The interesting part is that it is only really going up in nations that have not yet the comfort-level of western civilizations. I don't have the exact numbers at hand but in most European countries, and I guess vast parts of the US too, the population is actually stagnant or even shrinking if immigration is not considered.
Meaning, if peoples culture does not change, but the avaiable food does - we get the "unwanted" result of the ugly word of overpopulation - or birth control. Which is ugly as hell, too.
Absolutely not. Fertility rates have been going down steadily for decades in every developed nation - when children are no longer a requirement to have someone that will care for you once you reach old age, fertility rates start to drop.
It happens. But not overnight. And being rich in children is not only viewed as retirement savings, there are other reasons too ... which might change with general development. But again, maybe not overnight. Which was the scenario I was talking about.