Thomas Malthus’ (1766-1834) was a modern realist whose theory was that population controlled itself through disease, war and famine. Further to that theory was the idea that without these checks and balances there would be no limit to the number of people we could produce. It’s an interesting cycle because according to the theory, if disease and war do not do their job, eventually we will reach a limit where there are more people than there are resources to support them and the population will collapse.
Essentially his belief was that if population was not controlled intentionally through birth control and abstinence, then they would be controlled by war and disease. Barring that, the population would exceed nature’s ability to support it and famine would result and with it would come the risk of extinction.
This scenario plays out in nature on a very regular basis. Imagine if you will, a large population of deer on an island. Without the intellect/ability to practice abstinence and birth control they cannot control their numbers artificially and so the population increases. Here we substitute accidents and predators for war to keep the numbers down and of course disease takes care of the rest. In a stable healthy herd (population) the numbers will remain more or less the same as healthy deer tend not to get sick and can outrun predators. Now take away the disease or the predators, or both. Suddenly you have a massive population explosion and only a limited amount of space and resources. A year, a decade, a century? Sooner or later there will be more deer than there will be food to feed them. Once that fails mass starvation ensues. This is the phase where extinction can occur. Overharvesting (eating grasses to the roots, killing trees by eating the bark and braches etc. can lead to total depletion of resources, meaning no new food growing to feed any survivors in future seasons. If you give 10 people only one bite of food, sooner or later all of them starve to death and there is no one left to start over. If there is not sufficient breeding stock left after the crisis, then the herd will fail and there will be no more deer on the island extinction.
Malthus’ theory expanded this observed fact of nature and applied it to the human population. Is Aids a population control? You betcha! All diseases are forms of population control to ensure a balance of numbers and the strength of the “herd”. Though we are at the top of our food chain, to nature we are just another animal in just another herd over-consuming the resources of a bigger island. We are subject to the same rules and face the same checks and balances with the same risks.