Humanity at the Crossroads
Maximum welfare, not maximum population, is our human objective.
-- Arnold Toynbee, Man and hunger, 1963
The maximum size the human population can attain is determined by the physical capacity of Earth to support people. This capacity, as discussed earlier, is determined by such diverse factors as land area; availability of resources such as energy, minerals, and water; levels of technology; potential for food production; and ability of biological systems to absorb civilization's wastes without breakdowns that would deprive mankind of essential environmental services. Of course, no one knows exactly what the maximum carrying capacity of Earth is; it would certainly vary from time to time in any case. Presumably, the capacity would be sustainable at a very high level for a short period by means of rapid consumption of nonrenewable resources. In the longer term, a lower capacity would be determined by the rate of replenishment of renewable resources and the accomplishments of technology in employing very common materials. Whatever the maximum sustainable human population may be, however, few thoughtful people would argue that the maximum population could be the same as the optimum. The maximum implies the barest level of subsistence for all. Unless sheer quantity of human beings is seen as the ultimate good, this situation certainly cannot be considered optimal.
The minimum size of the human population, on the other hand, is that of the smallest group that can reproduce itself. Like the maximum, the minimum size is also not the optimum. It would be too small to permit the