Thanks to a decrease in infant mortality, an increase in medical advances, and a huge increase in agricultural productivity, the 20th century saw the largest increase in human population in history. It took over 120 years for the world’s population to increase from one billion to two billion, but only 85 years (1927-2011) to reach almost seven billion.
Although overall population is growing, the rate of growth is declining and currently stands at about 1.1%, compared to a peak of 2.2% in 1963. Moreover, the countries which have reached the highest levels of development generally have the slowest rates of growth.
Wikipedia: World Population