Photo: Umberto Brayj (Flickr)
Evolutionary changes occur slowly. Fossils indicate the evolution of reptiles into mammals spanned millions of years. Scientists have always thought the evolution of single-celled organisms into multi-cellular ones took eons as well. But maybe that wasn’t the case.
Researchers experimenting with a common brewer’s yeast think evolution from single-celled to multi-celled organisms might have happened in the blink of an eye on the geologic time scale.
Their experiment was simple. They grew yeast in ten parallel liquid cultures that were gently centrifuged each day. Because heavier particles settle to the bottom during spinning, this process separated yeasts that tended to clump from those that remained single. Each day, they saved some of the clumped cells and continued the procedure.
In essence, the scientists were taking nature’s place, selecting for yeasts that tended to become multi-cellular. After sixty days, or about 350 generations, every one of the cultures contained clumped cells known as “snowflakes.” The snowflakes were genetically identical relatives that remained connected to each other after cell division.
The cells not only stayed connected, after a few more generations they began to show division of labor. Some cells even died in order to allow daughter colonies to break off of the original parent.
Not all scientists are convinced by the experiment. They point out that brewer’s yeast was multi-cellular until the characteristic was bred out by laboratory propagation. The yeast may retain some multi-cellular genes to quickly revert to its ancient form.
In order to address these concerns, a second experiment is in the works. Scientists are investigating with a single celled alga that has no multi-cellular ancestor. We will have to wait and see how that turns out.