Attraction between two people isn't limited to appearances or cultural affinities. Recent work shows it can also be rooted in a more intimate dimension: mental health. The idea that psychological disorders could bring individuals together may be surprising. However, an international study reveals that this phenomenon transcends cultures and spans generations.
Researchers focused on how couples share certain psychiatric disorders. Beyond social similarities or personal preferences, the study reveals a marked tendency: many partners receive similar diagnoses. Data collected in three countries provides solid evidence to better understand this mechanism, known as "assortative mating."
An unprecedented global study
The analysis focused on more than six million couples from Taiwan, Denmark, and Sweden. The geographical and historical diversity of the data allowed for the examination of trends from the 1930s to the present day. Nine psychiatric disorders were studied, including schizophrenia, depression, bipolar disorder, anxiety, autism, ADHD, addictions, and OCD.
The results show that, for each of these disorders, spouses are more likely to share the same diagnosis than would be expected by chance. This correlation is observed in all the cultures analyzed, with only a few differences between countries. For example, OCD or bipolar disorder are found to be associated less frequently in Taiwanese couples than in Nordic countries.
These similarities persist from one generation to the next, suggesting a stable phenomenon for nearly a century. The statistical strength of the results indicates that this is not a simple coincidence, but a deep and lasting trend.
Mechanisms that remain mysterious
Researchers propose several hypotheses to explain this resemblance. Social constraints could limit the choice of partners for people suffering from psychiatric disorders, thereby increasing the likelihood of meeting someone with a similar experience. Prolonged cohabitation can also encourage the onset of disorders in the spouse, creating a psychological closeness over time. Finally, sharing the same difficulties could strengthen mutual understanding, making the emotional alliance more stable and stronger.
These explanations are not mutually exclusive and could even combine. The phenomenon appears sufficiently consistent to suggest it is based on several intertwined factors. Researchers emphasize the universal nature of the results, observed independently of cultural differences or healthcare systems. This consistency suggests that common mechanisms, still poorly identified, play a determining role.
An impact on future generations
The study highlights significant consequences for offspring. Psychiatric disorders often have a heritable genetic component. When both parents share the same pathology, the risks for their children increase considerably. The probability is then more than twice as high compared to a situation where only one parent is affected. The diseases particularly involved are schizophrenia, bipolar disorder, addiction, and depression.
The children of these couples therefore represent a particularly vulnerable group, requiring increased attention in terms of prevention and monitoring. The authors suggest that doctors should systematically take into account the mental health of both parents, and not just the initial patient. These results provide valuable insight for better understanding family transmissions and refining public health strategies.
To go further: what is assortative mating?
Assortative mating is a phenomenon observed in many animal species, including humans, where individuals tend to choose partners who resemble them in certain traits. These similarities can be physical—such as height, build, or eye color—but also behavioral or cultural, like education level, beliefs, or even dietary preferences.
This bias in partner choice does not necessarily result from a conscious decision: it often stems from biological or social mechanisms that favor the recognition of familiar characteristics, attraction to signals perceived as compatible, or the geographical and cultural proximity that increases the chances of meeting similar individuals.
This type of selection plays an important role in the evolution of populations. By reinforcing the transmission of certain common traits from one generation to the next, it contributes to shaping the genetic and cultural diversity of a species. In humans, it can influence the distribution of characteristics within a population—for example by accentuating differences in height or education level between couples—and have indirect effects on health or adaptation.
Assortative mating thus illustrates how our partner choices are not random, but reflect complex dynamics between biology, environment, and society.
Article author: Cédric DEPOND