622981 external_news 1562161561 1562168859 Billions of years ago, life crossed a threshold. Single cells started to band together, and a world of formless, unicellular life was on course to evolve into the riot of shapes and functions of multicellular life today, from ants to pear trees to people. It's a transition as momentous as any in the history of life, and until recently we had no idea how it happened. The gulf between unicellular and multicellular life seems almost unbridgeable; a single cell's existence is simple and limited. "This is what evolution always does, makes use of things that are around for new purposes," says William Ratcliff, an assistant professor in the School of Biological Sciences at Georgia Tech. That thrifty repurposing may explain the swift transitions that have unfolded in Ratcliff 's lab. Instead of looking at the fossil record or comparing genomes of existing organisms, he has recreated evolution in lab cultures. "My own research has been not to try to find out what happened in the real world, but to look at the process of how cells evolve and increase in complexity," he explains. As cells banded together in lab cultures, they didn't just put existing genes to new uses. Studies of Volvox, an alga that forms beautiful, flagellated green balls, shows that multicellular organisms also found new ways to use existing functions. "What this group of algae has taught us is some of the steps involved in the evolution of a multicellular organism," says Matthew Herron, an evolutionary biologist in the School of Biological Sciences at Georgia Tech.

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