Only a little side note really:
Charles and Emma Darwin had ten children, of whom seven survived to adulthood. Although only three provided Darwin with grandchildren,
You can see why people had large families…..if only 30% of your children provide you with grandchildren then you need a pretty good number just to keep the genes being passed on….
Erm – there’s the small matter of birth control (other than depriving one’s husband of his ‘conjugal rights’ 😉
That said, it’s also, as you’ve pointed out, the reason people tend to have fewer children as their standard of living goes up and more of their children survive.
Of course if he had not married his cousin, it might have helped.