To save others from having to google it, the >2.0 rate (cited various places as a range, roughly 2.07-2.1) is due to two things: 1. The birth rate for males is

To save others from having to google it, the >2.0 rate (cited various places as a range, roughly 2.07-2.1) is due to two things: 1. The birth rate for males is usually (always?) slightly higher than for females, roughly 105:100, and the fertility rate for a stable population is the average number of children a woman has to have to replace herself, so the ratio disparity makes the needed replacement fertility rate slightly more than two. 2. Not all females survive and remain fertile through their child-bearing years. There are various environmental factors thought to cause variations in sex ratios by way of slight hormone variations, so one shouldn't expect the male:female ratio to be constant from region to region. Medical care and disease and mortality rates vary, too. So there's no single exact fertility rate for a stable population, but it's roughly 2.07-2.10 for developed countries.