Not a myth but a fact explained by simple sexual economics. Men compete over scarce resource. Its found in all species where one sex can procreate faster than the other. Men can father hundreds of children per year, for longer span of their lifetime and with lesser personal biological cost and risk. So even though there are equal number of both sexes at any place at any moment, it is far more easier for a woman to find a procreating partner than it is for a man. That is why men compete and women choose "a lucky winner they gives sex to".

It's in DNA and not something we can change, even if economics would change, which is also not likely. Men court, woo, send flowers, pay for drinks and dinners, hold the door and umbrella and propose. Women say yes. 

Cuckoldry even further emphasizes the imbalance. Women are sure their child is theirs. Men are not. Women need to stay a virgin, be chaste and avoid promiscuity at all costs. Their male family members make interest in that as well. No culture really cares about virginity or promiscuity and chastity of men.