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It's ALL THINGS CONSIDERED from NPR News. I'm Audie Cornish. Scientists usually design experiments that will get them the answer to a question as quickly as possible, but every now and then, researchers ask a question that will take a long time to answer, longer than a human lifetime. That means they will never see the results of the experiment. As NPR's Nell Greenfieldboyce reports, it also means scientists have to think about how to keep the experiment going after they die.

NELL GREENFIELDBOYCE, BYLINE: There is a lab at Michigan State University in East Lansing where a brief, tedious chore must be done every day.

RICHARD LENSKI: And today will be day number - I think it's 8,449.

GREENFIELDBOYCE: That's nearly a quarter of a century. Richard Lenski opens up an incubator and pulls out some old friends, a dozen glass bottles full of bacteria. Lenski has been following these bacteria since 1988 to watch their evolution happen in real time. The bacteria reproduce so rapidly that in one day, they speed through seven generations creating the equivalent of their great, great, great, great-grandchildren.

Lenski brings the flask to a lab bench to feed his bacteria. He has blue eyes and a beard that's streaked with gray.

LENSKI: When I started this experiment, I didn't need reading glasses. And now, looking at things close-up is obviously more work than it used to be.

GREENFIELDBOYCE: Lenski is different than most evolutionary biologists. They look backwards in time, trying to understand how life came to be the way it is today. But Lenski has been looking forward to ask this question: Does evolution always take you to the same end point? If you started with 12 identical flasks full of identical bacteria, would they all change over time in the same way? Or would random mutations send each bottle's population spinning off in a different direction?

LENSKI: This was an experiment that was intended to be a long-term experiment, although I had no idea that it would be multiple decades.

GREENFIELDBOYCE: What happened was this: For the first decade, the bacteria in each flask mostly changed in similar ways, then the changes started to taper off. Lenski had other projects going on in his lab. Maybe he'd learned all he could from this one.

LENSKI: And so I was sort of thinking, OK, maybe it's time to stop the experiment. And I talked to a few colleagues. What do they think about that idea? And they basically said, no, you can't stop it. It's gone on too long.

GREENFIELDBOYCE: So he stuck with it. And he's glad because a few years later, in 2003, Lenski's lab noticed that the liquid in one flask looked strange.

LENSKI: This flask was considerably more cloudy. I was suspicious that we had a contaminant.

GREENFIELDBOYCE: But that wasn't it. The bacteria in that one flask had changed in a dramatic way. After 30,000 generations, they had gained the ability to consume a chemical that had always been in the flasks, but that was never intended to be a food. What's more, Lenski was able to trace exactly how that new trait emerged. Over the years, he's been freezing samples of his bacteria, so he was able to go back and track every little genetic change that's taken place through the generations using technologies that didn't even exist when he first started the study.

Lenski says this experiment has turned into a unique opportunity to study how evolution works in exquisite detail. Who knows how these flasks of bacteria might change way, way in the future?

LENSKI: I would really like the project to go on, not just for 50,000 bacterial generations. I'd like to see it go on for 50,000 human generations and really get some very hard numbers on the process of evolution.

GREENFIELDBOYCE: Now, Lenski won't be around to see those numbers. I asked if making plans for a really long-term study had changed the way he thinks about his own death.

LENSKI: Not really. Yeah, I think the - so my wife and I were very fortunate that one of our daughters had a baby about 20 months ago. And that really changes one's perception of time even more than a long-term experiment.

GREENFIELDBOYCE: He says people tend to conflate the universe with their own existence.

LENSKI: But having children, grandchildren and so on, that kind of - you really just come to grips with the vast span of time that is available. And we only get to occupy a tiny portion of it.

GREENFIELDBOYCE: Lenski is 56 years old. His career has got about another decade, then he'll find someone to inherit this project.

LENSKI: They might be in their, you know, early or mid-30s, and then they can decide whether they want to do it for just the next five or 10 years or whether they want to continue it for another 30 years and perhaps pass it on to somebody who hasn't even been born yet.

(SOUNDBITE OF CHIME)

GREENFIELDBOYCE: By coincidence, just across campus, there's a scientist who's taking care of an experiment that started long before he was born. Frank Telewski runs Michigan State University's botanical garden. He's also in charge of a study that began near this bell tower way back in 1879.

FRANK TELEWSKI: Not too far away from where we're standing, Professor Beal first dug a hole and buried the Beal bottles.

GREENFIELDBOYCE: These glass bottles, the Beal bottles, contain seeds. A botanist named William Beal buried them here because local farmers had been asking, if we weed our fields year after year, will we ever reach a point where the weeds just don't come back?

TELEWSKI: Well, that was a very interesting question. So, you know, Beal came back to the lab and he said, gee - he probably didn't actually say that, but, you know, probably thought, you know, what can we do for an experiment to see how long these seeds remain viable in the soil?

GREENFIELDBOYCE: So Beal put a precise quantity of seeds from a couple dozen different species into 20 bottles and stashed them underground. The original plan was to dig up one bottle every five years and see what would grow.

TELEWSKI: Clearly, burying 20 bottles and only taking one out every five years, the plan was to go beyond Professor Beal's career, let alone Professor Beal's life.

GREENFIELDBOYCE: Telewski assumes it meant a lot to him.

TELEWSKI: He had to be passionate about it. You don't do something like this, you know, with that long-term desire without being passionate.

GREENFIELDBOYCE: Beal opened six bottles before he retired, then he passed the study on to a colleague, who passed it on to a colleague, who passed it on to a colleague, who passed it on to Telewski. The experiment has lasted longer than Beal ever intended because the caretakers extended it. Telewski dug up his first bottle 12 years ago.

He did it at night, with a flashlight, trying not to draw any attention to the secret burial spot.

TELEWSKI: It was very exciting to, you know, to think back that, you know, when was the last time somebody saw this seed? You know, it was Professor Beal and that was 120 years ago. For me that holds a level of significance, that holds a level of fascination, charm.

GREENFIELDBOYCE: And he says the mysteries of long-term seed viability remain scientifically interesting. Only two plant species sprouted from the last Beal bottle. Telewski can't wait to dig up the next bottle in 2020.

TELEWSKI: Is this going to be the year nothing's going to germinate? What will germinate? How much will germinate? Will something that hasn't germinated in 30, 40 years all of a sudden appear?

GREENFIELDBOYCE: Telewski says this kind of inherited experiment is unusual, but in another way, the whole of science is one big long-term effort. Every time a researcher records a careful observation or stashes a specimen in a museum, they make it possible for some unknown person of the future to pick up where they left off.

TELEWSKI: And isn't that wonderful that somebody, somewhere, thought forward enough to say, let's hold on to this, let's keep this experiment going, let's design this experiment to go on and see where it takes us?

GREENFIELDBOYCE: Telewski already has someone in mind to inherit the Beal study when he retires. He says, if all goes as planned, the experiment will probably outlive her too. Nell Greenfieldboyce, NPR News.

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