You might have fallen head over heels in love with your S.O. because of their brilliant blue eyes, their brain, or even their tattoos. You might have a “type.” You might not. Regardless, behavioral geneticists now believe that your sexuality is, at its core, the same as everyone else’s: defined by genetics.

A new paper published in Nature Human Behavior has the potential to upend what we previously thought attracted us to others. Postdoc Matthew Robinson worked under geneticist Peter Visscher at the University of Queensland in Brisbane in Australia to analyze 24,000 pairs of husbands and wives of European ancestry. They compiled information on people’s height and body mass index (BMI) and created a predictive model to figure out the height and BMI of their partner — a looming dude would probably be attracted to a statuesque woman (the study was done on husband-wife pairs). The researchers then compared a partner’s predictive height with their actual height.

What Robinson and his colleagues found was a surprisingly strong correlation between people’s heights. (There was a slightly weaker correlation between people’s own BMI and the BMI of their partners.) This means that people are unconsciously choosing partners with similar genes to themselves.

That goes against the theory of assortative mating that’s been promoted among social scientists like Gary Becker when explaining how people partner up. Popular theories include people being attracted to each other for their educational levels. The biological basis of partnering has been muddled — some have thought it has something to do with finding a genetic pool that is distinctly different from one’s own, pointing to the various genetic diseases that crop up (like Tay-Sachs) among groups that marry within restricted in-groups or among populations who marry their cousins or have gross hots for their own daughter. Others point to the fact that the reason why we are innately attracted to people who look like us — and, by extension, our parents — is because we’re seeking a feeling of trust and familiarity that’s important for bonding.

Robinson’s study isn’t the first to suggest that married couples seem to have genes in common; a study published last year in Nature Immunology found that couples developed look-alike immune systems the longer they stayed together.

That’s not to say that there’s nothing connecting the social constructs of assortative mating with the biological foundations. The group also studied 7780 British couples and found that there was — as Becker predicted years ago — an educational link between people who couple up. Researchers think this means that people aren’t necessarily choosing people purely based on how many graduate degrees they’ve tacked on after their name, but rather that those high achieving nerds are composed of a certain type of genes that make them attractive to others with that very genetic makeup.

Picking your S.O. isn’t just reflective of who you are and what you value in a relationship, in other words: It “affects the genomic architecture of traits in humans.” When tall people keep marrying each other, average human height goes up. When tall, intellectually rigorous people keep marrying each other, expect that sort of academic rigor to appear more heightened. Robinson and his team’s next steps include looking for how psychiatric traits — like neuroticism or schizophrenia — act as signals in partnering up.