The population of the Japanese islands is a little over 126 million people, with a population density of 900 people per square mile. For comparison, the United States has a population density of 84 people per square mile and we’re already inhabiting even very marginal land. We’re crowded.
The Japs are dealing with their population congestion by losing interest in sex. Last year only 1 million babies were born, while 1.3 million people died. The result is that the population is declining and simultaneously aging, as the average person keeps getting older. This is one of Nature’s ways of dealing with overpopulation, but there are others.
On the Indonesian island of Flores a very small sized and small brained species of extinct human was found, along with pygmy elephant fossils. My guess is that as the ocean slowly rose the size of the island shrank along with it’s available food supply, and being smaller became a survival trait.
Commonly among animals, when one species increases it’s numbers it becomes a more plentiful food for other, predatory species. So the predators increase as the food species decreases and then some of the predators starve and die to balance the food chain once again. Among humans, we war on each other to take each others territory. Whether we will or not in the future is unknown but if we do, we’ll probably kill off a large portion of our numbers because disease and famine always follow in the wake of our wars and kill as many or more than combat does.
Or, we could go the Flores way. If we just keep multiplying, we may start becoming smaller. Another remedy would be to stop living long lives and go back to an average lifespan of 40 years like primitive man. Lastly, we could do like the Japanese are doing, and a lot of people in Europe as well, and just stop having children.
That looks to be the most likely scenario, as it’s the most developed nations that are experiencing the greatest reverse in population growth. At the rate the world is developing, it may only be another hundred years or so before the whole planet has reached pretty much a par on technological development, and the current population displacement through migration out of the unlivable, permanently arid or frozen regions is completed.
With political/social stability and an end to migration, the Japanese option for population control is probably the way we’ll go.