Richard Lenski (top) and Jeffrey Barrick view bacteria cultures in Lenski's lab.: They have watched the bacteria's DNA evolve over 40,000 generations.Courtesy Michigan State University / photo by G.L. Kohuth

Sometimes you’ll hear people cast doubts on evolution because no one has ever seen it happen. As if that’s some sort of great insight. No one has eve “seen” atomic fusion, either, but the fact that the Sun was shining this morning is pretty strong evidence that, yep, it happens. No one has ever “seen” gravity. Seen gravity’s effects, sure. But seen gravity itself? Like Ms. Ono once asked, Who Has Seen The Wind?

Evolution used to be in the same boat. The effects of evolution are visible everywhere, in every cell of every living thing on the planet. But seeing the actual process of evolution? That was another matter.

Until now. Scientists at Michigan State University (go Spartans!) have been growing bacteria in bottles for the past 21 years. Every so often, they would freeze a sample for later study. Well, “later” is now. DNA sequencing and computer analysis have advanced to the state where they can readily map the genome of each sample. And guess what? The bugs evolved exactly as evolution says they should. Mutations in the genome pop up at random intervals. Mutations that help the bug survive—like make more efficient use of food, or fend off disease—get passed on to future generations, and eventually spread through the entire colony.

Twenty-one years may not seem like enough time for a species to change. But, as Mia Sorvino said in the truly awful 1997 movie Mimic, think generations, not time. In the two decades of study, the little bacteria went through 40 thousand generations—the equivalent of roughly 800,000 years in human terms. Plenty of opportunity for evolution to do it’s thang.

And the experiment continues. Understanding mutations in bacteria might help us understand the mutations that lead to some forms of cancer. In recent generations, the rate of mutation has increased; the scientists would like to know why.

Richard Lenski, the scientist heading up the research, has put together a video explaining his work.