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Your bread dough can be a unique and beautiful snowflake.

June 23, 2011

Photo by Moff

In evolutionary biology, there’s a huge landmark known as multicellularity. At some point in time, the unicellular organisms on Earth made the leap to multicellular organisms, which in turn opened the door to more and more complex living things, and the rest is history. Unicellular organisms independently made the jump to multicellular no less than 20 times in Earth’s history, most recently 200 million years ago, and leading to the wide array of animal and plant life that exists today.

Since so many organisms evolved to the multicellular stage, it’s hard to pinpoint exactly how this happened. One idea is that a bunch of cells working together, like a complex colony of bacteria, simply blobbed together into a big slug. This amoeba-like mass is called a grex, which totally sounds like the new character for Mass Effect. Anyhow, like a slime mold, this grex is now effectively a multicellular organism, using the scientific idiom, “If it looks like a duck…”

But getting back to why I have a picture of smiley bread at the top of this post. William Ratcliff and colleagues at the University of Minnesota in St Paul set out to evolve multicellularity in a common unicellular lab organism, brewer’s yeast. And they succeeded.

Their approach was simple: they grew the yeast in a liquid and once each day gently centrifuged each culture, inoculating the next batch with the yeast that settled out on the bottom of each tube. Just as large sand particles settle faster than tiny silt, groups of cells settle faster than single ones, so the team effectively selected for yeast that clumped together.

Sure enough, within 60 days – about 350 generations – every one of their 10 culture lines had evolved a clumped, “snowflake” form. Crucially, the snowflakes formed not from unrelated cells banding together but from cells that remained connected to one another after division, so that all the cells in a snowflake were genetically identical relatives. This relatedness provides the conditions necessary for individual cells to cooperate for the good of the whole snowflake.

Basically they created an environment in which only multicellular organisms could thrive and survive. So the yeast adapted and evolved into a new form of life to live.

Now, some people are saying that these are just colonies and not whole new organisms, or that at some point this yeast was in fact a multicellular organism that never lost that “clumping” trait. But the fact remains that this is pretty damn cool, and amazing how fast and easy it was to do, and Ratcliff is prepared to replicate his experiment with a form of algae that has never been multicellular.

Of course, unicellular life still outnumbers us multicellulars. In the words of molecular biologist Nicole King, “… unicellular life is the most successful, but that multicellular life is the most beautiful and dramatic.”

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