Most of that growth is believed to occur in developing nations. An eventual world population of 8-12 billion is expected by the end of the century, though estimates change frequently. Of the present 6 billion people worldwide, about half live in poverty and at least one fifth are severely undernourished. The rest live out their lives in comparative comfort and health (Kendall and Pimentel, 1994,p.200).
Malthus presented his well-known theory of population in 1798, which stated that whereas population grew in geometrical progression, food resources increased in arithmetical progression. Because of this, Malthus said, it was necessary to control population growth through 'preventive checks', which included moral restraint, late marriages etc. Malthus warned that if this was not done, then nature would apply its own crude methods (called 'positive checks' by Malthus) to reduce population from its higher level. These positive checks included epidemics, floods, earthquakes, droughts and other natural calamities. The theory presented by Malthus had created an alarm during his own lifetime. But later day economists criticized him sharply and called him false prophet', arguing that food produce no longer increased in arithmetical progression, as Malthus had claimed, since agricultural output could now be increased to any level, with the help of scientific methods of cultivation and modern technology. These economists, also, said that the use of contraceptives in modern times had made it possible to check population growth effectively. The 'preventive checks' and 'positive checks' introduced by Malthus had, therefore, now become irrelevant and obsolete, these economists argue (Pimentel et al, 1996, p.1-10)
A more modern and scientific theory of population, known as the optimum theory of population had received considerable appreciation from the present-day economists. It stated that, for every country, there was a certain optimum level of population, which, at a given point of time, was required to exploit and use its resources in the best possible manner. If the population were below the optimum level, the resources of the country would remain partly unexploited and unutilised. On the contrary, if the population was above the optimum level, a certain percentage, of the country's population was likely to remain unemployed. This theory was more realistic, since it took into consideration both the relevant factors namely a country's population and its resources. Moreover, it rightly acknowledged that neither a higher population was always a curse nor a lower population was always a blessing (Pimentel et al, 1994, p.350)
However, almost two centuries after Malthus, we presently find ourselves in a demographically divided world, one where national projections of population growth vary more widely than at any time in history. In some countries, population has stabilized or is declining; but in others, population is projected to double or even triple before stabilizing. In 32 countries, containing 14 percent of world population, population growth has stopped. By contrast, Ethiopia's population of 62 million is projected to more than triple to 213 million in 2050. Pakistan will go from 148 million to 357 million, surpassing the U.S.