People who can afford to have all their basic needs met without worry have less children on average. See: population decline in advanced economies, especially

People who can afford to have all their basic needs met without worry have less children on average. See: population decline in advanced economies, especially Nordic countries and middle/upper middle class America. Humans are still animals that act on instinct, and our instinctive behavior is, when faced with dangerous short term threats, to reproduce en-masse. War torn countries are the best example of this, humans fall back to a mass quantity strategy for survival. But in a situation of resource abundance? People have less kids and invest more in each child.