Confirmed: Opposites don’t attract

Birds of a feather are indeed more likely to flock together, study indicates.


Positive correlations between partners can affect estimates from genetically informed study designs and enhance trait variation and prevalence. Scientists are aware that formal meta-analysis has yet to look at human partner correlations across several categories of attributes. However, previous studies of similarity between human mating partners have mostly revealed evidence of positive correlations.

Hence, scientists from CU Boulder conducted systematic reviews and random-effects meta-analyses of human male–female partner correlations. Contrary to popular belief, opposites don’t attract each other.

That is the main finding of a thorough investigation examining more than 130 traits and millions of couples over a century. It was discovered that partners were more likely to share 82% to 89% of the attributes examined, including political inclinations, age of first sex, and substance use behaviors.

Individuals tended to partner with others who differed from them for only 3% of qualities and only in one area of their examination.

The study has significant ramifications for the genetic research field and offers insight into invisible forces that might influence human interactions.

Senior author and IBG Director Matt Keller said, “A lot of models in genetics assume that human mating is random. This study shows this assumption is probably wrong. That what is known as “assortative mating”—when individuals with similar traits couple up—can skew findings of genetic studies.”

The writers of the new publication reviewed prior studies or performed a meta-analysis, as well as their original data analysis.

In 199 studies that included millions of male-female co-parents, engaged, married, or cohabiting pairs, they examined 22 features for the meta-analysis. The earliest research was done in 1903.

Additionally, they examined 133 features among roughly 80,000 opposite-sex pairs in the United Kingdom using a dataset known as the UK Biobank, including many that are infrequently examined.

Couples of the same sex were excluded from the study. The authors are investigating those individually because the patterns there could differ dramatically.

Both studies revealed strong associations for characteristics including political and religious beliefs, educational attainment, and specific IQ tests. For instance, the correlation for political views was on a scale where 0 indicates no association and one indicates that couples always share the feature.58. 

Traits related to substance abuse also exhibited strong relationships, with heavy smokers, heavy drinkers, and abstainers being attracted to people who shared their habits.

However, the connections between factors like height and weight, illnesses, and personality traits were much smaller but still positive. For instance, neurotocism correlated of.11.

There was significantly no correlation for several qualities, such as extroversion.

Horwitz said, “People have all these theories that extroverts like introverts or extroverts like other extroverts, but the fact of the matter is that it’s about like flipping a coin: Extroverts are similarly likely to end up with extroverts as with introverts.”

The researchers concluded from the meta-analysis that “no compelling evidence” exists for any feature that opposites attract. They did discover a few, albeit few, features in the UK Biobank sample that appeared to have a negative connection.

A person’s chronotype (whether they are a “morning lark” or “night owl”), worry propensity and hearing impairment were among them. Further studies are required.

Unsurprisingly, birth year was characteristic for which couples were most likely to have similarities.

However, even little-studied characteristics, such as a person’s history of sexual partners or whether they were nursed as children, revealed some link.

Horwitz said, “These findings suggest that even in situations where we feel like we have a choice about our relationships, there may be mechanisms behind the scenes of which we aren’t fully aware.”

According to the authors, couples have traits in common for various reasons: Some people have similar upbringings. Some people are drawn to those who are like them. Some become increasingly alike as they spend more time together.

There can be aftereffects depending on the reason.

For instance, according to Horwitz, if short individuals are more likely to have children with other short people and tall people with other tall people, there may be an increase in the proportion of persons at the extremes of height in the coming generations. The same is true of psychological, physical, or other characteristics.

There can be societal repercussions as well. For instance, a few tiny earlier studies have revealed that Americans are becoming increasingly inclined to marry someone with a similar educational background—a development that some have theorized may expand the social gap.

Notably, the current study also demonstrated that connections between attributes varied in strength between populations. They anticipate that they will change over time as well.

The researchers caution that the correlations they found were fairly modest and should not be overstated or misused to promote an agenda (Horwitz points out that assortative mating research was, tragically, co-opted by the eugenics movement).

Scientists noted, “We’re hoping people can use this data to do their analyses and learn more about how and why people end up in the relationships they do.”

Journal Reference:

  1. Horwitz, T.B., Balbona, J.V., Paulich, K.N. et al. Evidence of correlations between human partners based on systematic reviews and meta-analyses of 22 traits and UK Biobank analysis of 133 traits. Nat Hum Behav (2023). DOI: 10.1038/s41562-023-01672-z
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