ABSTRACT
For thousands of years, the human population grew at a snail’s pace. It took over a million years to reach about 1 billion people by the beginning of the nineteenth century. But then the pace of population growth quickened: A second billion was added in the next 130 years, a third in the next 30 years, and the fourth billion in just 15 years (McNamara, 1992). By the 1990s, there were more than 5 billion people on the planet. In early October 1999 human baby number 6 billion was born, most likely in a poor nation, and by 2009 there were 6.8+ billion people in the world (Gelbard et al., 1999; Population Reference Bureau, 2009). See Figure 5.1.
