Test Tube Yeast Evolve MulticellularityBy watching evolution in progress, scientists reveal key developments in the evolution of complex life and put evolutionary theories to the test
By Sarah Fecht | January 16, 2012
The transition from single-celled to multicellular organisms was one of the most significant developments in the history of life on Earth. Without it, all living things would still be microscopic and simple; there would be no such thing as a plant or a brain or a human. How exactly multicellularity arose is still a mystery, but a new study, published January 16 in Proceedings of the National Academy of Sciences, found that it may have been quicker and easier than many scientists expected.
"This is a significant paper that addresses one of the most fundamental questions in evolutionary and developmental biology," says Rick Grosberg, an evolutionary biologist at the University of California at Davis, who was not involved with the research.
Since evolution acts on individual cells, it pays off for a cell to be selfish. By hogging resources and hindering neighbors, a cell can increase the odds that more of its own genes get passed into the next generation. This logic is one of the reasons it has been challenging to imagine how multicellularity arose; it requires the subjugation of self-interest in favor of the group’s survival.
"Traditional theories make this out to be a difficult transition because you have to somehow turn off selection on the individual cells and turn it on for the collective," says Carl Simpson, a paleobiologist at the Museum für Naturkunde in Berlin, Germany, who also was not involved in the research. "The big result here is that these transitions can be super easy."
In the new paper, researchers at the University of Minnesota at Minneapolis used a simple but elegant technique to artificially select for multicellularity in yeast. They dumped unicellular yeast into a tube of liquid food and waited a few minutes for the cells to settle. Then they extracted the lowest fraction of the liquid and allowed whatever cells it contained to form the next generation. Because the cells had to cluster together in order to sink to the bottom and survive, the artificial selection made it more advantageous for yeast to cooperate than to be solitary.
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