[Mz]

That's a ridiculous assumption, on so many levels.

A woman can get raped and end up pregnant. She can have zero interest in sex and still reproduce.

"Evolution" favors those who survive long enough to reproduce. Merely being born is not sufficient. If you have 20 kids and none of them live to adulthood, your genes die out. There is a correlation (that seems to run two ways) between having fewer kids and having them survive. Cultures with high child mortality also have high birth rates. So fucking like rabbits does not by itself ensure survival.

Generally speaking, the human race places a high value on a faithful woman. A woman who is faithful is more likely to get support from the father of her children, thus her children are more likely to thrive. Most likely, "bastard" is a swear word or insult because, historically, having a child out of wedlock tended to doom both mother and child to extreme poverty.

Etc.