to slow birth rates. In some countries the birth rate has been artificially controlled by the law. China is the best example of a country which has tried this.
Factors which control Death Rates
Death rates are high in countries where there is poor health care, bad sanitation or insufficient food. Primarily these are less developed countries that do not have the money or expertise to improve the situation. These countries often have problems of disease.
Death rates primarily fall due to improvements in health care, including better access to it. A clean water supply and better sanitation means that the threat of disease also diminish.
The demographic transition model
The relationship between birth rate and death rate has been used to create a four stage model of a country's population change, called the demographic model. Countries which are described as being developed have reached Stage 4. The UK is one of these. Other countries are at different stages of their development, and therefore occupy different places on the model.
High birth rate (BR) and high death rate (DR), both around 35 per 1000. This means a relatively slow population growth. High BR due to no contraception and the need for large families. High BR due to diseases, poor health care, poor water quality, and a poor food supply. The UK was at this stage in the period upto 1750. Only a few remote indigenous tribes, in places such as the Amazon rainforest, exhibit these characteristics nowadays.
BR remains high, at around 35 per 1000, but DR falls to about 20 per 1000 by the end of the stage. The DR falls due to improvements in health care, sanitation and water quality. There is also increased access to medicines and food. The UK was in this period between 1750 and 1880. Countries such as Bangladesh, Libya and Nigeria are currently in this stage of their development.
BR falls rapidly to near 20 per 1000, and DR continues to slowly fall to around 15 per 1000. The fall in the BR is due to better access to contraception, more family planning education, working women getting married and having children later, less need for children as a labour source. DR continues to fall as health care improves further, and sanitation conditions improve. The UK was in this stage between 1880 and 1950. Countries passing through this stage at present include China and Argentina.
BR and DR low, at under 10 per 1000. Although there may be some annual fluctuations population growth is close to zero. The UK is in this stage at the moment, along with countries such as the United States and Japan.
It has been suggested that a new fifth stage should be added to the model, due to some countries, such as Sweden and France, having higher DR than BR, so that their populations are actually falling.
The composition of the population of a country can tell you a great deal about its development. The best way to look at this is by studying a population pyramid. This is basically back to back bar graphs, one showing the number of males, the other showing the number of females. The bars represent age bands of 5 year intervals.
Different shaped population pyramids indicate the stage of development that a certain country has reached. The differences between the population pyramids of MEDC's and LEDC's are covered in the next section.
Population pyramids can indicate the BR and DR of a country. For instance a country whose pyramid has a wide base has a high BR. If the numbers rapidly decrease, to form a triangular shaped pyramid, then there must also be a fairly high DR, and so the country is in either the first or second stage of development. A country in Stage four will have a relatively narrow base, and there will be similar numbers of people in all the bands up until 70, when the numbers will start to fall. This country would be one like the UK with good health care, and a high life expectancy.
Population pyramids can also show the percentage of the population, which is described as being "dependant". These are the groups of people who rely on the economically active members of society. Dependants are classified as those under working age (0 - 15 years old) and those who have retired (over 65). They rely on the working age group of people between 16 and 64.
Population pyramids can also show significant events. In Germany there are far more males between 20 and 35, than there are females of a similar age. This shows up quite clearly on a pyramid, and is due to the huge numbers of male immigrant workers that came into the country through the 1990's. They came to Germany to find work, and left their families at home in places such as Yugoslavia and Turkey.
Another type of event that can be traced easily on population pyramids, is the effect of war. Often this leads to large in-balances in the population, with far more women than men of fighting age remaining as the men have been killed in battle.
Population pyramids can be used to help planning for the future also, as they can used to project the percentages of certain age-groups in the population over the next 50 years. In this way plans can be introduced to cope with the forecast changes, such as the ageing population in the UK.
MEDC's VS LEDC's
More Economically Developed: Less Economically Developed: Narrow base to the pyramid, due to low BR. Wide base to the pyramid, due to high BR. This means that there is a high dependent young population. Constant numbers of people through all bands of working age. Numbers decrease as you go up the pyramid, forming the triangular shape of the pyramid. Large number of people over 65, which means that there is a high dependent elderly population. Few people over 65, means there is a very small dependent elderly population. High life expectancy, due to good medical care, means that there is a high percentage over 65. This also means that the pyramid is taller. Low life expectancy, poor health care. Low DR due to good health care. Low infant mortality rate, means that families have less children, but they usually survive to live a long life. High DR and infant mortality rate. Families have more children, as they are not sure how long they might survive. Females tend to live longer then males. Females tend to live longer then males.