I'm thinking not reading ai chat. When girls are born there is much less distance between vagina opening and cervix etc and pathogens, could easily enter the cervix area and cause damage, which would render the woman unable to reproduce. Babies shit all over their genitals and kids are generally grabbing and poking their junk all the time. An inner barrier not easily disturbed would protect the much shorter birth canal. Pathogens probably eliminated a ton of women from reproducing without the mutation for the hymen. Ergo only hymenated women maintained reproductive capacity over the years.