“No man is an island, entire of itself,” wrote English poet John Donne. Nearly four centuries later science is gaining a fuller appreciation of just how literally true that is.

In addition to the bacteria that can make us sick, researchers have known for a few decades that we play host to friendly microbes as well. They help our body by performing important tasks such as breaking down food components to make them digestible or processing nutrients so we can make use of them. Although the womb is sterile, we start acquiring our microscopic guests the minute we are born.

The sheer number and broader influence of these bugs may surprise you. For starters, microbes outnumber your body cells by 10 to 1. (The bacteria are much smaller than human cells, so their total weight is often estimated to be around two to five pounds.) In effect, we are each a walking superorganism, hosting our own unique microcommunity. No two individuals share the same makeup of microbes and their genes, not even identical twins. Nobel Prize winner Joshua Lederberg dubbed this inner ecosystem a microbiome, acknowledging its complexity and interconnectedness.

More to the point, your health, your life span—and even some of your actions—may have more to do with the genetic variation in those microorganisms you host than they do with your own genes. Our cover story, “The Ultimate Social Network,” by Jennifer Ackerman, describes the efforts to map our human microbiome—no easy feat when certain critters, such as the gut bacteria that prosper in an oxygen-free environment, are challenging to grow in petri dishes in a laboratory. The results are illuminating. As you will learn, among other things, microorganism groups may influence not only how well we digest but also how much we eat. In addition, they have an important part in how well our immune system performs.

For a different kind of community effort—one involving teenagers and science that can benefit humankind—see the box at the left.

Award Winner
Look for the announcement of the winner of the Science in Action Award in June. Scientific American is sponsoring this $50,000 award, plus a year of mentoring, as part of the second annual Google Science Fair, a global online competition for students aged 13 to 18. The award will honor a project that addresses a social, environmental or health matter and could make a difference in the lives of a community or group. Find more information at www.google.com/sciencefair and at www.Scientific­American.­com/science-in-action.

This article was published in print as "We the People."