of children required to replace the parents. Under conditions of low mortality a 2.1 fertility rate should be sufficient. In 1992, the global fertility level was 3.4 children per woman. Thus, despite the fact that fertility in developing countries has declined by about one third since the 1960s (from an average of 6 children per woman to 4 per woman today), these regions may see their populations double in as few as 20 or 30 years ("Reproductive revolution" 1). Moreover, even if worldwide replacement level fertility is reached by the end of the decade, the globe's human population will still reach 9 billion before eventually leveling off. If replacement levels are not reached until the year 2080, human populations could reach 14 billion or more.
Each additional person added to the world's masses must share in the Earth's resources (Keyfitz 441 462). Increases in the demand for food, water, energy, and shelter often result in environmental degradation. The desire to limit such degradation has given rise to the concept of "sustainable development." Sustainable development can be defined as "meeting people's current needs while preserving nature's productive capacity for the future ("The environment" 1 31)." It thus advocates environmental protection as a means of ensuring the potential for long term economic viability. Unfortunately though, sustainable development is both expensive and politically challenging. This is because individual, community, national, and global interests are often in conflict with each other. This conflict has been called "the tragedy of the commons." It perhaps is best illustrated by what typically occurs around villages with communal grazing lands. Under such circumstances, the individuals who benefit most from the grazing lands are those who have the largest number of livestock. This leads to competition and overgrazing. When pastures eventually become degraded, no livestock can be fed....