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The body-politic

June 29, 2010

I just stumbled on a fantastic piece in Seed magazine from last year about the symbiosis between us and our microbes – one of the main points I’ve been trying to press home in my last few posts:

Through research that has blurred the boundary between medical and environmental microbiology, we’re beginning to understand that because the human body constitutes their environment, these microbial communities have been forced to adapt to changes in our diets, health, and lifestyle choices. Yet they, in turn, are also part of our environments, and our bodies have adapted to them. Our dinner guests, it seems, have shaped the very path of human evolution.

The piece is pretty short considering the amount of material it covers – there’s a lot to unpack:

The first thing most people think of is how this relates to disease, and not just the infections you can treat with antibiotics. There’s a lot of promising research looking at the effect of commensals on everything from obesity to mental illness:

Jeffrey Gordon’s lab at the Washington University School of Medicine in St. Louis showed that lean and obese mice have different proportions of microbes in their digestive systems. Bacteria in the plumper rodents, it seemed, were better able to extract energy from food, because when these bacteria were transferred into lean mice, the mice gained weight. The same is apparently true for humans: In December Gordon’s team published findings that lean and obese twins — whether identical or fraternal — harbor strikingly different bacterial communities. And these bacteria, they discovered, are not just helping to process food directly; they actually influence whether that energy is ultimately stored as fat in the body.

And we know almost nothing about how our increasing use of antibiotics could affect this balance. The FDA recently took tentative steps towards reducing the use of antibiotics in livestock, which are usually treated with antibiotics as a matter of course. The main concern there is the evolution of resistant strains and the spread of antibiotics into drinking water, but it’s also known that antibiotic-fed cattle gain more weight (which, in the case of livestock, is a good thing), but nothing is really known about how this affects the animals, or the humans that consume them, but it seems almost certain that disturbing microbial ecosystems will have an effect.

Another interesting concern is how we to make sense of all the new data we’re collecting. New gene-sequencing technologies allow us to probe more deeply into the diversity of microorganisms, but we barely know what we’re looking at:

While only a few major groups of the world’s bacteria live in the human body, within these groups are countless bacterial species that vary greatly from person to person. “The more people look at it, it seems like an endlessly diverse system[…]”

The recent metagenomic studies have revealed a daunting amount of diversity in microbial life, with none of the clear divisions we’re used to in the “macro” world. Among bacteria, the entire concept of species breaks down; it’s difficult for scientists to even categorize what they are seeing. Microbes offer a picture of life that is fluid and ever changing. To come to terms with this diversity, microbiologists are today relinquishing the desire to name names. When studying a community, they no longer focus on developing a roster of who is there; instead, they ask what kinds of genes are present and what their functions are.

Finally, there’s the idea of the “superorganism,” that comes from viewing ourselves not as completely human individuals, but as an ecosystem in which an untold multitude each participate in the whole.

It’s not just that our bodies serve as a habitat for other organisms; it’s also that we function with them as a collective. As the profound interrelationship between humans and microbes becomes more apparent, the distinction between host and hosted has become both less clear and less important — together we operate as a constantly evolving man-microbe kibbutz[…]

How do we make sense of this suddenly crowded self? David Relman suggests that how well you come to terms with symbiosis “depends on how comfortable you are with not being alone.” A body that is a habitat and a continuously evolving system is not something most of us consider; the sense of a singular, continuous self is a prerequisite for sanity, at least in Western psychology.

If you can see your own body as a community rather than an individual, how much further do you need to leap to see yourself as integrated into the larger, global community? I think that I consider this question more than most, but I still can’t get past my own individuality. This piece ends on what I think is an optimistic point, that this new science will challenge our image of ourselves, and allow us to think more collectively, but I’m not sure this is true.

In any case, it’s a fantastic read – check it out. And if you have any thoughts, let me know – I’d be interested to see what other people think about this.

[h/t Barney Holmes]


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