There's an adage that in romantic relationships, opposites attract. Now, a large, new study confirms that just like many old sayings, it's wrong.
In an analysis of about 200 studies involving millions of couples, researchers came to the conclusion that there is little behind the claim that opposites attract. If anything, the one about birds of feather flocking together is much closer to the truth.
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When it came to the hundreds of "traits" the study analyzed — from political leanings to smoking and drinking habits — partners were almost always more alike than different.
It was only in relation to 3% of traits that people tended to pair off with someone who had different inclinations, according to the findings published recently in the journal Nature Human Behaviour.
To be fair to the adage, the findings do not mean that people rarely find themselves attracted to someone who is much different from them.
"We looked at cohabiting and co-parenting couples," explained lead researcher Tanya Horwitz, a doctoral candidate at the University of Colorado Boulder. "So, this study speaks to long-term relationships."
On average, the findings show, long-term partners are similar in a host of ways — from religious and political beliefs, to educational background and certain aspects of intelligence, to lifestyle habits.
The results are based on data from 199 published studies involving millions of male-female couples, dating as far back as 1903. The researchers also did their own analysis of data from the UK Biobank, an ongoing research project that is collecting health and genetic information from about 500,000 British adults.
In all, the researchers looked at over 150 "traits," assessing how often couples were in step on each. And for 82% to 89% of those traits, partners were clearly more likely to be similar than different.
Among the traits where couples were most strongly aligned were political and religious beliefs, education level, certain IQ measurements, and smoking and drinking habits.
Then there were personality traits — where, Horwitz said, there's been less certainty as to whether opposites attract or repel.
Overall, the study found, partners did tend to be more alike than different on the "big 5" personality traits (extroversion, openness, agreeableness, conscientiousness and neuroticism). But the correlations were not as strong as those for factors like political or religious attitudes.
Extroverts, for example, were only slightly more likely to pair up with a fellow extrovert rather than an introvert, Horwitz said. The finding was similar when it came to neuroticism.
There were only a few traits where, in the UK Biobank study, partners were somewhat more likely to be opposites than in lockstep. One was "chronotype" — that is, night owls more often paired with early risers than fellow night owls.
Horwitz had no ready explanation for that, and said it's possible it was a chance finding.
Where did the notion that opposites attract originate? Horwitz noted that research in the 1950s, by psychologist Robert Winch, suggested that some traits are "complementary." So a person might choose a mate who has "opposing" qualities that complement some of his or her own.
But there has been little scientific data to back up the idea that opposites attract.
"It's basically folk wisdom," said Angela Bahns, an associate professor of psychology at Wellesley College in Massachusetts.
Bahns, who was not involved in the new research, has studied the topic. In a 2016 study, she found that in both romantic pairings and friendships, people are typically drawn to like-minded individuals. And there was no evidence that partners or friends changed over time to become more in sync; the similarities were there from the get-go.
Part of the story is "structural," Bahns explained. If you're a college graduate, for instance, you're more likely to be around a lot of college graduates, versus someone with only a high school diploma.
But there's also the fact that similarities can be very attractive: It's "validating," Bahns said, when someone shares your beliefs.
Interestingly, Bahns has found that in a bigger, more diverse environment -- a large university, versus small college, for example — people tend to be even more similar to their romantic partners and friends.
Bahns said that may be because when you have a large pool of potential mates and friends, you can — however consciously or unconsciously — be more selective.
No one, though, is saying that people cannot have close relationships just because they are dissimilar in some ways.
"This does not mean that people can't be, or shouldn't be, attracted to someone different from them," Horwitz said. "We're talking about what's observed in relationships, on average."
This study did not include same-sex couples, who've been the subject of much less research. If data on those couples had been included, Horwitz noted, any findings specific to them might have gotten lost in the ocean of data on heterosexual partners.
Instead, the researchers are doing a separate analysis focusing on same-sex pairs.