The anxiety may turn out to be all too justified. One Cosmopolitan magazine poll showed that about half of its married female readers had had an affair. Since Cosmo readers tend to be young, this probably underestimates the likelihood that a woman will have an extramarital fling at some point during her life.

L. Wolfe, "The Sexual Profile of the Cosmopolitan Girl," Cosmopolitan, September 1980, pp. 254-65. See Metcalf and Humphries, eds., The Sexuality of Men, p. 116.

Worse still for husbands, research suggests that women are more likely to conceive when they commit adultery than when they have sex in their marriage bed.

See Robin Baker and Mark A. Bellis, Human Sperm Competition: Copulation, Masturbation and Infidelity, New York, Chapman & Hall, 1996.

DNA tests show that between 5 percent and 30 percent of babies born to American and British married women are sired by men other than their husbands.[146] Diamond, Why Is Sex Fun? p. 80.

In Germany, the figure is said to be approximately 10 percent. Since the law only allows the results to be used as evidence if the tests have been carried out with the woman’s consent, this is likely to be an underestimate., [147] Abendzeitung, 9.4.01, p. 5

Not for nothing is the identity of Jewish children always determined by way of their mothers. Not for nothing are attempts to change this rule meeting with determined opposition by from Orthodox rabbis. They fear, and with very good reason, that in case paternity tests are carried out the number of Jewish children will undergo a dramatic decline.

[148] Interview with Pnina Mizrachi, head nurse at Hadassah hospital in Jerusalem.

Why do women then have affairs when married?

This is because their husbands are almost, by definition not the best male there is. If he was, he would not have ended up with her in an agreement to seclude himself to her alone. A woman however

So the female wants to have her cake and eat it too.

Sex son theory: Peahens prefer beautiful males because they seek beauty to pass to their sons, who may in turn attract females. Males best at seduction are good at other things as well and a male with too many sexual opportunities will probably not give them all up for one. Looking at the bell curve, few are that much better than another.

There's also microchimerism, alpha widows and other baggage from Men that you have to deal with.

Penis size is another signal thought to indicate an evolutionary response to differing levels of female promiscuity - the larger the penis, the more efficient it is at scooping other men's sperm out of a woman's cervix (the glans - the head of the human penis - is specifically designed the way it is for this task alone). Africans and some South American natives have the largest penises; Asians the smallest. Europeans are in the middle. DNA analysis shows that around only 40% of all African males ever born have reproduced historically (while 80% of females have - twice as many); 60% of European males have reproduced (to 80% of European females); meanwhile, in Asia, it's been nearly 1-for-1 in terms of males reproducing to females.

Women seek monogamous marriage and do not seek sexual variety because their reproductive ability is limited not by how many males they mate with, but with how long it takes to bear offspring. An extra mating does not significantly increase the number of children she leaves behind. For men, casual sex presents a small risk but enormous reward.

Men who seize such opportunities leave more descendents than men who did not. Because we are descended from prolific ancestors, rather than barren ones, men are more likely to be tempted by casual sex than women.

Women are different. Having sex with a stranger might burden her with a pregnancy before she has won the man’s commitment to rear the child.

As a corollary to Roy F Baumeisters "Is there anything good about men":

Nowadays, couples coalesce around the twin undertakings of continuity (“I will ALWAYS be there for you”) and availability (“I will always BE there for you.”) Issues of exclusivity, uniqueness, and virginity have been relegated to the back-burner. It is no longer practical to demand of one’s spouse to have nothing to do with the opposite sex, not to spend the bulk of his or her time outside the marriage, not to take separate vacations, and, more generally, to be joined at the hip. Affairs, for instance – both emotional and sexual – are sad certainties in the life of every couple.

I know women hate to hear stuff like this and I’m sure are fuming as they read this post bc of the double standard our society has about male and female promiscuity but there are lots of double standards in this world. Some work in your favor and some don’t. Not every guy feels this way. Some guys wouldn’t hesitate to marry a woman who had a train ran on her by the entire Dallas Cowboy football team the day before he met her, other guys may not like a woman’s promiscuous past but can accept it and move on, and then there are guys who wouldn’t waste a nanosecond moving on if he knew a woman had slept around. To each his own. I’m just saying in general with all things being equal, most men prefer women with lower body counts. Guys generally don’t want the love of their life to be the gal the every Tom, Dick, Harry, Mike, John, David, George, Steven, James, Brandon, Bobby, Vincent, Joe, Don, Will, Bill, Aaron has had a piece of. Its a huge turnoff. She’s not your girl, it’s just your turn and stuff. Yes, it’s also an ingrained ego thing however a compromise is an open relationship maybe.

A psychologist on The Doctors claimed that 70% of people who cheat in marriages are women and they usually go back to guys who they were with when their partner count was closer to zero, most times the guy who took her virginity. That’s powerful info. Don’t marry a woman with a high N count unless attachment and sexual monogamy don’t mean anything to you.

You're in a gas station, you see guys taking swigs of milk from a carton then you're the chump who gets caught and has to pay for it. Perhaps the first users mishandled the milk and it's gone a little bad. But hey it's the only milk that's not skimmed near here. I mean I can handle it when it's not monogamous but not otherwise.