Over time, random mutations enable organisms to adapt and diversify, often when geographically separated groups of the same species grow better suited to their local environment and less like members of the other group.

But that's not the only way that genetic diversity can arise. Researchers have reported cases of cichlid fishpalm trees and finches adapting to different ecological niches and splitting into different species despite living in the same place. In 2008, evolutionary biologist Michael Doebeli of the University of British Columbia (UBC) in Vancouver and colleagues reported that E. coli bacteria can also diversify while sharing a test tube.

In that study, they fed easy-to-digest glucose and a harder-to-stomach acetate to homogeneous populations of the bacteria, and let the bacteria chomp away. E. coli can switch between the two foods, but the team found that in each test tube two groups emerged, specialized in consuming either glucose or acetate. What they did not know was which genetic path each group took to achieve its specialization.