Love Goes Through the Microbiome

When we fall in love, the microorganisms that colonise our bodies play a decisive role. The reason for this lies in evolutionary history.

Whether it’s love at first sight or an acquaintanceship that deepens over time - at the beginning of every relationship there’s that one point where it "clicks" between two people. The fact that this happens is due to our evolutionary history and is not just to do with obvious reasons such as visual attractiveness or common interests. Rather, nature has arranged that our choice of partner is also influenced by our microbiome, i.e. the entirety of the microorganisms that live on and in us.

The more different, the better

"Choosing a partner is not just about beauty, but about volatile substances, the body’s own odours, and these are produced by the microbiome. And the more the other person is differently populated here compared to ourselves, the more attractive we find that person," explains Gabriele Berg, head of the Institute of Environmental Biotechnology at Graz University of Technology (TU Graz). Evolution has had a hand in this because the immune system has had to constantly adapt over the course of time and still has to do so in order to prepare itself against new pathogens and environmental influences. Offspring with the most diverse immune systems possible have the best chance of such an adaptation.

"From an evolutionary perspective, it therefore makes sense to reproduce with someone who has a completely different immune system to yourself," says Berg. As the composition of the microbiome is strongly driven by the immune system, the circle that began with the microbiome-related choice of partner is then completed in the offspring.

We are slowing down nature ourselves

Incidentally, the fact that this natural mechanism of falling in love doesn’t always work is down to us humans ourselves. We are all too happy to cover up our own fragrances with perfumes or deodorants, and changes in hormone levels caused by medication, such as contraceptive pills, also influence the body’s own "magnetism". "There are many studies that show this. Of course, it has to be said that other factors also play a role in the end."

The influence of other factors affects the long-term prospects of a relationship even more. Just because nature brings two people together who could produce offspring with the most diverse immune system possible, does not mean that they will participate in a long and happy love affair. "Evolution is so selfish in this case that it only brings people together because of the good reproductive prospects, even if these people may not have so many interests in common. For a long-term partnership, some would probably prefer to look for different partners," says Gabriele Berg.