Replication of a Key Evolutionary Step

Scientists in the University of Minnesota's College of Biological Sciences claim to have replicated in the laboratory the jump from single-celled to multicellular organisms in  single-celled brewer's yeast. In their experiment the yeast formed multicellular clusters which work together, reproduce and adapt to environmental changes. Their results were published in the January 16 issue of Proceedings of the National Academy of Sciences.

Brewer's yeast also called Saccharomyces cerevisiae was chosen because of its abundance in nature the ease of its growth. The Brewer's yeast was placed in a nutrient-rich culture and allowed to grow for a day. The test tubes were then place in a centrifuge for the purpose of  to stratifying the contents by weight. Be of their weight cell clusters ended up on the bottom of the tubes. The cell clusters were then removed and transferred to a fresh media to grow them again. After sixty cycles they had clusters of hundreds of cells looking similar to spherical snowflakes. These clusters were more than groups of random cells adhering to one another but cells that remained attached following cell division. Once the clusters attained a critical size, some cells died off to allow offspring to separate. The offspring  then reproduced at the same size as their parents.

Travisano and Ratcliff wonder why this doesn't occur more often in nature given how easy this was done in the  lab. Perhaps the answer is that this does not occur n nature because the conditions under which it occurred dose not occur in nature. Contrary to claims that they used natural selection, the did not. What they did was artificially select of larger clusters. Further more there is no evidence that the yeast cells in the clusters were any different genetically than ordinary brewer's yeast so where is the evolution?  Now this is an interesting study that show that Brewer's yeast will form cooperative clusters when forced to by a centrifuge and nothing more. This is clearly a capacity that has long existed in yeast but that it needs extreme conditions to occur.



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