A Census of the Sisterhood

It pleased me to read the news yesterday concerning findings of the Human Microbiome Project, an organization of the National Institutes of Health. HMP has now taken a census of micro-organisms that share our bodies. We are host to some 100 trillion bacteria, ten for every one of our cells; it isn’t that we “host” them, exactly, although we do. Without them we would have major problems digesting our food. Long ago I had a poetic reaction to studying biology and imagined that each living being is a “chemical civilization.” Even back then (the 1970s) students came to value the crucial role played by our Symbiont Sisters; the scientific work to estimate their total number and subdivisions into “ethnicities” had not yet been done. Now it has. Ten thousand species live in us; all told they have 22,000 different genes—over against our own 8,000; they represent about 1 to 3 percent of our body mass—thus a person weighing 150 pounds will have 3 pounds of helpful guests—using a 2 percent figure. Biome, incidentally, comes from “living" and “mass.”

These civilizations are similar to our own—but only to mean what fractal mathematics calls “self-similarity.” That concept means that some arbitrarily selected whole will be approximately similar to a part of itself—while also being part of a greater whole also self-similar to itself.

Back in the 1970s it was mitochondria in cells that brought home, for me, the notion of a community of living beings, cooperating to form greater wholes. Mitochondria produce the cells’ energy; they are power plants in what looked to me then like cities—if greatly enlarged. Mitochondria have their own DNA; presumably they were, at one time, immigrants to cells, valued for their superior technology.

The more we think about bodies—which we imagine to be exclusively our own—and the more they look like vast aggregations of other living beings—who in turn carry within them what seem to be alien symbionts—and so on until (as in my case), I imagined invisibly tiny “little people” who use enzymes as their tractors, forklifts, helicopters, hoists—the more curious the picture becomes and the more strange we seem to ourselves. Are we these structures, by whatever name we call them: bodies, machines, communities, or chemical civilizations? I’m convinced that we are not. We can live our lives and never even think about such matters. But at some point understanding such mysteries matters. HMP, mindful of the public’s narrow interest in utility, points to advances in medical knowledge as the justification for this research. But for me, this too, like everything else, points at something beyond.