Reply #5: Mathematics offers the answer, IMO.

[brokensymmetry]

It's called a predator-prey model, and uses differential equations. The classic model uses coyotes and rabbits. They start out at some point; the coyotes do what coyotes are prone to do and increase in number. The rabbits act according to their nature, but as the coyotes increase in number, the rabbits aren't able to continue increasing their population.

At some point, the rabbit population peaks, but the coyotes keep hunting. Thus the rabbit population crashes, leading to mass coyote starvation. Ultimately, there are few coyotes, and the rabbit population begins to increase again. This leads to a repeating cycle.

It may be that the lack of food (mass famine) will do this to human-kind. Or it may be that disease will accomplish the same end. (humans like to think of themselves as very effective predators, and so they are...but bacteria and viruses are quite adaptive. They're mutating even now; check out the research on AIDS and TB among others. And then there is that new disease, SARS...)

Perhaps the particulars don't matter. I suspect that the salient point is that external factors will adjust the population toward a more sustainable level. I doubt that human-kind will exercise the restraint to accomplish this on their own.

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