Check out who’s living in “your” body

| May 7, 2007 | 14 Replies

You are sitting there smugly thinking that you are in charge of your own body, and that you should be, because it is after all your body.  Well, you’re wrong.

The June 2007 Special Issue of Discover Magazine contains an article called “Your body is a planet.”  This article, written by Josie Glausiusz, recognizes that the average human body has 100 trillion cells. (Remember how much one trillion is?). I would have provided the link for this Discover article, but I did not see it anywhere at the Discover site.

Here’s the money question:  what percentage of those 100 trillion cells contain your DNA?  The answer is only 10%.  The other 90% of the cells in your body belong to “aliens”: bacteria, fungi and other microbes.

Most of the time we share our bodies harmoniously within 90 trillion or so microbes.  But sometimes the arrangement turns contentious, as when bloodsucking bedbugs, fleas and lives in beta, or when herpes simplex or human papillomaviruses cause surface membranes to erupt in nasty pustules or warts.

These “visitors” include athletes foot fungi, Streptococcus sanguis (that resides in dental plaque), vaginal flora, the chickenpox virus that lies dormant (for the most part) near our spinal cords and the one trillion bacteria that live in the average human’s skin.

It is commonly known that helpful bacteria live in the human gut.  Did you know, however, that the average human carries around 3.3 pounds of bacteria in the gut?

I also learned about demodex mites. They like to live in the follicles of eyelashes, where they eat, mate and breed.  They rarely leave the eyelashes “except perhaps for a sporadic nighttime walk around your face.”

If you find it interesting that you are actually a menagerie, you might enjoy reading Tom Wakeford’s book, Liaisons of Life, From Hornworts to Hippos, How the Unassuming Microbe Has Driven Evolution (2001).

In his introduction, Wakeford writes that Pasteur was the person who renamed bacteria “germs.”  Pasteur became increasingly shrill as his fame increased. He “advised that these enemies of the people should be tracked down and destroyed.” (Page 7).  In truth, bacteria are more likely our friends.

A randomly chosen bacterium is far more likely to be digesting your domestic sewage or supplying oxygen for you to breathe than it is to be making you ill.  The vast majority of bacteria live harmlessly and unobtrusively on the surface of our seas and in our gardens, quietly undertaking biological processes crucial to every ecosystem.  Many species are essential to the production and digestion of almost all of the kinds of food that we eat, the recycling of our waste, and the fertility of our soils.

Wakeford’s book is about symbiosis, “the term used to describe long-term intimate associations between different organisms, usually involving microbes.”  (Page 14).  There are incredibly large numbers of types of symbiotic relationships.  For instance, lichens (the “crusty green and gray covering of rocks and tree trunks”) constitute a liaison between a fungus and an alga.  “These lowly lifeforms cover 10 times as much of the Earth’s surface as tropical rain forests.”

Consider also, fungi.  More than 90% of plants have domesticated their own species of fungus. Plants could not survive without their fungi, which form great networks underneath the soil.  Mushrooms are “merely a spore-dispersing device for its real body underneath the soils surface, a huge cotton wool mass of branching tubes hyphae that can spread for hundreds of feet in every direction.”  One mammoth fungus found in Montana had tentacles that covered 15 hectares of forest, weighed 100 metric tons and was more than 1000 years old.

Entomologists have found that microbial symbionts are found in the guts of virtually every insect.  Up to one half of the weight of a termite consists of wood-eating microbes.  They are passed to the next generation when young termites eat the poop of adult termites. (Page 91).

Darwin also wrote on the phenomenon of symbiosis:

We cannot fathom the marvelous complexity of an organic being; but on the hypothesis here advanced this complexity is much increased.  Each living creature must be looked at as a microcosm-a little universe, formed from a host of self propagating organisms, and conceivably minute and as numerous as the stars in heaven.”  (Page 130).

The varieties of symbiosis cause us to see the path from exploitation to mutual benefits as a fuzzy continuum.  Wakeford go so far as to suggest that we consider renaming many organisms: “Is a cow and animal or a microbial fermentation vessel when without the microbes, the cow would not exist?”

The same thing goes for that complex adaptive system most of us call “my body.”  The microbes we carry around seem to be using our bodies quite successfully, so much so that one might rightfully characterize human beings as microbial fermentation vessels.

However one characterizes the human body, it is clear that it is not nearly so simple as it is usually depicted.  The rampant symbioses characteristic of human bodies is nothing out of the ordinary in the scheme of nature.

Perhaps, before reading this information about symbiosis, you thought of your body as homogeneously your own.  But once again, real science prevails over folk science.  Don’t be so cavalier next time you are tempted to utter the phrase “I am.”  Perhaps “we” is a more appropriate first person singular.  And perhaps the soul will be the next time-tested concept to fall if science continues to push back the horizons of human ignorance.


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Category: Evolution, Science

About the Author ()

Erich Vieth is an attorney focusing on consumer law litigation and appellate practice. He is also a working musician and a writer, having founded Dangerous Intersection in 2006. Erich and his wife, Anne Jay, live in the Shaw Neighborhood of St. Louis, Missouri, where they are raising their two extraordinary daughters.

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Sites That Link to this Post

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  1. Ben says:

    I would like your expert opinion of this website…

  2. Erika Price says:

    Likening the human body to its own complex planet reminds me of the Gaia Hypothesis, which holds that we can look at the entire planet Earth as a large organsim. In both cases, we have an extremely complex and self-regulating system comprised of a wide variety of living things that all serve valuable, interdependent purposes. Every lowly cog in the system serves some kind of function, and has a like "foil" in the form of another organism (like the dance between animals and plants in producing oxygen and carbon dioxide).

    And then the Earth itself belongs to a great "organism" comprised of all the different planets, stars, and other assorted space particles. And so on. And so on. To think of it in such a way paints a beautiful and humbling picture, where nothing qualifies as "good" or "bad", "important" or "unimportant", "gross" or "gorgeous"; everything just exists, and coexists, and plays a part in a whole greater than itself.

  3. Dan Klarmann says:

    That low-salt hypothesis in Ben's linked page is amusing. I defy anyone who eats any packaged foods (incl. fast food, frozen low-salt dinners, etc) to get as little salt in their diet as did anyone in pre-industrial societies.

    Also, the western diet includes several times as much salt as the Chinese prefer.

    The US RDA is 2.4 grams for healthy adults. The average American consumption is 4 to 5 grams a day.

    The example of the rise in Lyme disease is specious. People are "getting" more obscure diseases now because ten times as many people survive from birth to middle age as did in any time before the advent of modern sanitation and then 20th century antibiotics.

    Also, it is not so much that people are getting more diseases, it is that more can be detected. Lyme disease is such a new discovery, and its late stage detection such a cutting edge procedure, that many people are discovering that their odd symptoms (formerly just called "rheumatism", "depression", etc) for the last 30 years are from this disease.

    This said, the web site is essentially proposing that Lyme disease can be cured simply by taking very high doses of salt and vitamin C (dozens of times the RDA for one, and hundred for the other). The salt has to be pure (no iodine or flow agents that are dangerous in high doses) and the "C" should be a particular brand name. Can you say "shill"?

    They might be on to something, but no actual studies have been done on the matter. Proceed with caution, and a doctor's supervision.

  4. Mary says:

    Erich – This post reminds me of the ancestor one you did a couple of days ago. Now then, who are all of those bacteria and other micro-organisms living within us related to in our long distant past? The same things we are, right?

  5. Erich Vieth says:

    Mary – Yes! I'm a big bag of little cousins!

  6. Nardy Henigan says:

    I am trying to make sense of the numbers. Ten trillion cells are mine, and the other 90 trillion cells are bacteria, fungi and other microbes. I'm assuming the overwhelming majority of these "aliens" are living in my gut, yet that's only 3.3 pounds. Let me estimate altogether the "aliens" equal 2% of my weight. So each of my cells is about 40-50 times bigger (by weight) than one of these "aliens" (on average — the mite is 1000s of times bigger than a virus). Anyway, does that seem like a reasonable (ball-park) estimate for the relative sizes of my cells and the alien cells?

  7. Dan Klarmann says:

    Some of "my" cells are a meter long, and many are on the order of inches. Muscle and neural cells are quite big. Bacteria (on the other hand) are very sophisticated, highly evolved, and optimized (evolved) to be as small as they can be and still fully function. Their DNA has a much smaller proportion of ghost genes and other inactive stretches than does mammal DNA. It also only has to code for one kind of cell (unlike our multicellular genes).

    Don't forget to count the phages living on the bacteria living in the mites living in your hair follicles. Or all the fungus cells that (in proper balance) aid in digestion and growth.

  8. Ed says:

    I applaud you for discussing this fascinating topic. Humans really don't like to think about such stuff, much less talk about it.

    I would just remind everyone that even our own body itself is a colony of cooperating cells that have a symbiotic relationship with an alien entity possessing it own DNA: the Mitochondria. We wouldn't be animated without it. I'll leave it to the reader to Wiki for more on this fact.

    BTW, commenter Ben wondered about the lack of sodium consumption causing Lyme disease. I'm VERY skeptical of that possibility for one big reason: the ratio of sodium to other elements in your body fluids is actively regulated to maintain a narrow range of relative concentration of these ions — a process called homeostasis — or you will quickly die. If you eat more sodium, your homeostatic machinery will do whatever it must to maintain the proper concentration, or you will die. If you don't eat enough sodium (or potassium or magnesium, etc.) your machinery will adjust the concentrations of the other ions to compensate. Active maintenance of this homeostasis is practically THE definition of Life.

    Bottom line, the sodium concentration in your blood is always pretty much the same, or you would very quickly cease to function.

    PS: Human (primate) Demodex is not as innocuous as you imply. Mutant variants abound which make life almost unbearable to the host and, because of ignorance, are often misdiagnosed as Delusional Parasitosis, Morgellons, Scabies. Some folks even believe they have been afflicted by Chem Trails. But they simply have Mange.

    Demodex SUX! They are not symbiots; they are parasites! We don't need them AT ALL!

  9. lala land says:

    that is kool!!!!!!! i never ever knew this!

  10. Erich Vieth says:

    Here is a link to some of this information provided by Discover Magazine:

  11. Erich Vieth says:

    Ebonmuse has recently written of those multitudes in our body:

    Consider this mind-boggling statistic: in the body of every healthy human being, there are ten times as many bacterial cells as there are human cells. If this seems impossible, realize that bacteria are prokaryotes, lacking the complex internal structure and therefore much smaller than our own eukaryotic cells. Most of the bacteria in the human body live in the intestines, and the 15 trillion or so bacteria in a healthy gut would just about fill a ten-ounce soup can.

  12. Erich Vieth says:

    The numerous organisms that we depend upon that live inside of our bodies are in danger, and so are we, according to this article in Scientific American:

    The human body has some 10 trillion human cells—but 10 times that number of microbial cells. So what happens when such an important part of our bodies goes missing?

    With rapid changes in sanitation, medicine and lifestyle in the past century, some of these indigenous species are facing decline, displacement and possibly even extinction. In many of the world's larger ecosystems, scientists can predict what might happen when one of the central species is lost, but in the human microbial environment—which is still largely uncharacterized—most of these rapid changes are not yet understood. "This is the next frontier and has real significance for human health, public health and medicine," says Betsy Foxman, a professor of epidemiology at the University of Michigan (U.M.) School of Public Health in Ann Arbor. Meanwhile, each new generation in developed countries comes into the world with fewer of these native populations . . .

    An overexuberance for the hygiene hypothesis, however, may be leading people astray, Blaser notes. "It's my hypothesis that the microbes that are present in dirt are irrelevant to humans," he says. "What are relevant are the microbes that we've had for hundreds of thousands of years—[and] are disappearing."

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