Also, many other factors must be considered when estimating the earth"s capacity by any of the above definitions. For instance, one must consider the level of prosperity of the people, the technology available, and the distribution of available wealth. Under certain conditions, the world might not easily hold even 1 billion people, while under other conditions a number as high as 20 billion is possible.

             Another factor in overpopulation that must be considered is that of life expectancy. According to United Nations estimates, the life expectancy in developed nations in the 1950"s was approximately 66.0 years, while third world nations enjoyed a life expectancy of 40.7 years. Due to substantial declines in infant mortality, the average life expectancy in developed nations was 74.0 years and 64.7 years in developing countries. However, although the majority of this increase is due to decreases in infant mortality, jumps with this large of an increase cannot be entirely explained by that alone. New developments in medicine and technology have increased life spans across the board.

             Even more promising, and perhaps alarming, is the fact that predicted "upper limits" of human life expectancy have regularly been surpassed, and increases in life expectancy even appear to be accelerating. These average life expectancy increases, if they continue, will allow the world population to skyrocket at an even faster rate.

             Finally, and perhaps the most important issue that must be discussed in the debate on overpopulation is the issue of resource scarcity. So called "experts" love to enter the debate and make doomsday predictions that the world will run out of food, or oil, much like Dr. Paul Ehrlich did in his book, The Population Bomb. However, these predictions never seem to come true.

             Julian Simon, an economist, has an idea about natural resources which has sparked mountains of debate from both camps in the overpopulation discussion.