I seriously doubt that there were that many grandmothers around until the great medical developments of the late nineteenth century, particularly in gyencology, that, for the first itme in human history, alowed most women to bear children without running as much risk of death or permanent injury as men going to war.
A good example is the many wives of Phillip II of Spain, the Armada king. He had somewhere between 6 and 8, none of whom was murdered as were two of the 6 wives of Henry VIII of England. Nevertheless, nearly all of Phililp’s wives, in spite of the best efforts of sixteenth century medicine (!!!), died either of childbirth or related complications.
The theory is a generalization.
So, what would happen to the children if Mom died in childbirth — they'd probably die too or wouldn't survive long. No offspring.
Wonder how much genetics contributed to survivable births? Probably some but not all.
Anyway, if Mom survived, she probably wouldn't have the risks of fighting or hunting. Both of which could result in serious injuries and shortened life.
Don't know. But it was an interesting theory.
By the early 1700s most of my female ancestors were living into old age. The 1600s were hard on them - early colonial New England had crowding, hunger and Indian attacks. Prosperity came in the 1700s with long life. As Massachusetts filled up, you got crowding, TB and dysentery.
Somewhere between one woman in ten or one in twenty died in childbearing when conditions weren’t too awful.
North Carolina mountains didn’t fill up; they lived to be old there. Almost no childhood mortaility either.
My theory is with reliable food and enough space, people do pretty well.