The Theory

Results of experiments on e. coli at Michigan State University have been published in the Proceedings of the National Academy of Sciences.

Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli

Zachary D. Blount, Christina Z. Borland, and Richard E. Lenski^*

Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824

Contributed by Richard E. Lenski, April 9, 2008 (received for review March 26, 2008)

The role of historical contingency in evolution has been much debated, but rarely tested. Twelve initially identical populations of Escherichia coli were founded in 1988 to investigate this issue. They have since evolved in a glucose-limited medium that also contains citrate, which E. coli cannot use as a carbon source under oxic conditions. No population evolved the capacity to exploit citrate for >30,000 generations, although each population tested billions of mutations. A citrate-using (Cit⁺) variant finally evolved in one population by 31,500 generations, causing an increase in population size and diversity. The long-delayed and unique evolution of this function might indicate the involvement of some extremely rare mutation. Alternately, it may involve an ordinary mutation, but one whose physical occurrence or phenotypic expression is contingent on prior mutations in that population. We tested these hypotheses in experiments that "replayed" evolution from different points in that population's history. We observed no Cit⁺ mutants among 8.4 x 10¹² ancestral cells, nor among 9 x 10¹² cells from 60 clones sampled in the first 15,000 generations. However, we observed a significantly greater tendency for later clones to evolve Cit⁺, indicating that some potentiating mutation arose by 20,000 generations. This potentiating change increased the mutation rate to Cit⁺ but did not cause generalized hypermutability. Thus, the evolution of this phenotype was contingent on the particular history of that population. More generally, we suggest that historical contingency is especially important when it facilitates the evolution of key innovations that are not easily evolved by gradual, cumulative selection.

In other words, specifically those of a blogger at conservapedia.

There are two claims made in the paper: that a strain of E. colii evolved the ability to utilize citrate, and that the strain first had a mutation which while it did not allow the utilization of citrate, in some fashion potentiated the later mutation. The first claim is supported by the optical density data in figure 1.

The second claim is demonstrated by repeat experiments using stored samples. In some cases, the ability to utilize citrate evolved, in some cases not. They report on the strains used, how often the ability evolved, etc. - divaricatum 11:30 June 20 2008 (PDT)

The argument on the talk page is not significant here. I only wanted to highlight this because it is totally going to cause a storm within the creation vs. evolution community. What this indicates is that life is capable of creating new abilities without having previously the genetic code.

Creationists believe mutation is real. Happens all the time. Some genetic code shuts down or begins to work. Here is a case where it seems creationists must face a possibility they've previously held fast can't be true. E. coli got something from nothing.

Wow. It's magic.

Of course the mystery is still there as to how it did it. The only thing the research team knew for sure is when a mutation sequence began that resulted in novel information, and they could make more of it do it again.

But it does not rule out God. It does offer a challenge to young earth creationism, sudden emergence, and the literal word of the Holy Bible.

Evolutionists of course love this for the threat it poses to intelligent design.

Bacteria make major evolutionary shift in the lab

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. (Am thinking creationists would wonder "what other pokes do you mean?" --ed.)

"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."

Of course I didn't get how serious this was until I read the words of NS writer Bob Holmes. So it isn't just novel information, it required a series of mutations to do it. That could be the model for why eyes evolved, or how scales became breasts or how eggs became wombs. Either it mutated over and over again because it wouldn't give up until it got what it wanted, or it was part of a sequence of planned steps to achieve more robust colonies through learning how to take what was once nothing of value and turn it into a source to metabolize.

Did I say wow. I really mean it now