Now that may have all changed.
A major evolutionary innovation has unfurled right in front of researchers' eyes. It's the first time evolution has been caught in the act of making such a rare and complex new trait.
Essentially, they took E. Coli and grew it in twelve different populations for 44,000 generations and found that some of them obtained characteristics absent in E. Coli. The kicker is that the were able to test when the traits originated and reproduce the results.
The replays showed that even when he looked at trillions of cells, only the original population re-evolved Cit+ – and only when he started the replay from generation 20,000 or greater. Something, he concluded, must have happened around generation 20,000 that laid the groundwork for Cit+ to later evolve.
Lenski and his colleagues are now working to identify just what that earlier change was, and how it made the Cit+ mutation possible more than 10,000 generations later.