In a nutshell, a group from the University of Minnesota "made" a multicellular organism in their lab. Essentially, they took a flask of plain ol' yeast and shook it to disperse the yeast cells, and then let any clumps of yeast settle to the bottom. Then they removed the top layer of yeast, leaving only the larger clumps left on the bottom. In this way they selected for yeast that were more likely to clump together. After repeating this about 60 times, they were left with clumps of snowflake-like balls of yeast.
|Ratcliff WC, et al. PNAS|
Amazingly, these "snowflake yeast" acted like a multicellular organism. Most strikingly, some of the cells in the cluster purposely killed themselves so that the cluster as a whole had a better chance to survive, a kind of behavior that is typical for multicellular organisms. The snowflake yeast also reproduced and had juvenile and adult stages. The video below shows one of the snowflakes yeast clusters reproducing:
This study really blows my mind. It's incredible to think that something as simple as shaking a flask of yeast could be enough selective pressure to encourage yeast to become something more. As Jeff Goldblum said in Jurassic Park, "Life will find a way."
If you have the time, I fully recommend reading a bit more on the subject from any of the following science blogs (all excellent):
Yeast suggests speedy start for multicellular lifeby Ed Yong from Nature News
How I became we, which became I again by Ed Yong from Not Exactly Rocket Science
Multicellular Life Evolves in Laboratory by Brandon Kiem from Wired Science