"Interestingly, there is no clinical or empirical evidence proving that two people will fare better in marriage if they are extremely smart. Nor is there evidence that a couple will do poorly in marriage if they are "not so bright." What does matter immensely is that the partners possess intellectual levels that are near the same. If one partner has a high intelligence quotient and the other partner's IQ is substantially lower, the couple are likely to be miserable together, regardless of how many other good traits they may have.
My own mom and dad fell victim to the disparity in intelligence levels. ... Amazingly, they remained married for seventy years! But for seventy years, they experienced the consequences of being mismatched intellectually. They seldom talked to each other beyond the obligatory "How was your day?" type of questions. They had difficulty discussing the important events of the day, or even the deeper tenets of the religious faith they shared. Although they loved each other and were irrevocably committed to each other, their conversations were limited to mundane, everyday things. This is fine if it's the level on which you and your partner want to communicate. But when you run much more deeply, and your partner is not able to go there with you, it can be a frustrating experience for both of you."
Neil C. Warren
founder of eHarmony