I got to thinking about the expanding view of self and how recent discoveries about the complex microbial ecosystems that dominate life on earth, have changed my view on life. Rather than an organism separated from the rest of the world, the human body is actually a superorganism that interacts with the microbial ecosystems in the environment around us through the trillions of bugs that make up our microbial “aura”.
Science has taught us that although our human genome changes slowly, the human microbiome – the entire collection of genes found in all of the microbes associated with the human host – can be altered fairly rapidly. Although there’s still a lot we don’t know about the complex relationship between bacteria, humans, and the rest of the environment, we do know that our microbiome is shaped not only by things such as diet and pharmacautical use, but also by microbes and genes (e.g., horizontal gene transfer) we encounter from the food we eat, water we drink, air we breathe, and humans we interact with.
Health is contagious in the sense that we’re influenced by the “health” of the microbial ecosystems that come in contact with our own microbiome. This is clearly evident in the case of infectious disease where we pick up a pathogen from another human or animal that makes us sick, but it also happens in less subtle ways.
It was long believed that the reason children who grow up with pets have decreased risk of developing autoimmune disease, is because the increased exposure to pathogens from their dogs and cats somehow trained their immune system. However. we now know that people pick up bacteria from the animal microbiome, and that these bugs probably increase the diversity and resillience of their own human microbiome (1).
We’re also learning that some diseases that have long been considered non-communicable, could be contagious in the sense that we share bacteria with other humans. dysbiosis is a key driver of chronic disease, and it can be hypothesized that close contact (e.g., kissing, shared household) with dysbiotic microbiota could have a negative impact our own microbiome.
Contagious health isn’t only of significance in contact with other living organisms, but also applies to our interactions with microbiota from the rest of the environment. E.g., when we’re exposed to the complex bacterial communities in healthy farm soil we pick up bacteria that potentially increase the diversity and health of our own microbiome (2).
It’ very hard to measure contagious health, and it’s still unclear to which extent contact with microbial ecosystems in the environment is able to alter the adult human microbiome.
Forensic identification has long focused on analysis of human DNA left behind on crime scenes, but recent studies suggest that we also leave traces of our microbial genome behind and that this DNA could potentially be traced back to the source.
When examining the microbes left behind on a keyboard, researchers found that they with a high percentage of accuracy could trace the bugs on the keys back to the right person (3). Just like with the skin microbiome, one study also suggests that it’s possible to identify someone by looking at microbes recovered from saliva (4).
Although it’s still unclear whether microbial DNA analysis is actually a viable approach in forensic science, it tells us a lot about the microbial fingerprints we leave behind us.
We’re a part of a global microbial ecosystem
The expanding view of the human body as a superorganism that is connected to the rest of the environment through a cloud of microbes, changes the perspective of life. One starts to think of life on earth as an organic cycle of water, soil, plants, animals, and humans all linked by complex microbial ecosystems. Humans perturb these ecosystems with chemicals spills and modern food production techniques, and the effects ripple through the global ecosystem and affect the health of both our human- and microbial self.
The human body as an ecosystem
I’ll finish this short post with a TED Talk by Brendan Bohannan, where he explains the idea of the human body as an ecosystem.