The evolutionary transition between single-celled organisms and multicellular life as we know it took several billion years to occur in nature, but under artificial pressure, evolutionary biologists have been able to make it happen in 60 days.
Single-celled yeast became multicellular creatures, a crucial step for life’s progression, from algae and bacteria to more complex forms of life. While this doesn’t duplicate what happened in the prehistoric transitions, it could help evolutionary biologists reveal the principles that guided them.
In the new study, published on January 17th in the Proceedings of the National Academy of Sciences, researchers led by evolutionary biologists Michael Travisano and William Ratcliff from the University of Minnesota grew brewer’s yeasts in flasks of nutrient-rich broth.
The experimental protocol was quite simple: once per day, they shook the flasks, removed the yeast that settled at the bottom and used it to start new cultures. Free-floating yeast was left behind, while yeast gathered in heavy, falling clumps survived to reproduce. Within a few weeks, the individual yeast cells were still single-celled, but clumped together. After two months, they came to a permanent arrangement. Each strain evolved to become multicellular, displaying all of the characteristics of complex forms of life.
The cells cooperate, and this cooperation benefits all of the cells involved. They gave a single-celled organism reason to become multicellular, and proved that this was what happened experimentally. Rapid evolution could occur in nature, it just needs to be discovered.
The multicellularity was engineered via artificial selection, but there is no reason why this couldn’t have happened in nature.
[via Wired, images by Ratcliff et al./PNAS]