Rob Knight's research on the bacterial communities growing on and inside the human body almost makes human beings seem like little more than scaffolds for bacteria. Knight and his collaborators were among the first to look at the nature and consequences of these bacterial communities, finding, for example, unique features in the gut microbes of obese mice. As gene sequencing has become cheaper and faster, he has gone on to develop a map of bacteria all over the human body. Our faces, for example, are covered with a kind of skin bacteria called Propionibacteria, but not our ears, which are just enough cooler to make them uncomfortable.

He's now found shifts in gut microbes in obese people, and discovered that for the individuals in his study, the bacterial community on one hand was different from the other—two subjects shared only 18 percent of their species. How can that be possible when we rub our hands together all the time? The news continues to roll in: Changing the microbes in the gut can change how much a mouse wants to eat, and the microbiomes of humans who have sharply restricted their intake of calories differ substantially from those on normal diets. For more information...