"Paternity can now be verified by a simple test – but that doesn’t mean it should be"

[Major Nikon]

13. Yes it does happen just like that sometimes

The reason words like cuckolding fall out of use is because people generally don't like to discuss infidelity, even though it is quite common. I've heard those who study evolutionary psychology say that marital infidelity is more or less equal between the sexes, but the reasons why are considerably different. Men are predisposed to disperse their genetic material as widely as possible while women are predisposed to seek out a mate based on his ability to provide, but will seek out a lover based on genetic superiority. So while both sexes have a primary interest in seeking out the success of their genetic line, the manner in which it manifests is different.

So while women may not have a conscious desire for this, at some level and at some rate it will happen just that way, just as men will father children outside their own primary relationship for reasons that are also evolutionary. The only reason it doesn't happen more often is because of the availability of effective birth control.