From the dawn of mankind to the turn of the nineteenth century, world population grew to a total of one billion people. During much of the nineteenth and twentieth centuries, human numbers have increased at increasingly higher rates, and we approach the new millenium in a world populated by nearly 6 billion people.

Population growth has continued throughout the past three decades in spite of the decline in fertility rates that began in many developing countries in the late 1970s, and in spite of the toll taken by the HIV/ AIDS pandemic in some countries. While the rate of increase is slowing, in absolute terms world population growth continues to be substantial.