The economics of hunting and gathering must have driven the biological evolution of human characteristics, since hunter-gatherer societies prevailed for the two million years of human history. These societies feature huge intergenerational resource flows, suggesting that these resource flows should replace fertility as the key demographic consideration. It is then theoretically expected that life expectancy and brain size would increase simultaneously, as apparently occurred during our evolutionary history. The brain here is considered as a direct form of bodily investment, but also crucially as facilitating further indirect investment by means of learning-by-doing.
Robson, Arthur J. and Hillard S. Kaplan.
2003."The Evolution of Human Life Expectancy and Intelligence in Hunter-Gatherer Economies ."American Economic Review,
93(1): 150-169.DOI: 10.1257/000282803321455205