Major evolutionary innovations launched right before the eyes of researchers. This is the first time evolution has been caught in the act of such rare and complex new features. And that view in question bacteria, scientists were able to replay history to show how this evolutionary novelty grew from the accumulation of unpredictable events a chance. Twenty years ago, evolutionary biologist
at the University of Michigan 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 over 44,000 generations Lenski and hours that is. Basically, the model Lenski saw were similar in each population. All 12 evolved more cells, for example, and rapid growth on glucose they were fed, and lower peak population density. But somewhere in the 31,500 th generation, the drama was one of the groups - the bacteria suddenly acquired the ability to absorb citrate, another nutrient in the culture medium that E. coli
usually can not use. Indeed, the inability to use citrate is one of the traits which bacteriologists distinguish E. coli
from other species. Citrate using mutants increased in number and diversity. "This is a profound change that we saw during the experiment. It was clearly very different for them, and that beyond what is commonly considered border
E. coli << As a species, which makes it particularly interesting, "says Lena. Rare mutations strattera 10mg? 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 had something special - whether it was a rare mutation in an incredible way, a rare appeal chromosome, say, or to be able to use citrate necessary accumulation of several mutations in the sequence. To find out which, Lenski turned to his freezer, where he delivered samples of each population every 500 generations. This allowed him to repeat the history of any starting point he chose to revive the bacteria and letting evolution "Retry" again. Will the same population evolve Cit + again, he wondered, or any of the 12 equally likely plucked jackpot? Replays showed that even when he looked at trillions of cells, only the original population re-evolved
Cit + - and only when he began playing with the generation of 20,000 or more. Something made it probably occurred about 20,000 generations, which laid the foundation for
Cit + later developed. Lenski and his colleagues are currently working to identify only that the change was before and how did it
Cit + mutation possible over 10,000 generations later. At the same time, the experiment stands as proof that. Instead, a random event can sometimes open evolutionary doors for one population that remain forever closed to other populations with different histories. Experiment Lena also another kick 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 developed through a combination of unlikely events," he says. "It's just what creationists say can not happen."
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