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In a bone-filled week, a rediscovered cranium from China might represent an entirely new species of human that's possibly our closest evolutionary relative. And, while studying a 5,000-year-old skeleton, scientists found evidence of what might be the earliest plague infection.

Hosted by: Hank Green
Thumbnail Credit: Chuang Zhao

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Sources:
Dragon Man
https://www.eurekalert.org/pub_releases/2021-06/cp-mf061721.php
https://www.cell.com/the-innovation/pdfExtended/S2666-6758(21)00056-4
https://www.cell.com/action/showPdf?pii=S2666-6758%2821%2900055-2
https://www.cell.com/action/showPdf?pii=S2666-6758%2821%2900057-6
Supplementary Material
https://www.cell.com/cms/10.1016/j.xinn.2021.100130/attachment/46d379ee-4fa5-409a-8096-18d1729ebd64/mmc1.pdf
https://www.nytimes.com/2021/06/25/science/dragon-man-skull-china.html

Plague
https://www.eurekalert.org/emb_releases/2021-06/cp-t5m062421.php
https://www.cell.com/cell-reports/fulltext/S2211-1247(21)00645-8?utm_source=EA

Images:
https://www.eurekalert.org/multimedia/pub/268201.php?from=506848
https://www.eurekalert.org/multimedia/pub/268199.php?from=506848
https://www.eurekalert.org/multimedia/pub/268200.php?from=506848
https://www.istockphoto.com/photo/anthropology-gm187614154-29109516
https://commons.wikimedia.org/wiki/File:Skhul.JPG
https://www.flickr.com/photos/101561334@N08/9929912223/
https://www.researchgate.net/figure/Family-tree-of-the-four-groups-of-early-humans-living-in-Eurasia-50-000-years-ago-and-the_fig1_326503956
https://commons.wikimedia.org/wiki/File:Yersinia_pestis.jpg
https://www.eurekalert.org/multimedia/pub/268944.php?from=507707
https://www.eurekalert.org/multimedia/pub/268945.php?from=507707
https://www.istockphoto.com/photo/plague-bacteria-yersinia-pestis-gm1259991412-369103055
https://commons.wikimedia.org/wiki/File:Plaguet03.jpg
https://commons.wikimedia.org/wiki/File:Yersinia_pestis_2.jpg
https://commons.wikimedia.org/wiki/File:Flea_infected_with_yersinia_pestis.jpg
[♪ INTRO].

If you were on the internet at all in the past week, you’ve probably heard the name, Dragon Man. That’s the name given to a well-preserved, complete cranium found in China back in the 1930s.

After being hidden for decades, it was rediscovered in 2018, and it became the subject of some pretty astonishing research. And according to three articles published last week in the journal The Innovation,. Dragon Man might represent an entirely new species of human, and possibly our closest evolutionary relative.

Dragon Man’s cranium has space for a big brain, a short, wide face, and small cheekbones. It looks a lot Iike the remains of Homo sapiens from this area that date back to the middle of the Pleistocene epoch, a few hundred thousand years ago. They all have that big skull and wide face.

So researchers had a pretty good idea that Dragon Man lived around the same time. And through different geologic and chemical analyses, they concluded that this guy lived at least 146,000 years ago. At that time, anatomically modern humans had been walking the Earth for about 170,000 years.

But Dragon Man doesn’t quite look like the Homo sapiens that lived back then. For example, his skull is bigger, and its shape is longer and flatter than Homo sapiens’ skulls. These differences made the researchers think that he actually doesn’t belong to our species at all.

Instead, they believe he represents a new species: Homo longi. According to their analysis, modern Homo sapiens and Homo longi shared a common ancestor around 950 thousand years ago. If that’s true, it would make Homo longi more closely related to us than Neanderthals, which we’d thought were our closest evolutionary relatives.

But… not everybody is ready to make this call. Some scientists have commented that Dragon Man seems more likely related to the Denisovans, a group of humans more closely related to Neanderthals than Homo sapiens.

In other words, he might have been around in this timeframe, just on a different evolutionary branch. Either way, Dragon Man tells us that the human evolutionary tree is probably more complex than we realized. But, as always, more research is needed before we totally overwrite our knowledge of human evolution.

Dragon Man wasn’t the only very old and cool thing in the news recently though. Research published earlier this week in the journal Cell Reports documented the earliest known case of plague in human history. While studying the remains of a 5,000-year-old skeleton, scientists found the genetic footprint of a bacterium called Yersinia pestis: the same bacterium that caused the Black Death.

Not only does this discovery push back the record for the earliest plague infection, but it might also give us insight into how the bacteria evolved. The skeleton in question was one of two initially found in modern-day Latvia in the late 1800s, but soon after, they disappeared and were only rediscovered in 2011. Why do old things keep disappearing and being rediscovered?

I don’t know! But after they were rediscovered, scientists revisited the original excavation site, and they found two more skeletons, which were also around 5,000 years old. So the team took samples from all these skeletons’ teeth and bones and analyzed their genomes.

They also checked for evidence of bacteria and viruses to try to learn more about the kinds of pathogens humans were dealing with at that time. And to their surprise, in one of the original skeletons, they found evidence of Yersinia pestis. The bacteria appeared to have been in the subject’s bloodstream, indicating that he had died from the plague, making him the earliest known person to have done so.

But the fact that the plague was around so early on is actually sort of surprising. Most historians think that infectious diseases like the plague evolved in big, densely populated cities where bacteria could easily find new hosts to infect. But this strain of the plague existed way before really big cities were a thing.

In fact, by reconstructing the bacterium’s genome, researchers determined that it came from an ancient strain that emerged about 7,000 years ago, soon after the species evolved. It was pretty similar to the modern-day plague... with one big exception. It was missing the gene that would allow it to hitch a ride on fleas and infect humans.

That gene didn’t evolve until about 1,000 years later. So this unlucky person probably got the plague directly from the bite of an infected rodent. Later on, fleas allowed the disease to spread quickly through human populations, and they were a big factor in making all of the plague epidemics throughout history so deadly.

Today, this all may seem a bit like water under the bridge. But the development of scientific tools, such as the ones that can sequence genomes, has made it possible to study ancient humans, and the pathogens that affected them, in totally new ways. And in doing so, we can learn more about how pathogens like the plague evolved alongside us, and how we evolved alongside them.

Thanks for watching this episode of SciShow! We have made thousands of educational videos over the years, and we’ve been able to offer them for free because of our patrons on Patreon. So, to all of our patrons: thank you for what you do to make SciShow happen.

If you’re not a patron but want to learn more about what that means, and how you can see just long videos of me making a fool of myself, you can go to Patreon.com/SciShow. [♪ OUTRO].