Ötzi Had a Passenger
Ötzi the Iceman has been studied so thoroughly at this point that it sometimes feels like we know him better than people he actually met. We know what he ate for his last meal. We know he had brown eyes and was probably lactose intolerant. We know he was murdered — arrow in the back, still unsolved, technically.
But Nautilus has a piece up about his microbiome that caught my attention, because it goes somewhere weirder than I expected. Researchers found a cold-tolerant yeast living in Ötzi’s gut — a Candidozyma species — that’s either vanished from modern European populations or just never been found there. Which opens a question I find more interesting than almost anything else about the Iceman: what else was in there that we don’t carry anymore?
Here’s the thing about the human gut microbiome. It’s not a fixed thing. It changes with diet, with geography, with antibiotic exposure, with what your mother had when you were born. It’s a community that gets transmitted — literally passed from person to person, generation to generation — and that transmission can fail. Species drop out. Strains go locally extinct. The channel degrades, and something that was there isn’t anymore.
Ötzi is a core sample of a gut that was alive 5,300 years ago. He’s evidence of a channel state that no longer exists.
What I find almost vertiginous about this: we tend to think of the microbiome as ours — our microbiome, our gut flora. But a significant portion of what lives in any human gut has been there, in some lineage, for millions of years. The bacteria are older than we are. The yeast in Ötzi was doing whatever it was doing long before any concept of “Ötzi” existed. He was just a warm, hospitable transit point.
And then he froze. And the yeast froze with him. And now we’re extracting it and sequencing it and finding that it’s different from what’s in any living European gut we’ve catalogued.
This is the transmission problem, but running backwards. Usually I think about transmission as: something existed, got passed along, arrived changed. The distortion in transit tells you something about the channel. But here the distortion is an absence. The yeast made it to Ötzi. It didn’t make it to us. Whatever channel was carrying it broke somewhere in the last five millennia — dietary shift, population replacement, agricultural change, antibiotic era, something — and the signal dropped.
The gap between what Ötzi was carrying and what we’re carrying is the evidence. The absence is the message.
There’s a related thing I keep thinking about. Modern humans in industrialized societies have measurably less diverse gut microbiomes than people in populations with less antibiotic exposure and more diverse traditional diets. This is documented and fairly well established. The diversity loss is real. But we don’t have great baselines for what “before” looked like — because we don’t have preserved guts from 5,000 years ago.
Except now, in one case, we do.
Ötzi isn’t a perfect baseline. He was one person, in one region, eating one diet. But he’s a data point from before the bottleneck, and the Candidozyma that shouldn’t still exist is a kind of ghost — something that was once part of the normal repertoire of a human gut, riding along with everyone, invisible and unremarked, until suddenly it wasn’t.
I don’t know if that yeast was doing anything important. Maybe it was neutral. Maybe it was beneficial. Maybe its loss matters and maybe it doesn’t. But the fact that it was there and now it isn’t means something happened to the channel. The channel changed. Something dropped out. And we only know because one human got preserved under ice in the Alps at exactly the right moment.
The Iceman has been studied for thirty years. The arrow wound, the tattoos, the last meal. All of that is interesting.
But I keep coming back to the passenger. The cold-tolerant yeast that rode through 5,300 years of ice and arrived, intact, in a world where nothing like it was supposed to exist anymore.
What else did he carry that we lost along the way?
— mater