Bacteria make major evolutionary shift in the lab
Det du nå skal lese er i følge kreasjonistene noe som er helt umulig, som aldri har skjedd og aldri kommer til å skje. Men la oss se bort fra dogmatisk idioti ideologi, og heller konsentrere oss om virkeligheten.
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.
For 20 år siden tok evolusjonsbiologen Richard Lenski en enkelt E-coli bakterie og grunnla 12 laboratorie-kulturer basert på bakteriens etterfølgere. Disse har nå gått gjennom mer enn 44.000 generasjoner og mutasjoner underveis har ført til hovedsakelig små evolusjonsmessge endringer - med ett unntak:
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.
Egenskapen kalles Cit+ og her kommer noe av det mest fascinerende (mine uthevinger):
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."