The power of animal magnetism has brought numerous couples together, but when it comes to who we fall for, scientists believe there’s little truth in the adage that opposites attract. A study on romantic relationships found that for over 80 percent of traits analyzed, from drug taking to political views, partners were typically remarkably similar.
Tanya Horowtiz, the first author of the study published in the journal Nature Human Behaviour and a PH.D. student at the University of Colorado Boulder, said, “Birds of a feather are indeed more likely to flock together.” According to the research, between 82 and 89 percent of traits examined were similar among partners, with only three percent ranking as substantially different.
For the study, scientists reviewed previous research on how similar or dissimilar couples tended to be, work that covered 22 traits across nearly 200 papers involving millions of male-female partnerships dating back to 1903. Then, the group followed up with a fresh analysis of 133 traits in nearly 80,000 opposite-sex couples enrolled in the UK Biobank project. Because behavior may differ for same-sex couples, scientists investigate these relationships separately. In both pieces of work, couples largely matched across a range of traits, including religious and political views, levels of education and some measures of IQ.
Heavy drinkers, smokers, and teetotallers all tended to partner with people who shared their habits. However, couples didn’t match on every front. Weight, height, medical issues and personality traits all varied among couples. For example, extroverts were no more likely to partner up with other extroverts than introverts. Horwitz said, “The fact of the matter is that it’s like flipping a coin.” Couples were likely to share a similar birth year and show similarities in less well-studied traits, such as how many sexual partners they had had and whether they were breastfed as a baby.
When opposites did appear to attract, the associations were often uncertain and weak. This was seen in early risers pairing with night owls, left-handed people with right-handed people and those who tend to worry with those who don’t. Horwitz said, “Even in situations where we feel like we have a choice about our relationships, there may be mechanisms happening behind the scenes of which we aren’t fully aware.” The work builds on previous studies that suggest romantic partners often share core beliefs, hobbies, and values, as may be expected.
Relationships based on common ground can arise when people grow up in the same area, socialize with a narrow group of friends, or grow more similar the longer they spend together. Coupling along standard lines could have future consequences, the researchers note. For example, if taller people pair up with other taller people and shorter people with other shorter people, the coming generations could have more individuals at the extremes of the population’s height distribution. The same applies to social habits and other traits.
Some studies suggest that people increasingly pair up along educational backgrounds, raising concerns of a widening socioeconomic divide.