* 22:00 09 June 2008 by Bob Holmes
* For similar stories, visit the Evolution Topic Guide

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.

And because the species in question is a bacterium, scientists have been able to replay history to show how this evolutionary novelty grew from the accumulation of unpredictable, chance events.

Twenty years ago, evolutionary biologist Richard Lenski of Michigan State University in East Lansing, US, took a single Escherichia coli bacterium and used its descendants to found 12 laboratory populations.

The 12 have been growing ever since, gradually accumulating mutations and evolving for more than 44,000 generations, while Lenski watches what happens.
Profound change

Mostly, the patterns Lenski saw were similar in each separate population. All 12 evolved larger cells, for example, as well as faster growth rates on the glucose they were fed, and lower peak population densities.

But sometime around the 31,500th generation, something dramatic happened in just one of the populations - the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use.

Indeed, the inability to use citrate is one of the traits by which bacteriologists distinguish E. coli from other species. The citrate-using mutants increased in population size and diversity.

"It's the most profound change we have seen during the experiment. This was clearly something quite different for them, and it's outside what was normally considered the bounds of E. coli as a species, which makes it especially interesting," says Lenski.
Rare mutation?

By this time, Lenski calculated, enough bacterial cells had lived and died that all simple mutations must already have occurred several times over.

That meant the "citrate-plus" trait must have been something special - either it was a single mutation of an unusually improbable sort, a rare chromosome inversion, say, or else gaining the ability to use citrate required the accumulation of several mutations in sequence.

To find out which, Lenski turned to his freezer, where he had saved samples of each population every 500 generations. These allowed him to replay history from any starting point he chose, by reviving the bacteria and letting evolution "replay" again.

Would the same population evolve Cit+ again, he wondered, or would any of the 12 be equally likely to hit the jackpot?
Evidence of evolution

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.

In the meantime, the experiment stands as proof that evolution does not always lead to the best possible outcome. Instead, a chance event can sometimes open evolutionary doors for one population that remain forever closed to other populations with different histories.

Lenski's experiment is also yet another poke in the eye for anti-evolutionists, notes Jerry Coyne, an evolutionary biologist at the University of Chicago. "The thing I like most is it says you can get these complex traits evolving by a combination of unlikely events," he says. "That's just what creationists say can't happen."

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0803151105)

Wow, make sure FeralCat sees this!

lol like anything would make a difference in her mind. She has said as much herself.

Need I say it? 46 & 2 are just ahead of me...

Bump for Eljay or anyone who thinks he has a point.

I seriously have no idea how the ID movement came up with the "no new information" propaganda, but its false. Its not even a good way of looking at things. Evolution does not even need more information, just different . . . posing this kind of rebuttal shows a complete lack of understanding of genetics.

New info is added to the genome, but that is not what drives evolution, and it not how changes are made, some changes do include new data in the code, some dont, some swap, some move its not a good way of looking at it at all, its a sly way to take advantage of the folks who have never had proper education in genetics and evolution.

Correct me if I'm wrong about this - but Evolution presumes that all life has eminated from a single source