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  • Hi, it's Hank with news about some new benefits for our Patreon Patrons!

  • People pledging $15 or more now have access to a quarterly livestream with the Eons team!

  • And if you pledge $100 a month, you can actually take part in the actual video stream and nerd

  • out with us face to face!

  • Sound fun?

  • You can go to patreon.com/eons to find out more

  • But now, let's talk about some planetary domination.

  • Today, our species - Homo sapiens - lives on every continent on Earth.

  • There are more than seven billion of us, inhabiting almost every possible environment, and altering

  • them through our use of culture and technology to suit our needs.

  • We can survive harsh winters, irrigate deserts, and travel at will to reach the most remote

  • islands.

  • But we weren't always so widespread.

  • One of the defining features of our species is that we're behaviorally flexible.

  • We can use whatever resources are around in order to survive.

  • We've been like this for a long time, and it's a big part of the story of our success.

  • The early ancestors that we call the first anatomically modern humans were more like

  • us than any other member of the genus Homo, with more slender skeletons; smaller, less

  • protruding jaws and teeth; and really big brains.

  • These ancestors had to be able to adapt to all kinds of new environments as they spread

  • around the world.

  • And adapt they did.

  • They encountered other hominin species, faced new predators and diseases, and found the

  • food and shelter they needed to thrive in new landscapes.

  • And we can actually trace the path they took, from our deepest origins in Africa all the

  • way to the Americas, by looking at the fossils and archaeological materials they left behind,

  • as well as in the genomes of their descendants: our genomes.

  • Now, we don't know all the details of this journey, but we can say for sure that it was

  • an epic one.

  • In the last 300,000 years or so, we've gone from inhabiting a single continent to all

  • of them.

  • Our story as a species is one of constant migration.

  • So, no discussion of human evolution would be complete without a deep look through that

  • short window of time when we took over the world.

  • Based on our current understanding of the evidence, the story of Homo sapiens begins

  • in Africa, between 300,000 and 350,000 years ago.

  • In 1961, miners working at a site called Jebel Irhoud in Morocco accidentally unearthed the

  • fossil remains of a hominin with facial features that were surprisingly like those of modern

  • humans.

  • But at the time, the remains couldn't be dated precisely.

  • And in the last few years, anthropologists have gone back to that site and found even

  • more fossils - including another skull.

  • This new one had the same mix of modern facial features, like smaller brow ridges, and also

  • more basal traits, like a braincase that was longer and lower than the ones we have today.

  • And researchers were able to date these new finds to between 300,000 and 350,000 years

  • ago - a surprisingly early date for hominins with such modern-looking faces.

  • Before that find was made, the oldest known remains of modern humans were skulls from

  • two sites in Ethiopia, dated to 195,000 and 160,000 years ago, respectively -- more than

  • 100,000 years younger than the material from Jebel Irhoud.

  • And while these younger skulls share some features with us -- like the same shape and

  • size of their braincase -- they've still got some fairly robust features, too -- like

  • heavy brow ridges -- which we associate with more archaic hominins.

  • So we've got fossil evidence of early Homo sapiens from northern and eastern Africa.

  • But the evidence in our genes paints a slightly more complicated picture.

  • Our genomes can be used to infer the history of our migrations, by comparing the DNA from

  • human populations in different places, and seeing how they differ.

  • Variations in our genomes are generally thought to correspond to how far apart certain populations

  • have been separated, in both distance and time.

  • Groups that live closer to each other are expected to be more similar, while groups

  • living farther apart are expected to be more different.

  • And older, more ancestral lineages typically have more genetic diversity than newer ones.

  • So based on the DNA we've studied of living peoples, there's evidence for modern human

  • origins all over Africa, not just the north and the east.

  • African populations turn out to have the greatest genetic diversity of any group of people in

  • the world.

  • So this suggests that their lineages are older.

  • Meanwhile, all of the populations outside of Africa have just a fraction of the diversity

  • found in Africa, suggesting that their variations are more recent.

  • But the pattern of genetic variation found within populations in sub-Saharan Africa points

  • to a complicated history of migration, genetic exchange, and selection.

  • And in the end, that makes it impossible to pinpoint a single place in Africa as the origin

  • of modern humans.

  • In any case, we do know that, after arising in Africa, some groups of Homo sapiens started

  • to spread to other continents.

  • Anthropologists usually draw these migrations as one-way arrows on a map, but that oversimplifies

  • what was likely a more complex process.

  • Some populations expanded but then contracted again, and some moved back and forth between

  • populations in various places.

  • So we're not sure who the first modern humans were to leave Africa,

  • or even how many times they made the journey.

  • We also have questions about what route these migrants took: Some fossil evidence suggests

  • that they went north, through that region of the eastern Mediterranean known as the

  • Levant, about 100,000 years ago.

  • But there's genomic evidence of a possible southern route, which might have gone from

  • Ethiopia into the southern part of the Arabian peninsula and from there into Asia and Oceania.

  • If we follow the northern route first, we find fossil evidence at two sites in what's

  • now Israel.

  • One of them is called Misliya Cave.

  • In 2018, anthropologists published their discovery of half of an upper jaw with teeth that are

  • unmistakably human, along with evidence of hearths and well-developed stone tool technology.

  • Dated between 177,000 and 194,000 years ago, this site is considered by many to be the

  • earliest known evidence of modern humans outside of Africa.

  • Another site, called Skhūl, is part of the same complex as Misliya Cave, but it's more

  • recent, dated to 100,000 to 135,000 years ago.

  • Excavated in the early 1930s, it has yielded the remains of at least 10 adults, some of

  • which appeared to have been intentionally buried, providing early evidence of modern

  • human behavior.

  • Even further across the globe, there are two sites in southern China with modern humans

  • that overlap in time with those at Skhul.

  • And we don't know how these populations got there -- like, whether they came from

  • the Levant or by that southern route into the Arabian peninsula.

  • One site is known as Luna Cave in the region known as Guangxi.

  • It has produced just two teeth, only one of which could be definitely assigned to Homo

  • sapiens, and both were dated to between 70,000 and 127,000 thousand years ago.

  • The other site is Fuyan Cave in Hunan Province, and it has yielded 47 teeth, all from modern

  • humans, and they've been dated to between 80,000 to 120,000 years ago.

  • Teeth: They last!

  • But what happened when our ancestors made it to the edges of mainland Asia?

  • Well, the only way to go from there seemed to be across open water, which would've

  • presented its own challenges.

  • Sea levels did vary in the Pleistocene Epoch, and probably made some crossings a little

  • easier, but our ancestors still would've had to find a way to get to the islands of

  • Southeast Asia.

  • And we don't know how they did it, but we know they got there.

  • On the island of Sumatra in Indonesia there's a cave site called Lida Ajer, where modern

  • human teeth have been found.

  • They've been dated to between 63,000 and 73,000 years ago, and they represent the earliest

  • known occupation of a rainforest by modern humans, again demonstrating our ability to

  • adapt.

  • And from these islands, our ancestors continued on through Oceania to Australia.

  • Archaeological evidence suggests that anatomically modern humans reached northern Australia between

  • 50,000 and 60,000 years ago, leaving behind stone tools and animal remains at a site called

  • Madjedbebe.

  • And for a while, that was the southernmost extent of our species' reach.

  • But what was happening to the north?

  • What happened to the populations that dispersed into the Levant and then turned northwest

  • instead of southeast?

  • Well, the first modern humans that showed up in Europe at two different sites at around the same

  • time, about 43,000 years ago.

  • We've found their teeth, of course, at a site in southern Italy called Grotta del Cavallo and a jaw

  • fragment from a site known as Kent's Cavern in the UK.

  • But these sites are more than 2000 kilometers apart.

  • So, when it comes to how and when the rest of Central Europe was settled, we're missing

  • a lot of evidence.

  • The rest of the human journey starts in Siberia, with some seriously adventurous populations

  • that crossed the Bering land bridge into North America.

  • Again, based on genomic data, it seems likely the native peoples of the Americas made their

  • move between continents around 16,000 years ago.

  • Humans become much more widespread in North America between 12,600 and 13,000 years ago,

  • with the rise of the Clovis complex, a type of stone tool technology that's found

  • across North America but isn't necessarily associated with any one group of people.

  • Remains that have been found with these distinctive tools have shown that members of this complex

  • were the ancestors of many Native American peoples today.

  • And the same kind of expansion was occurring in South America around the same time.

  • The earliest site on that continent is the Monte Verde site in Chile, dated to 14,500

  • years ago.

  • It preserves the remains of hearths, and tools and artifacts made of reed, bone, and stone.

  • No teeth though

  • The fact that people appeared at the southern tip of the Americas so long ago suggests that

  • humans might have quickly migrated south along the Pacific coast, almost as soon as the peopling

  • of the continents was possible.

  • And that's the whirlwind tour of our global journey as a species.

  • Homo sapiens arises as a species in Africa, maybe as early as 300,000 years ago.

  • The earliest fossils of modern humans outside of Africa come from caves in Israel, dated

  • to between 177,000 and 194,000 years ago.

  • Some members of our species make it across much of mainland Asia to southern China around

  • 100,000 years ago, give or take 20,000 years.

  • From there, they venture to Australia between 50,000 and 60,000 years ago.

  • And they're also found at two sites in Europe around 43,000 years ago.

  • The last continents to be reached were North and South America, starting around 16,000

  • years ago.

  • We've covered a tremendous amount of ground in a short time, geologically speaking.

  • But our origin is on the African continent, and it remains central to our story as a species

  • and as a genus.

  • Our greatest genomic diversity as a species, to this day, is there.

  • And as genomic techniques improve and as more exploration and excavation becomes possible,

  • we're learning more and more about how and when we expanded across the world.

  • Plus, we know we weren't alone on this global journey.

  • We encountered and interbred with archaic hominin populations within and outside of

  • Africa along the way.

  • But that's a story for another time.

  • Today's episode was recorded in the Konstantin Haase studio.

  • Thanks to Konstantin and this month's Eontologists: Jake

  • Hart, Jon Ivy, John Davison Ng, and Steve.

  • for their support on Patreon

  • Thanks for joining us here on Eons

  • if you want a whole new show to fall in love with, then you MUST check out Monstrum,

  • a new show from PBS Digital Studios that explores monsters and myths from cultures around the

  • world.

  • Don't be afraid!

  • It's only monsters!

Hi, it's Hank with news about some new benefits for our Patreon Patrons!

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When We Took Over the World

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    joey joey に公開 2021 年 05 月 02 日
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