Humans are physically designed for moderate levels of cheating. Not monogamy like gorillas (small penises, big strong males), but not a sexual free-for-all like bonobos (large penises, males same size as females). Studies of different societies and cultures around the world, and historical studies where possible, show a pretty consistent level of children who are not biologically fathered by the husband. I believe the figure is about 10%. This seems to suggest that it is not very culturally determined.
I think that it is generally believed that in prehistorical tribes, couples would be together for a few years, and produce generally one child, then change partners.
Taboos on infidelity, which we have, reflect that fact that infidelity, like many sexual practices, is most effective (as a means of reproducing), when we do it ourselves, yet are able to prevent others from doing so. It really is biologically driven human nature to want to cheat, yet to want other people not to.
Our superior intelligence does not override our biological drives, it just allows us to understand them better, and if we want to, channel them in other directions.