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Evolution In A Test Tube: Scientists Make Molecules That Evolve And Compete, 
Mimicking Behavior Of Darwin's Finches

Researchers have set up an artificial ecosystem inside a test tube where 
molecules evolve to exploit distinct ecological niches. (Credit: iStockphoto)

ScienceDaily (Apr. 30, 2009) — A group of scientists at The Scripps Research 
Institute has set up the microscopic equivalent of the Galapagos Islands—an 
artificial ecosystem inside a test tube where molecules evolve to exploit 
distinct ecological niches, similar to the finches that Charles Darwin famously 
described in "The Origin of Species" 150 years ago.

As described in an article published in the journal Proceedings of the National 
Academy of Sciences (PNAS), the work demonstrates some of the classic 
principles of evolution. For instance, research shows that when different 
species directly compete for the same finite resource, only the fittest will 

The work also demonstrates how, when given a variety of resources, the 
different species will evolve to become increasingly specialized, each filling 
different niches within their common ecosystem.

Conducted by Sarah Voytek, Ph.D., a recent graduate of the Scripps Research 
Kellogg School of Science and Technology, the work is intended to advance 
understanding of Darwinian evolution. Using molecules rather than living 
species offers a robust way to do this because it allows the forces of 
evolution to work over the course of mere days, with a trillion molecules in a 
test tube replicating every few minutes.

"We can study things very quickly," says Scripps Research Professor Gerald 
Joyce, M.D., Ph.D., who was Voytek's advisor and her coauthor on the paper. 
Joyce is the dean of the faculty at Scripps Research, where he is also a 
professor in the Department of Molecular Biology, the Department of Chemistry, 
and The Skaggs Institute for Chemical Biology.

On the voyage of the HMS Beagle, Darwin collected and studied different species 
of finches on several of the Galapagos Islands. The finches differed in their 
beak structure — some had thick, strong beaks and others had thin, delicate 
ones. Darwin observed that the different finches were each adapted for the 
specific types of seeds that served as their primary food source. The 
big-beaked birds were indigenous to the places where the big seeds grew; in 
areas where there were also small seeds, there were also small-beaked birds. 
Darwin reasoned that the finches had a common ancestor but had separated into 
different species — a classic concept in Darwinian evolution known as "niche 
partitioning," which holds that when two species are competing for resources 
within a common environment, they become differentiated so that each species 
adapts to use different preferred resources.

For several years, Joyce has been experimenting with a particular type of 
enzymatic RNA molecule that can continuously evolve in the test tube. The basis 
of this evolution comes from the fact that each time one of the molecules 
replicates, there is a chance it will mutate — typically about once per round 
of replication — so the population can acquire new traits over time.

Two years ago, Voytek managed to develop a second, unrelated enzymatic RNA 
molecule that also can continuously evolve. This allowed her to set the two 
RNAs in evolutionary motion within the same pot, forcing them to compete for 
common resources, just like two species of finches on an island in the 

In the new study, the key resource or "food" was a supply of molecules 
necessary for each RNA's replication. The RNAs will only replicate if they have 
catalyzed attachment of themselves to these food molecules. So long as the RNAs 
have ample food, they will replicate, and as they replicate, they will mutate. 
Over time, as these mutations accumulate, new forms emerge — some fitter than 

When Voytek and Joyce pitted the two RNA molecules in a head-to-head 
competition for a single food source, they found that the molecules that were 
better adapted to use a particular food won out. The less fit RNA disappeared 
over time. Then they placed the two RNA molecules together in a pot with five 
different food sources, none of which they had encountered previously. At the 
beginning of the experiment each RNA could utilize all five types of food — but 
none of these were utilized particularly well. After hundreds of generations of 
evolution, however, the two molecules each became independently adapted to use 
a different one of the five food sources. Their preferences were mutually 
exclusive — each highly preferred its own food source and shunned the other 
molecule's food source.

In the process, the molecules evolved different evolutionary approaches to 
achieving their ends. One became super efficient at gobbling up its food, doing 
so at a rate that was about a hundred times faster than the other. The other 
was slower at acquiring food, but produced about three times more progeny per 
generation. These are both examples of classic evolutionary strategies for 
survival, says Joyce.

Research for the article was supported by National Aeronautics and Space 
Administration (NASA), the National Science Foundation (NSF), and the Skaggs 
Institute for Research.

Journal reference:

   1. Sarah B. Voytek and Gerald F. Joyce. Niche partitioning in the 
coevolution of 2 distinct RNA enzymes. Proceedings of the National Academy of 
Sciences, Online April 28, 2009 [link]

Adapted from materials provided by Scripps Research Institute.
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Scripps Research Institute (2009, April 30). Evolution In A Test Tube: 
Scientists Make Molecules That Evolve And Compete, Mimicking Behavior Of 
Darwin's Finches. ScienceDaily. Retrieved May 1, 2009, from­ /releases/2009/04/090429140849.htm

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