Well, there are several billion people now. At some point will reach capacity.
One interesting side note on population growth is that people slow down breeding when a sufficient number of the kids of their generation live to make a new generation. Starvation seems to act as a stimulent to large families. As does war.
Adam Smith noted that in poorer areas there were always many kids, but few made it to adult hood. It was not rare in his time for a woman in Scotland to bear 20 kids, and see one reach marriageable age and have children of their own. The situation in Ireland was comparable, but there a woman could have 20 kids, and have none survive. In England, families were smaller, but survival rates were higher, and among the rich, large families were very rare.
So if you want to slow down population growth, the answer is better nutrition. And fewer wars.
The 1920s saw huge families all over. The 1930s, families were small. Again, after the last world war, there were huge families to replace those that had been killed off, but by 1960, families started to taper, and by the 1980s the big bump in births was mostly due to children of the baby boom having their own small families.
