In the early 1900s, scientists discovered that each person belonged to one of four blood types. Now they have discovered a new way to classify humanity: by bacteria. Each human being is host to thousands of different species of microbes. Yet a group of scientists now report just three distinct ecosystems in the guts of people they have studied.
“It’s an important advance,” said Rob Knight, a biologist at the University of Colorado, who was not involved in the research. “It’s the first indication that human gut ecosystems may fall into distinct types.”