Previous: Why Animals Keep Self-Amputating
Next: Why Are Periodical Cicadas So ... Periodical?



View count:217,400
Last sync:2022-10-29 15:00
This episode is brought to you by the song Like This -- Patrick Olsen’s new single. It’s available now on all streaming services.

Tiny creatures called rotifers seem to have no problem continuing their lives after waking from a refreshing 24,000-year nap. And DNA samples from goats that lived 30,000 years ago tell us a bit about how humans were managing them back then.

Hosted by: Hank Green

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Alisa Sherbow, Silas Emrys, Drew Hart. Jeffrey Mckishen, James Knight, Christoph Schwanke, Jacob, Matt Curls, Christopher R Boucher, Eric Jensen, Adam Brainard, Nazara, GrowingViolet, Ash, Sam Lutfi, Piya Shedden, KatieMarie Magnone, charles george, Alex Hackman, Chris Peters, Kevin Bealer, Jason A Saslow

Looking for SciShow elsewhere on the internet?

This episode is brought to you by the song Like This.

Patrick Olsen’s new release single. You can check out the link in the description to start listening. [♪ INTRO].

Imagine taking a nap at a time when woolly mammoths roamed the plains… and then waking up in the twenty-first century. That may sound like a science fiction story, but it might be the real experience of tiny aquatic animals called rotifers. According to a report in Current Biology, these little creatures can survive being frozen in ice for at least twenty-four thousand years.

Seems like too long. Rotifers are microscopic invertebrate animals, usually less than one millimeter long. They live in wet environments all over the world, including moist soils.

And we already knew that they could survive being frozen. Experiments have shown that rotifers can remain frozen for up to ten years before thawing out and just continuing to live their tiny lives. But maybe ten years is nothing for a frozen rotifer.

Researchers found these Rip Van Rotifers in a sample of frozen soil, or permafrost, from northeastern Siberia. The soil sample came from three and a half meters underground, and radiocarbon dating estimated it to be around twenty-four thousand years old. Like, imagine sleeping so long you have to be radiocarbon dated when you wake up.

When the researchers thawed the soil, they found living rotifers inside. Now, it’s possible for something as small as a rotifer to have like maybe snuck into the soil after it originally froze, or even during the sample collection, but the scientists claim this is not the case here. First, because the icy soil is solid enough that even something as tiny as a rotifer shouldn’t have been able to squeeze in.

And second, because they identified fragments of DNA within the frozen soil that matched with the rotifers. This evidence seems to suggest that the tiny animals were frozen all that time. Yet, these rotifers weren’t only able to keep on living, they began reproducing.

Since rotifers reproduce asexually, that meant the researchers had a convenient culture of rotifer clones to study. They were able to compare these ancient rotifers’ DNA to more modern specimens, and it looks like they are probably distinct from the rotifers wiggling around today. And they were also able to run a series of experiments, re-freezing the cloned rotifers and showing that they are fully capable of surviving being slowly frozen into ice.

Like many other rotifers, they appear to have some sort of mechanism that prevents their cells and tissues from being damaged or destroyed by ice crystals, though researchers don’t know how that works yet. Amazing as all of this sounds, these aren’t the first multicellular organisms reported to survive thousands of years of deep freeze. A 2018 study reported a pair of nematode worms that survived being frozen in permafrost for over thirty thousand years.

And a 2012 study reported plant seeds that were able to germinate after being frozen for nearly thirty-two thousand years. Now, it’s worth pointing out that these previous studies have drawn skepticism from other scientists, who worry that they haven’t fully ruled out the possibility of contamination by modern organisms. But it’s definitely true that rotifers and other organisms can survive being frozen for long periods of time … possibly very long periods.

Scientists are hopeful that studying these organisms might help us develop better techniques for storing frozen tissues and organs. So if you’re clinging to the sci-fi dream of freezing yourself for thousands of years into the future, the secret to success might be held within these tiny invertebrates. And if those rotifers really were frozen for twenty-four thousand years, they totally slept through a major historical event the domestication of goats!

That’s right, that was our transition. Humans started domesticating crops and livestock around ten thousand years ago, and it was a pretty big deal for us as a species. Goats were one of the ones we started with.

But there’s a lot we don’t know about the early parts of that process. And now that picture is a little bit clearer. A new study in the journal PNAS reports ancient goat DNA from a time when they were just beginning their path to domestication.

The DNA samples come from remains of goats in two archaeological sites in the Zagros mountains of western Iran, dating to about ten thousand years ago. Researchers were able to sequence DNA from thirty-two goats at these sites. To date, these are the oldest livestock genomes ever sequenced.

The results show a group of animals that were not fully wild, but weren’t fully domesticated yet either. The physical remains of these goats look a lot like their wild cousins, with large bodies and big, scimitar-shaped horns. And their DNA is lacking some of the genetic signs associated with domestication, including changes in genes linked to coat color.

But they were clearly on the way the analysis found that most of these ancient goats represent an early branch of the domestic goat lineage. Amazingly, these goats’ DNA held clues to how humans were managing them a mixture of modern and ancient practices. See, some of the sampled goats were genetically very similar to wild goats, so it seems that humans of the time were still in the habit of capturing wild goats to add to their herds.

But on the other hand, the Y chromosomes of these goats, which are passed down by males, were much less diverse than mitochondrial genomes, which are passed down by females. This suggests the ancient herders were in the habit of culling most males and reserving only a select few for breeding, a practice still used today by goat herders of that region, and also by animal breeders all over the world. Altogether, this reveals a picture of a transitional period in goat domestication.

Ten thousand years ago, humans were already managing goats as livestock, using some of the same strategies as today. But it would still be some time before they were the domesticated animals we know today: crucial sources of food, milk, and also hilarious internet videos. But in addition to hilarious videos, the Internet also has music.

And today’s sponsor, Music for Scientists by Patrick Olsen, has a bunch of songs you can choose from. Such as the new single, Like This! This is a fun catchy single that focuses on our place on Earth.

It’s a total banger that’s all about seeing very familiar things in new ways. If you want to check this new single out, check out the link in the description to start streaming Like This by Patrick Olsen. [♪ OUTRO].