This is the most interesting paper I read in a while:
“Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli”
The Long Term Evolution Experiment has been growing 12 colonies of E. Coli in controlled conditions since 1988. At one point, after 30000 generations, one of the colonies evolved the ability to synthetize citrate in addition to glucose. Because the researchers had frozen samples from previous generations, they could restart the evolution process from an earlier point and see it happen again.
And no, I’m not doing biology here at Caltech. I would never wait 20 years for my experiments to finish!