The wealthier and more educated a country gets, the fewer babies people have. Prosperity is the best contraceptive.
The primary engine behind the explosion in human numbers was the Industrial Revolution, which catalyzed the demographic transition. This transition model describes a shift from a society characterized by high birth rates and high death rates to one defined by low birth rates and low death rates. In the pre-industrial era, populations were stable because high fertility rates were offset by high mortality, particularly among infants. However, advancements in sanitation, medicine, and agriculture—such as the discovery of germ theory and the Green Revolution—dramatically lowered death rates. Initially, birth rates remained high, creating a "gap" where far more people were born than died. This gap resulted in the exponential growth witnessed throughout the 20th century. 8.1 trends in human population growth