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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
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