For decades, “opposites attract” has functioned as one of dating culture’s most repeated assumptions — the idea that a chaotic extrovert and a quiet introvert, or two people with clashing habits, somehow complete each other. The largest study ever conducted on the question says otherwise. Researchers analyzed 133 traits across roughly 80,000 couples and combined that with a meta-analysis spanning more than a century of prior research, and found that partners resemble each other — not complement each other — on the overwhelming majority of characteristics that make up a person.
The Numbers Behind the Myth
The 2023 study, led by geneticist Tanya Horwitz at the University of Colorado Boulder’s Institute for Behavioral Genetics and published in Nature Human Behaviour, is the most comprehensive test of the “opposites attract” idea to date. The team first reviewed 199 prior studies covering 22 traits in millions of male-female couples dating back to 1903, then ran an original analysis of 133 traits across roughly 80,000 opposite-sex pairs using the UK Biobank database. Across nearly all of it, the pattern held: for 82% to 89% of the traits studied, partners were significantly more similar to each other than two randomly paired people would be. Only about 3% of traits showed any tendency toward pairing with someone different, and that pattern turned up in just one narrow part of the analysis.
Some correlations were strong: political values scored a .58 correlation between partners on a scale where 1.0 would mean a perfect match, and traits like religious attitudes, education level, and substance use showed similarly high alignment. Others were weaker — the correlation for neuroticism, for instance, came in at just .11 — but even the weak correlations still leaned toward similarity rather than difference.
Attitudes Draw You In. Personality Keeps You There.
A separate, earlier line of research adds an important wrinkle: not all forms of similarity matter equally, and not all of them show up right away. A study of 291 newlywed couples from the Iowa Marital Assessment Project, published in the Journal of Personality and Social Psychology, found that couples showed strong similarity in attitudes and values by the time they married, but comparatively little above-chance similarity in personality traits like extraversion or conscientiousness at that same stage. What the researchers found more telling was what happened next: personality similarity, not attitude similarity, was the stronger predictor of marital satisfaction over time. Attitudes are easy to spot across a first date or two; personality takes sustained daily contact to fully reveal itself — and it’s personality alignment that seems to matter most once two people are actually living a life together.
Why “Like Attracts Like” Starts Almost Immediately
Research out of the University of Kansas suggests this similarity-seeking isn’t something that develops slowly inside a relationship — it starts almost instantly. In a series of studies led by psychologists Angela Bahns and Chris Crandall, published in the Journal of Personality and Social Psychology, researchers observed real pairs forming in public settings and tracked newly acquainted college students over time. They found that how similar two people are is “immediately and powerfully” shaping whether a connection forms — often within the first few minutes of interaction — and that partners and friends showed very little change in their personalities or values afterward. In other words, people aren’t drifting toward each other gradually so much as selecting for sameness from the very start, then staying that way.
Why This Myth Persists Anyway
If the data is this consistent, why does “opposites attract” still feel true to so many people? Part of the answer may be selective memory: a couple with one visible difference — one partner is a night owl, the other an early riser — is memorable precisely because it stands out against a backdrop of everything else they share. The traits people notice most in day-to-day life, like hobbies or energy level, are also a small slice of the full picture; the deeper alignment in things like values, intelligence measures, and substance use is less visible day to day but more determinative of who ends up together in the first place, according to the Nature Human Behaviour research.
What This Means If You’re Dating
None of this means couples need to be identical to work, and it doesn’t mean every difference is a problem. But the research is fairly unambiguous that similarity, not contrast, is the dominant pattern among real-world couples — and that the kind of similarity that predicts long-term satisfaction (personality and daily-life compatibility) may matter more than the kind that predicts initial attraction (shared attitudes and values). If a potential partner feels comfortably familiar rather than thrillingly different, the research suggests that’s not a red flag. It might just be how compatibility actually works.
