People have lived on earth for at least 2 million years. For most of that time, population size remained steady, because the number of people born roughly equalled the number that died. Disease and famine ensured that the size of the population did not overtake supplies of food and other resources. However, as farming methods became more efficient and medical knowledge improved, population size rapidly began to increase. It now stands in excess of 6 billion people, with more than one million babies born every four days. In many parts of the world, rapid population growth has created serious problems, such as food shortages and overcrowding in cities.
People are not evenly distributed among the world’s continents. The fact that a continent is large, such as North America, does not necessarily mean that it has a large population. Some regions cannot support more than a few people, while others, with fertile soils and good communications, can support many. The world map below shows the average number of people who live in a square mile, or kilometer, in each country. This is called population density.
The number of babies a woman has varies from one country to another. In the Sudan, above, the birth rate is high, with an average of 4.9 babies per mother. Better health care, even in the poorer countries of the world, means that fewer babies now die of hunger or disease, and fewer women die in childbirth. In wealthy countries, such as Canada, the birth rate is low because people can choose to have small families. Advances in medical knowledge also mean that people are living longer.