Evolution illustrated first-hand (Science)

GeoffP

GeoffP

Caput gerat lupinum
Valued Senior Member
The "evolution-have-you-seen-it-where-is-it-can't-be-proven" debate is over.

Guess who won.

Bacteria make major evolutionary shift in the lab

22:00 09 June 2008

NewScientist.com news service

Bob Holmes

Richard Lenski, Michigan State University
Jerry Coyne, University of Chicago

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)

http://www.newscientist.com/channel...make-major-evolutionary-shift-in-the-lab.html
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Debate?

Geoff
 
This certainly disproves the notion that a new trait cannot come out of nowhere - score one for mainstream evolutionary thought v. quacks! However, what did this change involve to do that?

Also, it is notable that this is not dramatic change and it did take 3 billion years to go from single celled organisms to multicell organisms.
 
I remember a few years back about the discovery of bacteria that had evolved after living 50 years in the waste water of a nylon factor, to metabolize nylon! A novel ability with no need every exist before (as nylon as man made an ever existed before). The anti-evolution people still denied it, because the genes for metabolizing nylon were on a plasmid the calm divine plasmid infection or something. There is no winning with those people they will deny it to the point of claiming god is making it look like evolution is happening to test the faithful, no evidence what so ever can get around that argument.
 
John99 said:
They are still BACTERIA. Doesn't that mean anything?
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How significant would the evolutionary change have to be in order to be meaningful? Would the organism in question have to just "jump" there, or would there be incremental changes along the way?
 
Randwolf said:
How significant would the evolutionary change have to be in order to be meaningful? Would the organism in question have to just "jump" there, or would there be incremental changes along the way?
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Well i did say that "they" are still bacteria.
 
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So are you trying to teach me about the pervasiveness of life? I already know that. There are multitudes of changes bacteria can go through, weather by natural means or artificially induced.
 
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OilIsMastery said:
Yes. See John 99's comments. They are still bactertia. They didn't evolve into anything other than bacteria.
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Evolution is driven by such small changes. And, when another such occurs, they will be further still from their ancestral line. The accumulation of such changes in metazoans leads us to speciation.
 
john said:
So are you trying to teach me about the pervasiveness of life? I already know that. There are multitudes of changes bacteria can go through, weather by natural means or artificially induced.
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Some of those changes are evolutionary - potentially permanent, functionally significant, inherited changes, available for and established by selection on the overall population.

Simply labeling such changed organisms as "still bacteria" says absolutely nothing. You might as well dismiss the evolution of penguins from albatrosses as "still birds", or the evolution of birds from dinosaurs as "still vertebrates".
 
Hmm, a pity that no one wants to discuss the paper itself. In any case, one hardly studies evolution to debunk it, but rather to improve the theory of evolution. Also it is not the goal of the study to debunk creationistic beliefs, it does so in the passing, so to say.
 
Prince_James said:
This certainly disproves the notion that a new trait cannot come out of nowhere - score one for mainstream evolutionary thought v. quacks! However, what did this change involve to do
that?

Also, it is notable that this is not dramatic change and it did take 3 billion years to go from single celled organisms to multicell organisms.
Click to expand...

It did not come out of nowhere. It came from the existing E.coli, and the fact
that they fed it (with glucose?).

the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use
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Yes, they adapt. What does it prove? I don't like to eat cabbage, but if that
is the only food I can eat, I think my stomach will get used to eat it anyway.

I have a question though. Our food resources are from living things (vegetable
from plantation or meat from animal). What about the first living thing? What
do they eat?

Ok, don't bother, I was just kidding. I know most plantation eat carbondioxide
and water to produce carbohydrate for us. ;)
 
I don't like to eat cabbage, but if that
is the only food I can eat, I think my stomach will get used to eat it anyway.
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No. You can already digest cabbage, so that's no good.

A better example would be wood chips. Or perhaps, earlier in our evolution, lactose.


I still think the move to this forum is weird. Sam, in fact, was the first to mention 'miracles'.
 
CharonZ said:
Hmm, a pity that no one wants to discuss the paper itself. In any case, one hardly studies evolution to debunk it, but rather to improve the theory of evolution. Also it is not the goal of the study to debunk creationistic beliefs, it does so in the passing, so to say.
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True, generally. But at the same time, the "haven't seen evolution in our lifetime" argument is of old date and does in fact deserve specific falsification.

I hesitate to say "debunking", necessarily. Unless I already did. In which case I do not hesitate to say debunking.

Thankyou, my fellow Americans.
 
sniffy said:
Haven't evolutionary changes been observed in mosquitos as well? In our lifetime!!
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Licking carpet? let's not go there.

Anyway what about the question above. I can't find the original reference but have any of you come across one? Answer noobs!
 
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