Can evolution be easily predictable? A new research with Escherichia coli bacteria suggests affirmative,
Scientists began the research with three different populations of E. coli. The bacteria in each population were naturally competing for 2 different types of foods: glucose and acetate.
After 1,200 generations, each population had divided into two categories, each focused physiologically to either glucose or acetate. After investigating the bacteria at 16 points over its evolution, the team discovered an important resemblance in the variations that had happened.
“In all three populations it seems to be more or less the same core set of genes that are causing the two phenotypes that we see… In a few cases, it’s even the exact same genetic change,” Matthew Herron (University of Montana) said. “There are about 4.5 million nucleotides in the E. coli genome. Finding in four cases that the exact same change had happened independently in different populations was intriguing.”
The team suggested that one specific form of selection, ‘negative frequency dependence’, played a significant role. As the population of one kind of specialized bacteria rises the amount of resources for them will reduce, giving bacteria who specialize in the different food a great advantage.
However, it is very important to note that Bacteria such as E. coli produce asexually. Therefore, these findings do not necessary explain how sexually-reproducing organisms might have evolve. In addition, The E. coli populations were also growing in a very constant and rather stable environment, which might have influenced any predictability.
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Photo credit: Rocky Mountain Laboratories, NIAID, NIH