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Okay, so: I was understandably incredulous to read this. 41,000 years is unheard of in terms of an organism surviving deep freeze, by orders of magnitude. So, I went to the source.
I found a paper in a journal called Doklady Biological Sciences. It’s a collection of Russian microbiological articles translated to English.
A find like this, if verified, would probably end up in one of the top journals in the world: Nature, Science, maybe PNAS (which often publishes the more controversial theories). That’s not to say Russian journals aren’t good, but there’s a very strong English bias in science.
I’m going to get access to the pdf so I can read the original study, and report back. How do they know the nematodes weren’t modern? How was the sample dated?
In the meantime, I caution against credulously accepting this study (from last October) as fact just yet!
Here’s a link to the article (I meant to share it early, whoops!): Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland: link.springer.com/article/10.113…
Okay! I've acquired a pdf of Shatilovich et al. 2018, the paper that describes the findings of viable nematodes from 30,0-00-40,000-year old permafrost. Let's do this.
The authors analyzed "more than 300 samples of permafrost of different ages and origins, buried soils, and fossil rodent burrows."
Of those, only TWO "were shown to contain viable nematodes."
But what's a nematode, you ask?
Of those, only TWO "were shown to contain viable nematodes."
But what's a nematode, you ask?
Nematodes are roundworms -- unlike flatworms, they have a tubular digestive system. They're a diverse group of tiny animals that are found in just about every ecosystem, including salt water, fresh water, and soils. Many species are parasites (including to plants and people).
The ubiquity of nematodes is one of the reasons why we should be super skeptical of this study from the start. Nematodes infect people via their eggs; we ingest them in contaminated water or food.
Nematode eggs are tiny -- ~50 micrometers on average. A micrometer is 1/1000th the size of a millimeter. A millimeter is roughly the thickness of a credit card.
Okay, back to the ice age. The two samples that supposedly contained viable nematodes came from two deposits: an ancient ground squirrel burrow that had previously been dated in another study, and permafrost composed of glacial deposits that had been cored and dated.
Both samples were dated using radiocarbon dating. I haven't read the burrow paper they cite, but presumably they dated plant material in the burrow, and not the soil of the borrow (which may be much older than the burrow itself).
Radiocarbon dating lets us tell when something died and stopped taking new carbon into its body. Plants take up carbon dioxide as part of photosynthesis, and animals eat the carbon in plants or other animals.
The carbon dioxide that plants take up contains a mix of stable carbon (carbon-12) and an unstable isotope (carbon-14, or 14C). 14C has a half-life of 5,730 years -- that means every 5,730 years, you have half as much 14C, while the 12C stays the same.
That ratio (how much 12C to 14C) tells us how long ago an organism died (as long as it died within the last ~60,000 years, after which there wouldn't be any 14C left to measure, so radiocarbon dating isn't how we date very old things).
The permafrost sample contained partially decomposed plant remains, but it's not clear what exactly was dated -- the plants? A bulk sample of soil (which can contain carbon that's of mixed age due to mixing by roots and animals)?
The permafrost sample was dated at the University of Arizona lab, and gave an age of 41,700 ±1400. It's important to note that the nematodes themselves were not dated -- the soil sample was dated.
"Viable nematodes were isolated from permafrost by the method of enrichment culture." That means they didn't sieve to screen for eggs or adult nematodes. They took 1-2 grams of frozen soil, added liquid nematode food, and heated to room temperature for several weeks.
This is crucial, because from what I can tell reading this paper, we have no supporting evidence that the nematodes originated in the sediment and aren't modern contamination. Nematodes can be found in tap water, or even commercial growth medium (the liquid nematode food).
Nematodes can survive in harsh conditions, including freezing. There's a record of Antarctic nematodes surviving below-freezing temperatures for 25 years. But that's very different from tens of thousands of years frozen solid.
Right now, as an ice age ecologist, I have no confidence that these are real ice age nematodes, and not modern nematodes that got into two out of >300 samples. Journalists should not be reporting this finding as a credible fact unless and until we get a lot more information.
I'm taking a break to do some lab chemistry and have lab meeting (where we're talking about a paper that discusses the uncertainties and biases in the paleorecord, ironically!).
After the break, I'll talk about a credible ice age resurrection: a tiny Arctic plant grown from a 30,000-year old seed!
I'm back! Before we talk about adorable Arctic campion, folks have been asking some questions about the nematode study. First, why is this claim surprising, given that we know nematodes can use dormancy as a way to hang out in extreme conditions?
Permafrost environments are incredible for preservation. Some of the permafrost mummies have fur, stomach contents, feathers, whiskers, skin, urine, blood, everything. Some organisms look like they died just a few days ago.
As an example, check out this extinct cave lion cub from Siberia. It's about the same age as the permafrost samples that the nematodes were associated with -- about 30,000-40,000 years old. It's incredibly pristine -- the best-preserved mummy I've ever seen in my career. 
Even these mummies, with their amazing preservation, HAVE NO INTACT CELLS. It's what makes bringing mammoths back from cloning basically impossible (using the technique that was used to clone Dolly the sheep). See @bonesandbugs' talk on this for more info:
No intact cells (or DNA) means no cloning for extinct animals. Now, those mummies are all organisms that died before they froze, so it's possible that some living organisms (or their eggs) with adaptations like dormancy could use those strategies to survive extended freezing.
The broader point, though, is that freezing is bad for tissues. It breaks up cells. So even though that cave lion cub looks remarkably good for being over thirty thousand years old, its cells have been shredded to bits.
This point -- that freezing is bad for living things -- doesn't mean there's no chance of resurrecting ice age nematodes. As I said, lots of organisms have tools to resist freezing damage (mammoths had a neat hemoglobin that acted like an antifreeze in their blood!).
What it does mean is that we have to be certain beyond a reasonable doubt that the nematodes came from the sediments themselves, and not from a contaminated source (e.g., water, growth medium). So how can we do better?
We can't date the nematodes themselves, because they've been gobbling up modern carbon in the lab. That means even if they were from ice age eggs or frozen adults, they'll date as modern or at least much younger than the permafrost (assuming they weren't accidentally introduced).
The first thing I would do is sieve permafrost sediment in controlled conditions to look for nematodes or their eggs, ensuring no prior exposure to any modern water, no lab contamination in tap water or nematode food, etc.
Then, if I found eggs or worms in samples that also had viable nematodes, I'd try to collect enough eggs or worms from just-thawed sediment to be able to get a radiocarbon date the organisms directly.
There are lots of reasons why an organism might be older or younger than the soil you find it in. Soil can contain old carbon from bits of dead stuff that hasn't decomposed, or very young carbon from roots, burrowing insects or animals, or mixing (like from freezing and thawing).
There ARE a couple of examples of organisms that have been resurrected! The first is a "giant" (ha!) virus. Here's the paper: pnas.org/content/112/38… And here's a nice write-up by @edyong209: nature.com/news/giant-vir…
Viruses are different from nematodes, though -- first, they're MUCH smaller, so they may be able to survive better in frozen soils (permafrost). Secondly, they don't really have proper cells (some scientists argue they're not technically alive!).
The second example is a 32,000-year-old campion (Latin name Silene), a cute little Arctic flower that was grown from a seed found in a ground squirrel's burrow. Here's the original study: pnas.org/content/109/10… And here's a blog post I wrote at the time: contemplativemammoth.com/2012/02/24/con…
The Silene example is super cool -- the previous record-holder for the oldest cultivated seed was 2000 years old. They also dated the fruits of the plants from the same burrow, so we know they're ancient and not modern. A+!
This experiment wasn't like growing a bean in a cup in your elementary school science class, though. They had to stimulate the seed with some hormones and do a little bit of extra science to get them to grow. But they did, and made plants that themselves produced viable seeds!
Right now, you might be thinking, "WAIT A SECOND, GILL. You explained all about how animal cells get shredded by freezing, and viruses don't have cells. Fine. But plants are alive, and they have cells. What gives?"
What gives, my friends, is that plants are AWESOME.
In all seriousness, many seeds can do the same dormancy thing that nematode eggs can do. It may be that having a cell wall (which plants have but animals don't) helps, and there are hormones in seeds that help them to survive cold: gazettenet.com/earth-matters-…
To conclude (for now): until we know for certain that nematodes grown from permafrost soil samples are actually old, and not modern, we can't say anything about resurrecting frozen ice age worms.
If you're currently freaking out about the idea of ancient diseases thawing out of permafrost, you might enjoy this short thread:
P.S. As someone mentioned, if you fed modern nematodes only ancient plants, etc., that would make them seem older than they are if you dated them! So you'd have to ensure you were dating frozen nematodes that were definitely from the permafrost, and not contamination.
P.P.S. Seeds are alive, but dormant, so my very first tweet was misleading -- I meant a living, non-dormant organism being frozen and thawed and still being alive.
P.P.P.S. I completely missed a really obvious way to check for contamination -- negative controls! E.g., run sterilized soil (or similar nematode-free stuff) through the same treatments. If you still get nematodes, that means there's contamination. Thanks, @LSE_Angela!
P.P.P.P.S. If there's a betting pool for animals that could survive 40,000 years being frozen, nematodes would definitely be a candidate. It's not that the findings are impossible, they're just extraordinary, so proceed with skepticism until further notice.
I’d also like to link here to a thread by @BurOak5, a journalist who write about this study. He was really open about his thought process as a journalist covering the story:
I don’t want to shame anyone for being excited about this story. It’s easy for me to nerd out about the nitty-gritty if the methods, but there’s also wonder and discovery here, too, no matter how old the nematodes end up being.
Never feel bad for being excited about science!
Never feel bad for being excited about science!
