Read the extract and answer the questions.
Population Size and Growth
The size of a population is determined by the number of people living in a given area at a given time. The growth of a population is influenced by various factors such as birth rate, death rate and migration. Birth rate is the number of live births per thousand people in a year. Death rate is the number of deaths per thousand people in a year. Migration is the movement of people from one place to another for various reasons such as employment, education, conflict, natural disasters, etc. Migration can be internal (within a country) or international (across countries). The difference between birth rate and death rate is called natural growth rate. The difference between natural growth rate and net migration (immigration minus emigration) is called actual growth rate.
The world population has increased rapidly in the last two centuries due to various factors such as improvements in health care, sanitation, nutrition, education, etc. that have reduced death rates and increased life expectancy. The world population was estimated to be around 1 billion in 1800. It reached 2 billion in 1930, 3 billion in 1960, 4 billion in 1974, 5 billion in 1987, 6 billion in 1999, and 7 billion in 2011. According to the United Nations estimates, the world population was 7.8 billion in mid-2020 and is projected to reach 8 billion by 2023, 9 billion by 2037 and 10 billion by 2057.
What are some of the factors that have contributed to the rapid increase of world population in the last two centuries? (1 mark)