A study on romantic relationships found that for more than 80% of traits analysed – from political views to drug taking and the age at which people first had sex – partners were often remarkably similar.
Tanya Horwitz, a PhD student at the University of Colorado Boulder, US, and the first author of the study published in the journal Nature Human Behaviour, said: “Birds of a feather are indeed more likely to flock together.”
Couples were likely to share a similar birth year, and show similarities in terms of 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 weak and uncertain. This was seen in early risers pairing with night owls, left-handed people with right-handed, and those who have a tendency to worry with those who do not.
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Coupling along common 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.