This essay is the fourth chapter in a larger project aimed at updating my knowledge, analysis and views on global population dynamics. This chapter describes and analyses one of the two major drivers of falling fertility during the demographic transition, the quantum effect. Specifically, this is the process by which economic and technological development drives a shift in the demand for offspring quality at the expense of quantity. The initial version of this text was published in July 2022, with an updated layout in October 2022. Updated versions might follow, and will be available here.