After growing very slowly for most of human history, the world's population more than doubled in the last half century, crossing the six billion mark in late 1999. Furthermore, world population is still increasing by about 78 million people a year, despite the trend worldwide towards smaller families. Total population size is likely to continue to grow for at least the next 40 years and by at least another 1.5 billion people. Almost all of this growth is occurring in the developing regions, while most industrialised countries are growing very slowly or not at all, and in some countries the population size is even declining. However, these developed countries make up just one fifth of the world's population and consequently have little impact on demographic trends. This results in the need for investigation into the causes of high rates of population growth.…
