The world population has increased by 3 billion in 36 years. What is the reason?

1. First of all, the progress of medical technology and the improvement of sanitary conditions have greatly improved the survival rate of infants.

Secondly, the development of agricultural production and the increase of food supply enable people to get more food and nutrition, thus promoting population growth.

In addition, the improvement of education level and the improvement of women's status have slowed down the decline of fertility rate and also led to the increase of population.

Finally, with the promotion of social and economic development, people's living standards have improved and the demand for population growth has also increased. To sum up, the direct cause of the increase in the world population is the comprehensive effect of many factors such as the progress of medical technology, the development of agriculture, the improvement of education level and the development of social economy.