A new study by Mikhila Humbad and colleagues at Michigan State tested whether spouses converged in their basic personality over a long marriage.
This is not really so surprising, though. Our basic personality characteristics are one of the most stable parts of us. We may come to look and sound more like our spouses as we come to imitate one another's facial expressions and speech. But personality mostly stays put.
What this study really shows, I think, is that people with enduring marriages were similar in values, and complementary in personality, to begin with. The researchers note that they do not have many recently married couples in their study - not surprising, since they were piggybacking on the long-running Minnesota Twin Study to find their couples.
I would expect that couples with dissimilar values and non-complementary personalities would be less likely to make lasting marriages.
But neither the couples in the real study, nor the couples in the hypothetical study, would be likely to show much personality change.