Most of Your Cells Aren’t Yours

“All told, the [tiny] microbes in your body outnumber your own [much larger] cells by ten to one and can weigh as much as or more than your brain—about three pounds in an average adult. Each of us is thus both an organism and a densely populated ecosystem, with habitats harboring species as different from one another as the animals in a jungle and a desert.” Thus writes Stanford University microbiologist Nathan Wolfe in the 1/2013 issue of National Geographic. The more we find out about our bacteria, the more we might want to rethink who, biologically, we are.

Bacteria under a toenail. (

Bacteria under a toenail. (

The “habitats” that house these communities of bacteria and other microbes include our gums, guts,  genitals, underarms, inner elbows, tongue and throat, and the backs of our ears. Only a few species of bacteria make us sick. Others digest our food, make our vitamins, train our immune systems, moisturize and protect out skin. The bacteria that helps us digest milk crowd into the vaginal canal when a baby is passing through to help prepare it for breast milk.

There is an eerieness to me about all this. In many cultures people believe that their ancestors are always nearby, watching over them, helping or interfering with their lives. And devout Christians invoke deities, angels, and saints for assistance. So here for us secularists are our own ancient ancestors, the bacteria, every bit as with us and in us and influential as any holy spirit is thought to be.

What’s also eerie is that bacteria have a long history of becoming a part of other organisms, literally. Billions of years ago bacteria that could process light and excrete oxygen were absorbed into other cells and turned into the photosynthesizing chloroplasts of green plants. Other bacteria that boosted cellular energy were so useful to other cells that they became incorporated as the energizer mitochondria found in nearly all cells. In humans, bacteria don’t seem to have settled in as part of the furniture—yet—but they have been called “the forgotten organ.” Bacteria can be very good at making themselves indispensable.

We think of ourselves as a relatively new species, set off from the rest of nature by our brains. And indeed we are both new and different in some ways. But surely the way that bacteria have become integral parts of us, repeating a pattern billions of years old, reminds us what ancient creatures we really are.


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