Richard Lenski

Based on Wikipedia: Richard Lenski

On February 24, 1988, a scientist at the University of California, Irvine set up twelve flasks of E. coli bacteria. Nothing unusual about that—microbiologists culture bacteria every day. But Richard Lenski had something different in mind. He wasn't going to throw these cultures away after a week. He was going to keep them going, transferring a tiny fraction to fresh growth medium every single day, watching what happened as the bacteria reproduced generation after generation.

That was thirty-seven years ago. The experiment is still running.

Those twelve populations of bacteria have now passed 75,000 generations—the equivalent of roughly two million years of human evolution. And what Lenski and his colleagues have observed in those flasks has transformed our understanding of how evolution actually works, providing direct experimental evidence for processes that Darwin could only infer from fossils and living specimens.

The Man Behind the Longest Experiment

Richard E. Lenski was born in 1956 into what can only be described as an intellectually formidable family. His father was Gerhard Lenski, a prominent sociologist known for his work on social stratification and the evolution of human societies. His mother, Jean Lenski, was a poet. His great-aunt was Lois Lenski, the beloved children's author who won the Newbery Medal. And reaching further back, his great-grandfather was Richard C. H. Lenski, a Lutheran theologian whose Bible commentaries are still widely consulted today.

This lineage spanning science, literature, and theology would prove oddly fitting for someone whose work would later place him at the center of debates between evolutionary biology and creationism.

Lenski earned his undergraduate degree from Oberlin College in 1976, then completed his doctorate at the University of North Carolina in 1982. His postdoctoral work at the University of Massachusetts, Amherst, in Bruce Levin's laboratory, marked his entry into microbiology—the field where he would make his greatest contributions. After teaching at UC Irvine, he moved to Michigan State University in 1991, where he remains today as the John A. Hannah Distinguished Professor of Microbial Ecology.

Why Bacteria? Why Bother?

To understand what makes Lenski's experiment so revolutionary, you need to appreciate a fundamental problem in evolutionary biology: time.

Evolution happens slowly. Maddeningly slowly. When Darwin observed finches in the Galápagos, he could see the end products of evolution—different beak shapes adapted to different food sources—but he couldn't watch the process unfold. A human lifetime is simply too short to observe meaningful evolutionary change in most organisms.

Bacteria solve this problem elegantly.

E. coli can reproduce in as little as twenty minutes under ideal conditions. In Lenski's experiment, using more controlled growth conditions, each population goes through roughly six to seven generations per day. This means that within a single human year, Lenski can observe what would take millennia in a population of elephants or centuries in a population of humans.

There's another advantage too. Lenski can freeze samples of his bacteria at regular intervals. These frozen samples remain viable indefinitely—you can thaw them out years or decades later, and they'll wake up and start growing again as if no time had passed. This creates a "frozen fossil record" that allows researchers to go back in time. If you observe an interesting change at generation 50,000, you can resurrect ancestors from generation 40,000, 30,000, or even generation zero and watch evolution replay itself.

This ability to replay evolution would prove crucial for understanding one of the experiment's most dramatic discoveries.

The Great Citrate Breakthrough

Every biology student learns a simple rule about E. coli: it cannot use citrate as a food source in the presence of oxygen. This isn't just a casual observation—it's one of the defining characteristics of the species, used in laboratory tests to distinguish E. coli from other bacteria. If your bacteria can eat citrate aerobically, by definition it's not E. coli.

Except that around generation 31,500—roughly fifteen years into the experiment—something remarkable happened in one of the twelve populations, designated Ara-3.

Bacteria started growing to much higher densities than normal. When Lenski's team investigated, they found that these E. coli had done the impossible. They had evolved the ability to consume citrate in the presence of oxygen.

This wasn't a minor tweak. This was the evolution of a genuinely new trait, one that required multiple genetic changes working together. The researchers used their frozen fossil record to investigate: they revived bacteria from earlier generations and asked whether the ability to evolve citrate usage was pure chance or whether earlier mutations had somehow set the stage.

The answer was both. There seemed to be "potentiating" mutations that occurred earlier, making the later key mutation possible. Evolution wasn't just random—there was a historical contingency to it. The past constrained the future. The citrate breakthrough couldn't have happened in the early generations because the necessary precursor mutations hadn't yet accumulated.

This finding spoke directly to a famous question posed by the evolutionary biologist Stephen Jay Gould: if you could replay the tape of life from the beginning, would you get the same results? Lenski's experiment suggested the answer is complicated. Some adaptations occurred in all twelve populations—these seemed almost inevitable. But others, like the citrate mutation, occurred in only one population out of twelve, suggesting that evolution involves a significant element of chance.

Digital Evolution

As revolutionary as the E. coli experiment has been, Lenski recognized its limitations. Even with bacteria, certain questions are difficult to address. How do complex traits requiring multiple coordinated mutations evolve? How do populations navigate "fitness landscapes"—the abstract topography of better and worse genetic combinations?

To tackle these questions, Lenski collaborated with computer scientists Charles Ofria and Chris Adami on a project called Avida, a computer program that simulates evolution using digital organisms.

These aren't simulations in the usual sense, where programmers write rules about how evolution should work and then watch those rules play out. Instead, Avida creates genuine artificial life. Digital organisms—essentially small computer programs—reproduce by copying themselves. But copying is imperfect; random errors creep in, just as mutations arise in DNA replication. Some of these digital mutations help an organism reproduce faster, others slow it down, and most have no effect at all.

The organisms compete for computational resources in their digital petri dish. Those that can perform certain mathematical calculations earn bonus resources and reproduce more quickly. Natural selection favors any mutation that helps with these calculations, even though the original organisms had no calculating ability whatsoever.

What emerged from Avida was striking. Starting from simple self-replicators with no mathematical ability, complex calculating organisms evolved through the gradual accumulation of mutations, each building on previous changes. Ofria, Lenski, and their colleagues could trace the exact sequence of mutations that led to complex capabilities, step by step, providing direct evidence that sophisticated functions can evolve through natural processes.

The Conservapedia Affair

In 2008, Lenski found himself in an unexpected spotlight when Andrew Schlafly—son of the conservative activist Phyllis Schlafly and founder of Conservapedia, a right-leaning alternative to Wikipedia—wrote to demand access to Lenski's research data.

Schlafly was skeptical of the citrate evolution results and implied that Lenski might be hiding something. Lenski responded with a letter that became something of an internet legend—polite, thorough, and devastatingly methodical. He explained that his data was already publicly available in his published papers, that his methods were described in detail for anyone who wanted to replicate them, and that the bacteria themselves were freely available to any qualified researcher who wanted to examine them.

The exchange highlighted a fundamental misunderstanding about how science works. Schlafly seemed to expect a smoking gun that would either prove or disprove evolution. Lenski patiently explained that science proceeds through careful observation, replication, and peer review—all of which his work had undergone. The bacteria weren't going to confess to being created; they could only be studied using the methods of science.

This wasn't Lenski's last encounter with evolution's critics. In 2014, the creationist Ken Ham cited the citrate research in his famous debate with Bill Nye (of "Science Guy" fame), claiming it actually supported creationism. Lenski publicly criticized Ham's interpretation, pointing out that Ham had fundamentally misunderstood the work. The citrate evolution was precisely what evolutionary theory predicted: a new capability emerging through mutation and natural selection, not the creation of a new "kind" of organism as Ham suggested was required.

What Lenski Has Taught Us

After more than three decades, the Long-Term Evolution Experiment has produced insights that textbooks once only speculated about.

First, evolution is real and observable. This might seem obvious, but having direct experimental evidence, rather than just inferential evidence from fossils and comparative anatomy, matters. Scientists can point to precisely documented changes in gene sequences, watch new traits emerge, and measure fitness improvements generation by generation.

Second, evolution is partly predictable and partly not. All twelve populations have increased in fitness over time—that's predictable. They've all evolved faster reproduction in the specific growth conditions Lenski uses—also predictable. But they've gotten there by different routes, and some populations have evolved capabilities that others haven't, even after trillions of bacterial generations.

Third, the dynamics of adaptation are more complex than simple models suggest. Early generations saw rapid improvement, but the pace of adaptation hasn't stopped even after 75,000 generations. The populations keep finding new ways to improve, though the gains become smaller over time. This challenges older ideas that evolution would eventually "run out" of improvements to make.

Fourth, the experiment has revealed the phenomenon of clonal interference—when multiple beneficial mutations arise in the same population and compete with each other. In sexual organisms, different beneficial mutations can combine through recombination. In asexual E. coli, they're stuck competing, which complicates and sometimes slows adaptation.

A Living Legacy

The accolades for Lenski's work have been substantial. He received a MacArthur "genius grant" in 1996. He was elected to the National Academy of Sciences in 2006 and the American Philosophical Society in 2018. In 2010, he co-founded the BEACON Center—the National Science Foundation Science and Technology Center for the Study of Evolution in Action—which brings together evolutionary biologists, computer scientists, and engineers to study evolution across platforms, from bacteria to digital organisms to robots.

In 2021, the Society for the Study of Evolution awarded Lenski its Lifetime Achievement Award, recognizing a career spent not just observing evolution but fundamentally changing how we study it.

But perhaps the most remarkable aspect of Lenski's work is its ongoing nature. Every day, someone in his lab transfers those bacterial populations to fresh medium. Every day, the bacteria reproduce and occasionally mutate. Every day, the experiment gets a little longer, a little more informative.

There's no defined endpoint. Lenski has arranged for the experiment to continue even after he retires—it's become bigger than any one person. In 2013, he started a blog called "Telliamed Revisited" (Telliamed spelled backward is de Maillet, referring to an eighteenth-century precursor to evolutionary thinking) and began sharing updates on social media. A 2021 Veritasium video about the experiment garnered over six million views, introducing a new generation to this quiet but profound scientific achievement.

The experiment continues because evolution continues. There is always more to learn. Generation 80,000 will reveal things invisible at generation 75,000. Generation 100,000 will reveal things invisible at generation 80,000. In this sense, Lenski's greatest contribution may not be any single finding but the framework itself: the demonstration that evolution can be studied not just as history but as an ongoing process, observable in real time, in twelve flasks of bacteria that have been growing, adapting, and evolving for almost four decades.

Darwin had to infer evolution from its products. Lenski gets to watch it happen.