wealth
our wealth, or equivalently our standard of living, is ultimately related to how much time we have to spend taking care of the necessities: food, shelter, clothing. i've made the assertion several times that adding more people will lower our wealth. suppose we spend 10% of our time securing necessities. or looking at it a different way, 10% of our population grows food, builds houses, makes clothes. if we add 100 people then approximately 10 of them need to grow food. people can specialize so 10 people are more than 10 times as efficient as 1 person. so we need fewer than 10 growing food. but enter the law of diminishing returns. food production is also limited by available resources like arable land, fertilizer, fuel, etc. eventually the diminished return from limited resources overwhelms the efficiency gains of specialization. and we need more than 10 growing food. and down goes our wealth. how this applies to 21st century united states depends on where you think we are on the specialization vs resource curve. obviously i think we're racing along the brink.