“The bacteria species in your colon today are more or less the same ones you had when you were six months old. About 80 percent of a person’s gut microflora transmit from his or her mother during birth. “It’s a very stable system,” says Khoruts. “You can trace a person’s family tree by their flora.”

“The bacteria species in your colon today are more or less the same ones you had when you were six months old. About 80 percent of a person’s gut microflora transmit from his or her mother during birth. “It’s a very stable system,” says Khoruts. “You can trace a person’s family tree by their flora.”

— Mary Roach