Opposites are supposed to be the icing on the cake – this is true in romcoms, but in real life it’s completely different. A new study asked numerous characteristics of couples. It was about political attitudes, drug consumption and also the question of at what age they had sex for the first time. “Soft” factors such as views were queried, but also “hard” factors.

The result: The couples agreed with each other on more than 80 percent of the factors. “Our results show that birds with the same feathers are more likely to fly together,” said Tanya Horwitz of the University of Colorado Boulder. For this study, published in the journal Nature, the researchers re-evaluated previous results, in addition to conducting a new analysis of 133 traits on almost 80,000 couples who took part in the UK Biobank project. In total, over 130 characteristics from millions of heterosexual couples over a period of over 100 years were included. The study is based on a very large number of people, so it is not a form of “homework study” for which a few dozen people were surveyed.

The new sample from the UK Biobank is the most detailed. There are hardly any characteristics with a negative correlation, so opposites do not attract.

Some characteristics correlate very strongly, including political and religious views and level of education. Smokers, drinkers and teetotalers also like to keep to themselves. Other factors such as height, weight, medical problems and personality traits can vary quite a bit

“Even in situations where we feel like we have a choice in our relationships, there may be mechanisms at work behind the scenes that we are not fully aware of,” Horwitz said. The finding has far-reaching consequences. “Many models in genetics assume that human mating occurs by chance. This study shows that this assumption is probably wrong,” said co-author Matt Keller. Partnerships are the central element in the transmission of genes, if the partner is selected selectively, completely different patterns emerge than assumed.

Relationships arise because of similarities. The circle of friends is already a special group and does not cover the entirety of society. People grow up in a certain environment and in this group they are subject to the same sociological influences. This shapes self-perception and worldview. Long partnerships also lead to further alignment. And some people are explicitly attracted to people who are similar to them.

The “social bubble” tends to reinforce and reproduce itself. In the USA, for example, it is well known that the social elevator through marriage has practically come to a standstill; today people commit themselves to a partner with a comparable education and a similar economic background. One of the consequences: the poor stay among themselves, the elite form “power couples”.

What: Nature Human Behavior