It's true because science just told us. Some bored British academics recently determined that fellows of higher intelligence "are more likely to value monogamy and sexual exclusivity than less intelligent men." Or are they just better at not getting caught?
Who knows! Presumably, the smart guys are also better at not answering silly survey questions about whether or not they are stepping out on their women. (Or men, I suppose. It is the '90s!) The other thing smart dudes are better at than dumb dudes? Ha, no, other than "Everything." They are also better at being godless liberals. The study found that atheism and lefty politics are more common in smart people.
In an unrelated study, science has also just confirmed that the Pope does indeed shit in the woods.