All your diapers are belong to us!Before the advent of reliable contraception and relaxed social roles for women, pretty much everyone had lots of children. For the last two generations or so, children have been a choice, and families can grow according to their preferences. (Economics explain some, but not all, of people's family size choices, research finds.) [The History and Future of Birth Control: 12 Tales]
As a result, a new correlation has emerged: People from small families tend to have only a few kids, and people from large families tend have large broods. Kolk and his colleagues wanted to know what effect this correlation would have on the fertility rate in the long term.
Actually, I've been thinking about this on a personal level. This has certainly played out in my personal experience. I counted up 75 living direct descendants from my dad (he's is still alive). Family get-togethers can be huge! This was a shock to my wife when we first got married. On her side, a family of with two children was considered large with no children being the choice of many. She's the anomaly in her family now. And with fewer and fewer on her extended side remaining, finding heirs for property and someone to care for the elders has become an issue. And then I began thinking about what it might be like when I'm old and have grandchildren and great-grandchildren. That will great.