“The Malthusian trap, at least at its extremely pure theoretical limits. Suppose you are one of the first rats introduced onto a pristine island. It is full of yummy plants and you live an idyllic life lounging about, eating, and composing great works of art.
You live a long life, mate, and have a dozen children. All of them have a dozen children, and so on. In a couple generations, the island has ten thousand rats and has reached its carrying capacity. Now there’s not enough food and space to go around, and a certain percent of each new generation dies in order to keep the population steady at ten thousand.
A certain sect of rats abandons art in order to devote more of their time to scrounging for survival. Each generation, a bit less of this sect dies than members of the mainstream, until after a while, no rat composes any art at all, and any sect of rats who try to bring it back will go extinct within a few generations.
In fact, it’s not just art. Any sect at all that is leaner, meaner, and more survivalist than the mainstream will eventually take over. If one sect of rats altruistically decides to limit its offspring to two per couple in order to decrease overpopulation, that sect will die out, swarmed out of existence by its more numerous enemies. If one sect of rats starts practicing cannibalism, and finds it gives them an advantage over their fellows, it will eventually take over and reach fixation.
If some rat scientists predict that depletion of the island’s nut stores is accelerating at a dangerous rate and they will soon be exhausted completely, a few sects of rats might try to limit their nut consumption to a sustainable level. Those rats will be outcompeted by their more selfish cousins. Eventually the nuts will be exhausted, most of the rats will die off, and the cycle will begin again. Any sect of rats advocating some action to stop the cycle will be outcompeted by their cousins for whom advocating anything is a waste of time that could be used to compete and consume.
For a bunch of reasons evolution is not quite as Malthusian as the ideal case, but it provides the prototype example we can apply to other things to see the underlying mechanism. From a god’s- eye-view, it’s easy to say the rats should maintain a comfortably low population. From within the system, each individual rat will follow its genetic imperative and the island will end up in an endless boom- bust cycle."
https://www.slatestarcodexabridged.com/Meditations-On-Moloch