> lot of first time mothers are rather mediocre

I had a hen who was sitting on a clutch of eggs this summer. Did everything right: kept them warm, turned them regularly, etc.

Then one hatched and she promptly lost interest in the rest, leaving them to die.

It used to be that people had between six and twelve children, so all children grew up among babies learning this crucial knowledge from their parents and younger siblings. They'd end up having children within a few years of moving out, too, so there was no forgetting about it, either.

In addition, a lot of first time mothers died, as did their babies.

I once read an account of an octogenarian woman in a nursing home. A new doctor was assigned to her. Looking over the medical records, she'd had chronic urinary infections her entire adult life, until her husband passed away. She had urinary incontinence her entire adult life. They never had any children, though not for lack of trying.

Turns out that her husband had been penetrating her urethra throughout their marriage. When the old woman was questioned about these medical issues by the doctors, she told him that though it had hurt the first time, she expected it to and never thought much of it. Nor had she connected the onset of incontinence and infections with the act.

So no, I don't think that this is necessarily true, either.

Story of my life.