Inside you, with you, within you, and on you live hundreds of different species. Your own body is a giant, poorly understood, complex ecosystem.  Though we think of ourselves as single individuals of a singular species, we are far more. Many of the organisms inside us could not live without us, nor we without them. Like much life on earth, we are made up of many organisms, as has been the case probably from the beginning of multi-cellular life. 

         The ecosystem that is your body is too complex to quickly explain. Here are brief descriptions of a few environments within you:

Small Bowel and Colon

         Most people know that bacteria thrive within our lower gut.  Few know how many thrive there. 

         In the colon, there are more than one trillion bacteria per cubic centimeter.  They are necessary to digestion.  Besides keeping us alive by helping us ingest nutrients, they constantly war and fight, allying with and destroying each other with breathtaking efficiency.

         We change our gut flora whenever we travel, take in different foods or drinking water.  Changing our bacterial population changes what we digest, ingest, and produce.  This shifting bacterial world inside us modifies our foods and what carcinogens and toxins we destroy.  Our trillions of lower gut bacteria interact with our immune system in innumerable unknown ways that are critical in preventing a host of different diseases.

Skin

         Studying only six people, a recent NYU study demonstrated an average of fifty different species of skin bacteria for each. A total of 180 species was found, with relatively little overlap from person to person.  Hundreds of different viruses also reside all over your skin.  They literally change with the wind.  The ecosystem of your skin changes every time you shake a hand or caress a loved one.

Central Nervous System

         Ever get a canker sore? The herpes simplex virus erupting in your mouth has probably lived in your central nervous system since infancy.  The herpes zoster causing your grandmother’s shingles has domiciled in her spinal cord for seventy or eighty years.  Recent evidence in mice found that resident herpes viruses helped fight off bubonic plague and other virulent diseases.   Many other viruses live throughout your nervous system, prodding immunity and infiltrating your DNA.

Human Genome

         It is now estimated that 8% of human DNA comes from various retroviruses.  The most famous retrovirus species is the AIDS virus.  This stunning facts means that many different retroviruses have been exchanging genetic material with our ancestors probably well before humanity existed.  As you read this sentence these resident retroviruses continue to change your internal DNA code.

The Cell

         You may have read recent studies of human origin that looked at mitochondrial DNA, the separate genetic material of the energy powerhouses of cells.  Professor Lynn Margulis and others theorize that mitochondria were originally separate organisms. Perhaps billions of years ago, they were captured and then controlled, by other cells.  Those other cells eventually evolved to produce human beings.  Multi-cellular life on Earth may have begun when one species overcame and incorporated another.

The Real Human Ecology

         Our very cells were probably once separate organisms.  Our bodies are filled with the DNA of viruses that might destroy us.  Our internal environment is itself the product of thousands of different species that come and go, changing our internal environment in countless ways.

         You are an individual filled with hundreds of different organisms.  Your own body is a giant ecosystem with hundreds of species coming and going, changing the information and energy flux of your life. Understanding the multi-species system of your body is just one more enormous project for systems biology. Understanding how we live and die with so many other species inside and around us will help us recognize how our immune system operates, while defining the causes and cures for dozens of separate diseases. Our own personal ecosystem is vast.  Yet is extremely small, just a tiny part of the far vaster planet on which we live.

         We cannot exist without the other.  Understanding our place in that system will be critical to our survival.

Dr. Matthew Edlund, M.D., M.O.H., director of The Center for Circadian Medicine, is an expert on applied public health, sleep medicine and psychiatry. A former professor at Brown and University of Texas medical schools, he can be reached via email to DocME@DoctorEdlund.com. And CLICK HERE to subscribe to our new Fitcast, via the iTunes Store.