Replays showed that even when he looked ...

Major evolutionary innovations launched right before the eyes of researchers. This is the first time of evolution has been caught in the act of making such a rare and complex new features. And because the species in question bacteria, scientists were able to beat the story to show how this evolutionary novelty grew from the accumulation of unpredictable events a chance. Twenty years ago, an evolutionary biologist

at Michigan State University in East Lansing, USA, took one

bacterium Escherichia coli and used it for posterity found 12 laboratory populations. 12 of them growing ever since, gradually accumulating mutations and evolving for more than 44 000 generations, Lenski watches what happens. In general, the model Lenski saw were similar in each population. All 12 evolved larger cells, for example, as well as rapid growth on glucose they were fed, and lower peak population densities. But somewhere in the 31,500 th generation, the drama took place in one of the groups - the bacteria suddenly acquired the ability to absorb citrate, a second nutrient in the culture medium that E. coli

usually can not use . Indeed, the inability to use order strattera citrate is one of the features which distinguish the bacteriologists

Escherichia coli from other species. Citrate using mutants increased in number and diversity. "This is the most profound change that we saw during the experiment. This was clearly something quite different for them, and it is beyond what is generally considered the boundaries

E. coli << As a species, which makes it especially interesting, "says Lenski. Rare mutations? By this time, Lenski calculated enough bacterial cells had lived and died that all simple mutations must already happened several times. This meant that the "citrate-plus" feature was something special - or was it a mutation of an unusually improbable sort, rare use of the chromosome, say, or be able to use citrate must accumulate several mutations in the sequence. To find out which, Lenski turned to my freezer, where he had saved samples of each population every 500 generations. This allowed him to repeat the story with any starting point, he chose to revive the bacteria and allowing the evolution of the "Repeat" button again. Will the same people to develop Cit + again, he wondered, or any of the 12 equally likely to hit the jackpot? Replays showed that even when he looked at trillions of cells, only the original population re-evolved

Cit + - and only then, when he started playing from the generation of 20,000 or more. Something, he concluded, must have been about 20,000 generations, which laid the foundation for

Cit + evolve later. Lenski and his colleagues are currently working to identify just what it was before the change, and how did it

Cit + mutation possible more than 10,000 generations later. At the same time, the experiment serves as proof that. Instead, a random event can sometimes open the door for the evolution of one population that remain forever closed to other populations with different histories. Lenski's experiment is also yet another poke in the eye of anti-evolutionists, notes, an evolutionary biologist at the University of Chicago. "What I like most, he says, you can get these complex traits evolving by a combination of unlikely events," he says. "This is exactly what creationists say can not happen." Journal

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