Eons

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 theyd 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 Theyd 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 wasnt just one cradle.

Maybe theyd 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, its messy.

Because were 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 wouldve 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, its 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 wasnt 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, weve 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.

Theyre 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 Lucys great-grandfather and Lucys 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, its 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.