58,000 generations of bacteria NEVER achieve perfection

Researchers have long known that organisms continue to develop if the environment continues altering, but they've previously believed that alteration would eventually stop if the environment remained the same.

According to a news release from Michigan State University, there’s no achieving perfection for the bacteria being grown in Richard Lenski’s lab at MSU.

For 25 years, Lenski’s experiment has produced more than 58,000 generations. Lead author Michael Wiser, an MSU graduate student, compares the evolving bacteria’s push for perfection to hiking.

“When hiking, it’s easy to start climbing toward what seems to be a peak, only to discover that the real peak is far off in the distance,” Wiser noted. “Now imagine you’ve been climbing for 25 years, and you’re still nowhere near the peak.”

In this case, the peaks are known as fitness peaks — when a population discovers the perfect number of mutations, so it can’t improve any more. Any new mutation that develops will make things worse. Amazingly, the bacteria in Lenski’s lab haven’t reached their fitness peak after 25 years, residing in the same environment.

Researchers have long known that organisms continue to develop if the environment continues altering, but they’ve previously believed that alteration would eventually stop if the environment remained the same.

Wiser gathered hundreds of samples from the deep freezer than holds a frozen fossil record — bacteria from the beginning of Lenski’s experiment. Unlike most fossils, these fossils are alive. They can be examined in contrast to samples from various generations to determine the path of the bacteria as they strove for perfection for 58,0000 generations.

“There doesn’t seem to be any end in sight,” Lenski posited. “We used to think the bacteria’s fitness was leveling off, but now we see it’s slowing down but not really leveling off.”

Wiser discovered that the path corresponded to a kind of mathematical function known as a power law. Although the slope of the power-law functions becomes less and less steep over time, it never achieves a peak.

“It was surprising to me that a simple theory can describe the entirety of a long evolutionary trajectory that includes initially fast and furious adaptation that later slowed to a crawl,” professed co-author Noah Ribeck, a MSU postdoctoral researcher. “It’s encouraging that despite all the complications inherent to biological systems, they are governed by general principles that can be described quantitatively.”

Is there an end in sight to this 25-year experiment?

“I call this the experiment that keeps on giving,” Lenski posited. “Even after 25 years, it’s still generating new and exciting discoveries. From the models, we can predict how things will evolve – how fit the bacteria will become – if future generations of scientists continue the experiment long after I’m gone.”