Social Microbiomes

A study published in late-November of 2024 found that in addition to sharing all sorts of knowledge, cultural norms, and history, human beings share elements of their gut microbiomes with other people.

Our gut microbiomes consist of all sorts of bacteria, fungi, archaea, and viruses, some of which can cause or contribute to cardiovascular, respiratory, and neurological issues, while others help us resist harmful pathogens and allow us to digest food and metabolize medicines.

These ecosystems are dense with variety in most people, containing hundreds of species, but the vast majority of those species are bacteria, and most are from just a few dozen bacteria species.

There’s evidence that some treatments, especially antibiotics, can negatively impact out gut microbiomes, killing off some of the species we rely upon in addition to the ones we’re hoping to destroy. And there’s increasing suspicion that we might be able to target and possibly even address a number of chronic issues (especially those associated with digestion and inflammation) by tweaking our gut-flora so that this ecosystem is favorably (for us) rebalanced.

We know that what we eat and drink impacts our gut flora, and we know that our environments play a massive role in what our gut ecosystems look like—even more than our genes, according to some research.

Even knowing that, though, it’s not necessarily intuitive that hanging out with different sorts of people might play a role in our physical and mental health, as would seem to be the case based on that aforementioned 2024 study that used social network mapping and sequencing data from the microbiomes of 1,787 adults living in isolated villages in Honduras to map the relationship between these networks—who spends time with whom—and the gut composition of these subjects.

What they found was that even tangential, non-close relationships can result in the sharing of gut flora between people, but even more interesting is that these microbiota can be spread to secondary connections, as well. So if I share some of my gut flora with you, someone I’m close to, you might then share it with someone you know, but whom I’ve never met.

Thus, it’s not just our physical environments that matter in terms of determining the composition of our gut microbiomes, and as a result (to some degree at least), our physical and mental health; it’s also our social networks, spread out across those we know, those known by those we know, and possibly even those known by those known by those we know.

The nature of each relationship matters, of course, as do countless other variables. But this finding is useful in that it may help us think in broader terms when we’re considering the nature of our microbiomes and the variables that could be be shaping them (and as a result, shaping many aspects of our brains and bodies).