In the comments of the last post, Dr. Bruce Charlton reminds us of the issue of growing female childless ness. Let's compare men and women on this. I list below the percent of people without any children. I limit the women to those ages 45 to 64, and ages 50 to 69 for men.
The percent of women with no kids almost doubled from 10.2 percent in the 1980s to 18.8 percent in 2010. Having no kids has also grown a bit among men. The childless numbers for men and women are pretty close to each other which fails to support the claim that men are much more variable in their fruitfulness than women.