H/t to who I don’t remember, we see an ancient concept of reproduction- long thought to be evil superstition– may in fact be true.
Telegony is the idea that offspring can have the physical characteristics of males a female has previously mated with, although they are not actually the fathers. People seem to have noticed this way back, because people noticed things in the old days, before it was a thoughtcrime, and because in small communities people would have known the woman, the first lover, and the husband/father, and been able to compare and see the influence on the children.
Genesis mentions the male and female becoming “one flesh”. Paul talks about how you don’t want to become one flesh with a prostitute. Until recently men have wanted to marry virgins, and non-virgins have been considered “damaged goods”.
Of course being sophisticated moderns we know this is all very silly. If a woman has intercourse and semen is expelled into her vagina, nothing at all happens, as long as no venereal disease is transmitted and no pregnancy occurs. Since most common venereal diseases are treatable, and pregnancy is easily prevented or ended, there is no reason for women not to have all the intercourse they want.
Until recently among certain subcultures, young people were tolerated or tacitly permitted all kinds of sexual gratification, short of intercourse. More recently among some that seems to include anal sex, which is probably not a good idea for anybody. But it seems that keeping the female reproductive tract clear of all sperm other than the one father of eventual children is the only way to assure 100% paternity, the basis of patriarchy and strong family life.