Even the ten percent is probably a myth. Misattributed paternity is mostly quoted at a level somewhere between one and four percent.
I even think it was an item on "science or fiction" at the SGU , not sure though

That said , i largely agree with the sentiment expressed in the monogamy bit.

Long term monogamy is clearly a social construct. I think all the evidence shows that if that social construct did not exist, monogamy (in the true sense - one partner, no cheating) would be even more rare than it already is. That does not make monogamy a bad thing - I'm sure stealing would be a lot more common if there was no law against it - but we have to put it in perspective.

And I must end with the following gem:
Dr. Gregory House: Thirty percent of all Dads out there don't realize they're raising someone else's kid.
Dr. Eric Foreman: From what I've read, false paternity is more like ten percent.
Dr. Gregory House: That's what our Mom's would like us to believe.

I've had a number of conversations recently about fidelity, monogamy, polyamory, sex outside of marriage due to various events in my life.

In a way, I'm fascinated by polyamory because I don't know how it can work long term. Eventually, it seems to me, an uneveness will develop in the relationships that engenders hard feelings and things fall apart.

I think that is distinct, however, with your friends' issue with long term physical fidelity. It seems to me that sexual health and interest in variety can (and probably should) take numerous forms. The permutations alone could keep someone up at night (wink-wink-nudge-nudge say no more). Anyway, again, the challenge is the emotional content. I could see a long term monogamous relationship with few bounds on physical sexuality outside the relationship, being healthy. As long as the primary relationship has a strong emotional foundation.

Of course, talking from a quarter century of monogamy and (I think) fidelity, it is much easier to conceive of extramarital physical activities without risk to the primary relationship.

I'm done blabbering. Thank you for your patience.