How was eDNA discovered?

Phil Sansom and Sally Le Page heard from founder of eDNA Eske Willerslev from the University of Cambridge about his discovery...

Phil - Eske, am I right that you wrote the very first paper on environmental DNA and sort of established this whole new field of genetics back in 2003?

Eske - I believe so. I mean, it was part of my doctorate, so I couldn't get my hands on any of these super famous fossils, you know, bones and teeth and stuff like that. So, I kind of thought I have to do something else. I thought, what can I do where people don't care about the material? And then I was sitting, looking out of the window, leaves falling down from the trees. It was autumn and there was a dog that took a c*** on the street?

Sally - Or to put it a little more delicately Eske, the dog defecated.

Eske - And I thought, well, we know that there's DNA in these things right from the animal or the plant. But we also know that after the next rainfall, the dog faeces will be gone. We also know after a few years the leaf will be gone, but the question is what will happen to the DNA? I thought, well, maybe it could survive in sediments. I went to my supervisor and said, I have this idea. Could DNA survive in sediments and both him and the rest of the professors laughed and said, we've never heard anything so stupid, but luckily I didn't give up actually. So, in the past, before I became a scientist, I was a trapper in Siberia and also did a lot of expeditions there.

Sally - Because all scientists have a background as fur trappers in Siberia.

Eske - But it became actually quite helpful because obviously I'd seen these permafrosts where it's frozen soil and we knew already then that cold temperatures are good for long-term DNA preservation. So, I got in touch with a Russian guy with some of these permafrost cores. Actually from the same areas where I had been running around as a trapper. I thought one would need an enormous amount of material to obtain DNA because what is the chance of an animal passing just across that particular area? So, I tried to work with very large, like kilograms of soil, but obviously you couldn't extract. There were no DNA extraction kits fitting that because everything people were doing at that time was retrieving DNA from bacteria. So, I tried to freeze-dry it and all kinds of stuff, and it didn't really work. And in the end, you know, I said, well, I'll just try with half a gram. And I took out this DNA and I remember it was like Christmas Day. Everybody had gone home from work and there, I got the results coming out of the sequencer and I blasted them. And, you know, I could see woolly mammoth DNA, horses, reindeer.

Phil - Woolly mammoth?

Eske - Yeah, yeah. This was ancient soil. It was like 20,000 years old.

Phil - You immediately found woolly mammoth DNA, which is pretty incredible. Did you expect it to work so quickly or was it a complete shock?

Eske - I didn't expect it to work that well. I thought that you would need a larger amount of materials to even then be lucky. Finding a mammal for example, would be like looking for a needle in a haystack. So, that's what I thought, but realised just from those early experiments, that was not really the case. We are in fact walking around on DNA from animals and plants, both in our contemporary settings, but also from the past. When those sediments were part of the surface 20, 30, 40,000 years ago. But nobody believed it for 10 years. I was almost the only one doing this stuff, for the following 10 years. And I remember they came to my dad and they just didn't believe it. I mean, they said, well, you know, it's not real. And until they went to the lab themselves, got a sample and tried.