"Starvation, social strife, and disease interact in complex ways. If famine were the sole mechanism of collapse, the species might become extinct quite suddenly. A population that grows in response to abundant but finite resources, like the reindeer of St. Matthew Island, tends to exhaust these resources completely. By the time individuals discover that remaining resources will not be adequate for the next generation, the next generation has already been born. And in its struggle to survive, the last generation uses up every scrap, so that nothing remains that would sustain even a small population. But famine seldom acts alone. It is exacerbated by social strife, which [hinders] the production and [distribution] of food. And it weakens the natural defenses by which organisms fight off disease."