Evolution seen on a laboratory bench

13 April 2008


In an experiment that might help to silence the critics of evolution, scientists in California have made genes evolve on a laboratory bench.

Writing in this week's PLoS Biology, Brian Paegel and Gerald Joyce from the Scripps Research Institute used a DNA relative called RNA to show how beneficial genetic mutations can build up over time to make biological systems progressively more efficient.  This is the central tenet of Darwin's theory of natural selection, or survival of the fittest as it is also known, but critics often claim that there is no direct evidence for how it might take place.

Michael Faraday in his lab, by Harriet MooreThe two researchers created their "evolution machine" by mixing together an enzyme called RNA Ligase, which can link pieces of genetic material together, some genetic material and two other enzymes that could make copies of the results.  In this set up the RNA Ligase joins up the genetic material to assemble a structure called a promoter, which then activates the enzymes that copy the RNA Ligase.

In this way, the better the RNA Ligase is at assembling the promoter, the more it will be copied and so its population will grow.  But in the wild organisms compete for resources, so to recreate this situation, whenever the RNA Ligase reached a set threshold number of copies of itself the researchers reset the process using just a small sample of the RNA Ligase that had been produced and adding fresh reagents.  But every time they did this they reduced the supply of the genetic material needed to form the promoter, making it increasingly more difficult for the RNA Ligase to trigger its own reproduction.

The whole process was automated, controlled by a computer and carried out on a microfluidic chip resembling a small plate ten centimetres or so in diameter.  The team started the system evolving by adding a variety of mutated RNA Ligase enzymes and then letting it proceed at its own pace.  After 70 hours and 500 cycles like this the resulting RNA Ligase enzyme had evolved to become 90 times quicker at copying itself by picking up 11 genetic changes along the way. 

The team hope that their simplified approach to demonstrating evolution could even make it into the classroom so that biology students can experience the process for themselves. "This is evolution at the level of molecules as a fact, not a theory," says Joyce.  "This is what it looks like when a computer controls conditions that push molecules to adapt in order to thrive - survival of the fittest on the smallest scale possible."


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