There's plenty of evidence across nature to support the idea that population sizes are controlled by resources. Farmer's spot this one easily. Rabbits and locusts peak in numbers one year, over-populate and die off so the following year there are fewer.
We humans can't be much different. We move to where the food and water are. Lots of water and food allows for high population count. A country like Australia can't support high population because we don't have lots of food and water, and we can't really eat coal and iron.
I don't think that we are really capable of restraining ourselves on a large scale. We consume a lot, not just food and water. The pragmatist in me thinks its inevitable that we'll all go to war with each other to secure food and water. The Christian in me hopes that we can avoid that war by making love real and sharing more equally those basics for life.