The late, great Julian Simon spent decades battling intellectually against biologists and zoologists who were convinced that human population growth, if governments did not hold it in check with draconian measures, would spell doom for multitudes of humans. (I might as well have used the present tense above, because many of the scientists with whom Simon did battle, including the most prominent, Paul Ehrlich, are still alive.) These students of animal development and behavior insist that every species inhabits an environment with a natural "carrying capacity." If the population of a species grows in number beyond the limits of its environment's carrying capacity, the death rate of members of that species will rise, while its members' birth rate falls, because species members will confront unusual difficulty gaining access to food, water, and shelter. The species' population is thus confined to the limits of its environment's carrying capacity by the brutality of uncaring na