When a species overpopulates, the strongest and most efficient survive the problem. One way to be more efficient is to put less energy into reproduction. This mechanism explains why predators reproduce at much lower rates than their prey. Instincts that are not adaptive to a situation die out for lack of energy efficiency. With people, no individual or tiny group is fit to survive, so survival in humans is a function of the efficiency of a society.
Society needs to work with the coordination and strength of a single well trained body.
Your stomach doesn't argue prices with your liver, and so on, when you are strong and healthy. Things are shared equally, organs take what they need and no more. You figure the energy efficiency of activities, and the energy balance, if it is calculated right it works, you don't need to repeat the calculations over and over, but you can just do things over and over. Energy measurement is reliable. You can count on a calorie to be a calorie today and tomorrow and a million years from now, as far as anyone can tell.