Identical twins don't share everything. The mix of viruses in a person's gut, a new study says, is unique to each of us, even if we share nearly all our DNA with another person. That is, at least according to our poop. This year scientists have been working to decode the genetics of the beneficial microbes that live inside us, like the bacteria that help us digest food. But those trillions of bacteria have partners of their own—beneficial viruses. Jeffrey Gordon and colleagues wanted to see what those viruses were like, and how they differed from person to person. To do it, they studied fecal samples that came from four sets of identical twins, as well as their mothers. Each identical twin had virus populations that didn't resemble those of their sibling—or anybody else, for that matter.
Remarkably, more than 80 percent of the viruses in the stool samples had ...
