I should have said increased age at first birth. It’s a simple matter of demographic progression. As a population ages, the rate of age related diseases increases.
If the age of first birth increases (as it has), then age related birth problems will also increase.
It is also true that having “simple” members of the family was far more common (and accepted) in previous eras. Our society no longer accepts that idea willingly, partly because if you are going to limit your offspring to two, you want them to be perfect and partly because feminist culture doesn’t want to admit that certain choices have predictable consequences.
“I should have said increased age at first birth.”
What difference would that make if the ‘difference’ weren’t itself environmental in origin?