In the early 1920s, a fossil hunting team from the American Museum of Natural History
working in the Gobi Desert was disappointed to report that they’d discovered dinosaur remains.
While most paleontologists would consider this a massive success,
to these researchers, the fossils represented a failure.
Because they hadn't been trying to find dinosaurs at all…
They’d actually been searching for fossils much closer to home
instead - fossils of the earliest humans.
And those dinosaurs only showed that they were looking in the
wrong place and in the wrong geologic time period.
Meanwhile, other people were also hunting for a singular so-called ‘cradle of humankind’
everywhere from Europe, to the islands of Southeast Asia, to imaginary lost continents.
And the reason they were all over the map – literally – was because,
at the time, scientists had no idea where to look for ancient humans.
They just had no clue where humanity had begun.
And it would take decades before they realized that maybe there wasn’t just one cradle.
Maybe they’d been asking the wrong question all along.
Today, humans are pretty much everywhere, on every single continent worldwide.
And this basic fact that we take for granted raises a unique problem.
See, when Charles Darwin published On The Origin of Species in 1859,
he predicted that evolution by natural selection would eventually shed light
on human history and uncover the details of our origins.
But there was no “light” yet – no fossil evidence of human evolution that was widely recognized.
So when it first occurred to scientists to start looking for the fossilized remains
of our ancestors, they had to guess where they should look.
And they had no hints to go on. Other primates,
like chimpanzees and gorillas for example, are found in more restricted areas.
Or, at least, on a single continent: Africa.
So a search for the fossils of their ancestors should probably begin in Africa.
For orangutans, the same would be true for Asia.
But for us, it’s messy. Because we’re everywhere, the question was wide open.
Where did our lineage evolve after diverging from our common
ancestor with chimps – which we now know happened about 6 to 7 million years ago?
Early on, some scientists theorized that our lineage might have originated in Asia.
One German zoologist even hypothesized that humans
had evolved on a now-sunken continent in the Indian Ocean, named Lemuria.
This imaginary place stretched from the south-eastern shores of Africa, toward
India and Indonesia to the east, and would’ve once been connected to land via a land bridge.
It was supposed to have been a tropical “paradise” that would have allowed human ancestors to evolve.
But Darwin disagreed. He thought our origins were located in Africa because
of our similarities to chimpanzees and gorillas.
And in contrast to the paradise idea, some advocates for an African origin argued that,
actually, the harsh environment of South Africa was the catalyst for our ancestors
evolving our human-like features, like big brains.
Environmental challenges and the presence of dangerous predators - not paradise - led to us.
Now, it’s worth noting that there were other perspectives on this topic.
Many cultures around the world had - and still have - their own origin
stories that differ from the ideas of these early western scientists.
And the western scientific debates were often
built on false assumptions about race and superiority - a problematic theme
in the science of human origin that still rears its ugly head even today.
The colonial history of this field of science is why local people in Africa and Asia were
often deliberately prevented from contributing to the research taking place in their own lands.
Instead, they were pushed out by westerners who
centered the debates around their own fossil finds and perspectives.
And, ultimately, those old-timey guys were just speculating.
In fact, Darwin even said it was “useless to speculate,” because a long time had passed
since our origins, giving plenty of time for migrations to happen.
But others speculated anyway.
And by the 1880s, some began acting on those speculations – including a Dutch anatomist,
Eugene Dubois, who traveled to Sumatra and Java to hunt for our origins.
This search resulted in the Java Man fossils, now known as Homo erectus.
And over the next few decades, a series of skulls from the site of Zhoukoudian,
China, found by scientists like Pei Wenzhong, added more evidence for Asia.
But competing discoveries from Africa and even Europe emerging
around the same time left the question wide open.
It wasn’t until the second quarter of the 20th
century that fossils started to accumulate to suggest Africa.
One of the most important of these is a fossil skull of a juvenile hominin
discovered in 1924 in South Africa, dating to around 2.8 million years ago.
Known as the Taung child, the find is among the first early human fossils discovered in Africa,
and it helped the idea of an African origin for our lineage become widely accepted by the 1950s.
Since then, we’ve found many other fossils of potential long lost African relatives dating
to either side of the Taung child on the timeline of human evolution.
For example, now we know about Sahelanthropus, Orrorin, and Ardipithecus.
They’re all very early potential hominins that date to around or shortly after our
divergence from our common ancestor with chimpanzees, some 6 to 7 million years ago.
And around 4 million years ago, the genus Australopithecus appears in Africa, too,
which includes upwards of eight species and encompasses specimens
like the Taung child as well as the famous Lucy.
Many australopithecines have also been found more recently,
including finds nicknamed Lucy’s great-grandfather and Lucy’s baby.
It was this genus that eventually gave rise to our own, Homo, sometime around 2.5 million years ago.
And it was members of that genus, specifically Homo erectus, that seem to have first migrated
out of Africa by about 2 million years ago, eventually spreading to much of Eurasia.
So Darwin, it seems, had been right all along.
But while there's been very little doubt for decades now that our lineage and genus both
emerged in Africa, the question of where our species emerged proved much harder to pin down.
Because, earlier members of our genus made it to Eurasia well before we Homo
sapiens are thought to have first appeared, around 300,000 years ago.
So could a population of hominins have birthed our species,
Homo sapiens, in Eurasia rather than Africa?
This question was wide-open throughout the late 20th century and into the early 21st,
with two competing hypotheses taking center stage…
One was called the Multiregional Hypothesis.
And like the name suggests, the basic idea is that after hominins radiated within and beyond Africa,
different populations in different places regularly came into contact and interbred.
This kept them all very similar by mixing their
various traits into the cocktail that we now know as Homo sapiens.
Which would mean that our species emerged not in one time and place,
but gradually across multiple continents.
In contrast, the Out of Africa model proposed a very different story.
It argued that we can trace our species' origin to a single time and place, somewhere in Africa,
only expanding beyond that continent once we were already fully-fledged Homo sapiens.
The debate over which of these ideas was correct raged for decades,
only really becoming clear in the last 30 years or so.
The genetic evidence showed that we can, indeed,
trace the initial origins of our species to the African continent.
For example, it is now well established that the vast majority of human genetic
diversity today exists in modern African populations.
And this is telling because it suggests that people who are not
African are descended from only a small group of people who left the continent,
taking just a fraction of the total human gene pool with them.
Scientists call this a population bottleneck.
So, in some ways, the Out of Africa hypothesis was correct.
But the genetic evidence also shows that, when ancient Homo sapiens left Africa,
they interbred with our cousins the Neandertals and Denisovans in Eurasia.
And because the Out of Africa hypothesis originally argued
that Homo sapiens replaced other populations rather than interbred
with them, this means aspects of the multiregional model were right, too.
To make things more interesting, it turns out that the Out of Africa migration around
60-to-80 thousand years ago was just one of many – though it was the only one that
clearly left direct descendants, who are still all over the world.
But even knowing that Homo sapiens are from Africa,
we are still left with at least one big question…
If the cradle of humankind was indeed in Africa, where exactly on the continent was it?
After all, it’s a vast and ecologically diverse continent - spanning thousands of
miles and containing everything from deserts to savannas to rainforests.
So where exactly is our childhood home?
Well, in just the last few years,
scientists have begun to realize that this may be the wrong question altogether.
Because a series of recent studies using DNA from both modern and ancient people,
as well as archeological and environmental evidence,
have begun to paint a much more complex picture of our African origins.
One where we didn't actually evolve in one single population in one single place…
Instead, we can trace our emergence to multiple ancient
populations that were scattered across Africa.
When environmental conditions allowed, they occasionally met up and mixed their genes,
all contributing directly to the eventual rise of us ‘modern’ humans, some 300,000 years ago.
There was no single cradle, it was a continent-wide playpen!
And instead of thinking about our origins like a tree with a single trunk,
perhaps the more accurate view is a complex braided stream…
An intertwined story of migrations, transitions, and exchanges between
various ancient populations that unfolded over vast time and space.
No human is an island, and it turns out that this has been the case since our very earliest days.
Our friends over at Crash Course have launched a podcast!
And if you thought we looked into the ancient past,
wait until you listen to what they have in store.
The Universe is a new limited series podcast from Crash Course where Dr. Katie Mack,
a theoretical astrophysicist, walks John Green through the history of
the entire universe - including the parts that haven’t been written yet.
Join John and Katie as they discuss the Big Bang,
cosmic dawn, black holes, and, eventually, the end of our universe.
It’s available now on the Crash Course YouTube channel and wherever podcasts are available!
Now our closest relatives, the Neandertals, lived in Eurasia for more than 300,000 years.
They were expert toolmakers, skilled hunters and foragers, and may even have created cave art.
So what caused the disappearance of their population?
Well, in a way...it could’ve been us. But maybe not in the way you might’ve heard.
Check out our episode, “Why the Paleo Diet Couldn’t Save the Neandertals” to learn more.
And thanks this month’s modern Eontologists!
Jake Hart, Raphael Haase, Annie & Eric Higgins, John Davison Ng,
Melanie Lam Carnevale, Addie, Tony Dai, and Juan M.
You can become an Eonite and help us make the show at patreon.com/eons.
And as always thank you for joining me in the Adam Lowe studio. Subscribe at
youtube.com/eons for more evolutionary escapades.
When environmental conditions allowed, they occasionally mate- met up...
and mixed their genes -
What a creative way...
to say "doin' it".
[laughs]