World population is currently forecasted to reach 11 billion by the end of the century before leveling off. Most of this future growth will be concentrated in the developing countries of Africa, Asia, and Latin America, where the need to reduce poverty without harming the environment will be particularly acute. Furthermore, despite shrill protests to the contrary by ultra-conservative free market advocates, The need for most necessities of human life are driven more by population that per-capita income. Demands for housing, food energy and arable land, freshwater, and industrially fixed nitrogen are more sensitive to the growth of human population than to the growth of per capita income or even to recent changes in technological efficiency. The more people there are, the more thinly natural resources get spread—at any price or income—and the more significant the environmental and social costs of producing them. As these resources diminish, more conflict over their distribution can be expected, and clashes between the Haves and the Have-Not’s can be expected to be more frequent and bloody.

Over a century ago, Thomas Malthus predicted that exponentially rising populations would quickly outstrip linear increases in economic productivity, and thus make famine and social catastrophe for Have-Not’s inevitable. Coming as they did in the early years of the Industrial Revolution, his words were a great comfort to business owners and capitalists who sought freedom from the moral implications of many practices that were profitable for them at the expense of poorer classes. Today, Malthus' methodologies have been widely criticized—particularly his failure to account for increasing productivity beyond mere linear rates. His depressing attitudes regarding the working and poor classes are also antiquated in an age when most developed nations have moved away from pure, unregulated laissez faire and there is a fair amount of economic trickle-down to working classes.

Even so, despite the flaws in Malthus' methods and conclusions, his suggestion that the Earth has a limited carrying capacity which can be exceeded by uncontrolled population growth is as valid today as ever. Some economists such as Julian Simon have challenged this notion in recent years. Simon, author of a book called "The Ultimate Resource" has argued that no resource will ever run out, but will simply become more and more difficult to extract, requiring economies to adjust accordingly. Thus, he says, the human race will never truly run out of anything it needs and population growth need not concern us. His arguments are based mainly on a confusion of infinity of scale with infinity of divisibility (i.e. Zeno's paradox) and a virtually limitless faith in the capabilities of human technology.

Simon's ideas have struck a resounding chord with ultra-conservative advocacy groups and the Religious Right—groups who’s first and foremost allegiance is to laissez faire worldviews more or less dressed up in Christian clothing, yet care enough about humanity to want desperately to avoid the consequences such views will ultimately have on the poor and the natural world. Those of this faith believe, largely out of personal worldview necessity, that the free markets which have so enriched them at comparatively little personal cost can enrich all others in like fashion—a noble wish, but one that quickly degenerates to mere wishful thinking. Though Simon's ideas have won the favor of these groups and generated numerous recycled copies of his ideas from within their ranks, they are flatly contradicted by an ever growing refereed scientific knowledge base in a wide range of relevant fields, and few scientists or economists today take him seriously.

How will burgeoning human populations affect the health of ecosystems? Is the loss of some species here and there simply a regrettable byproduct of human expansion? Or is the planet passing into a new and frightening epoch where the bottom could conceivably come out of our biosphere's stability in just a few human generations if nothing changes? These questions are now more important than ever, not only because time is of the essence, but because those who are in denial of them are growing number and political influence. If reason is to prevail, she must be given a voice.