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 [1]?). I would have provided the link for this Discover article, but I did not see it anywhere at the Discover [2] 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. [3] 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 [4] (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 [5], “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 [6] (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 [7] will be the next time-tested concept to fall if science continues to push back the horizons of human ignorance.
Print this post [8]
[9]