Studies on yeast show that multi-cellular organisms evolved rather quickly, solving an 800-million-yr-old puzzle about where animals, plants came from
Mumbai Mirror Bureau
Posted On Wednesday, January 18, 2012 at 02:11:23 AM
More than 500 million years ago, single-celled organisms on Earth’s surface began forming multi-cellular clusters that ultimately became plants and animals. Just how that happened is a question that has eluded evolutionary biologists. Now scientists have replicated that key step in the lab using common Brewer’s yeast, a single-celled organism. The yeast “evolved” into multi-cellular clusters that work together cooperatively, reproduce and adapt to their environment – in essence, they became precursors to life on Earth as it is today. The results are published in this week’s issue of the journal Proceedings of the National Academy of Sciences. “The finding that the division-of-labour evolves so quickly and repeatedly in these ‘snowflake’ clusters is a big surprise,” says George Gilchrist of the National Science Foundation, which funded the research. “The first step toward multi-cellular complexity seems to be less of an evolutionary hurdle than theory would suggest,” says Gilchrist. “This will stimulate a lot of important questions.” In the beginning... It all started two years ago with a casual comment over coffee that bridging the famous multi-cellularity gap would be “just about the coolest thing we could do,” recalled Will Ratcliff and Michael Travisano, scientists at the University of Minnesota and authors of the paper. Then came the big surprise: it wasn’t that difficult. Using yeast cells, culture media and a centrifuge, it only took the biologists one experiment conducted over about 60 days. “I don’t think anyone had ever tried it before,” says Ratcliff. “There aren’t many scientists doing experimental evolution, and they’re trying to answer questions about evolution, not recreate it.” The results have earned praise from evolutionary biologists around the world. “To understand why the world is full of plants and animals, including humans, we need to know how one-celled organisms made the switch to living as a group, as multi-celled organisms,” says Sam Scheiner from NSF. “This study is the first to experimentally observe that transition, providing a look at an event that took place hundreds of millions of years ago.” How the experiment worked The scientists chose Brewer’s yeast, or Saccharomyces cerevisiae, a species of yeast used since ancient times to make bread and beer because it is abundant in nature and grows easily. They added it to nutrient-rich culture media and allowed the cells to grow for a day in test tubes. Then they used a centrifuge to separate the contents by weight. As the mixture settled, cell clusters landed on the bottom of the tubes faster because they are heavier. The biologists removed the clusters, transferred them to fresh media, and agitated them again. Sixty cycles later, the clusters – now hundreds of cells – looked like snowflakes. Analysis showed that the clusters were not just groups of random cells that adhered to each other, but related cells that remained attached following cell division. That was significant because it meant that they were genetically similar, which promotes cooperation. When the clusters reached a critical size, some cells died off in a process known as apoptosis to allow offspring to separate. In order for an organisms to form, most cells need to sacrifice their ability to reproduce, an action that favours the whole but not the individual. |
it is an intelligent -guided evolution,the same guided evolution may be taking place in billions of planets through out the universe
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