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Hitch yourself to another human being for long enough, and eventually you’ll notice yourself starting to change in subtle and not-so-subtle ways. Maybe you’ll take on some of their weird habits, or find yourself watching the same TV shows or buying the same brand of toilet paper they like. Maybe you’ll attach new meaning to certain words or phrases that only the two of you understand. Maybe you’ll start to look alike.

But not all changes take so long to make themselves known. According to a study recently published in the journal Developmental Psychology, there’s a biggie that happens in the first year or so of marriage — not in what you do or what you buy or how you look, but in who you are.

The study authors recruited 169 heterosexual newlywed couples at three different points in time: six months into marriage, around their first anniversary, and six months after that. At each point, participants filled out surveys designed to measure their levels of what’s known as the Big Five personality traits: extraversion, agreeableness (which encompasses traits like kindness and affection), openness to experience (which is linked to insight and imagination), neuroticism, and conscientiousness. In the span between the first survey and the last one, there were a handful of personality changes that kept popping up — and that spanned across all the other different factors the researchers measured, like age, demographics, relationship length and living status before marriage, and relationship satisfaction.

“We tend to think about personality as a pretty static variable,” says lead study author Justin Lavner, an assistant professor of psychology at the University of Georgia. But “what this study did is show that even very early in marriage and over a relatively short period of time, people’s personalities do change.” (A big caveat: This study was done on straight newlyweds, and Lavner was reluctant to extrapolate any of its findings to same-sex married couples.) Here’s what they found.

Both men and women become less agreeable.

To be frank, this one is kind of a bummer — marriage, it seems, immediately turns people meaner and more curmudgeonly. Lavner, though, has a theory that puts a slightly more positive spin on the finding: Marriage is hard, and so is adjusting to it. “They’re coming to terms with their new status, and that can involve new arrangements in terms of living, and financial, emotional, and physical interdependence at a level that may not have been the case before,” he says. “It also may be, to some degree, a sense that actual marriage is not the same as their ideal marriage.” Coming down from the newlywed high and landing in real life would make anyone cranky.

Women become less open and men become less extroverted.

Another two changes that seems like a strike against the whole marriage thing — get hitched, immediately fall into a rut — but Lavner believes these are actually kind of warm and fuzzy. “It may be that there’s more focus on the relationship and less on other levels of social involvement,” he says. How to feel about these shifts, in other words, may depend on your perspective: What looks to a friend like a slight withdrawal from social life may, to a spouse, look more like a renewed commitment to spending time together. In the words of the great Liz Lemon, yes to staying in more.

Women become less neurotic and men become more conscientious.

First, let’s clarify what “neurotic” means here, which is a little different from the way the word is commonly used: In the context of the Big Five, it refers to a tendency toward negative affect, or how likely a person is to become anxious, sad, or any other unhappy emotion. Past research suggests that women, on average, tend to score higher in neuroticism than men.

They also tend to be more conscientious — and both of those findings, Lavner explains, may come into play here, with people taking on more of the positive qualities of their partner. The change in men “may reflect the fact that their wives are encouraging them to be a little more conscientious, and reinforcing that,” he says, while the change in women may be the same rubbing-off effect in reverse.

Overall, it’s kind of a mixed bag — the very beginning stage of a marriage can change people for the worse, but also for the better. A better takeaway, then, might be the fact that they change at all. “Oftentimes, when people talk about being unhappy in their relationship, they talk about, ‘Oh, I changed,’ or ‘He changed, she changed,’” Lavner says. “But that can work in both directions, like, ‘Maybe things weren’t as good, and then one of us changed in some way and that really made things better.’”