It’s 1912, and an amateur archaeologist
named Charles Dawson came forward with a discovery that almost changed our understanding of human
evolution. Almost. Dawson’s find was some unusual human-like
skull fragments, and he showed them to the Keeper of Geology at the British Museum, Sir
Arthur Smith Woodward. He explained that the fragments were given
to him by some gravel quarry workers near the town of Piltdown in England a few years
earlier. So the two men returned to the site and find
some additional animal fossils that provided an estimated age for the skull bones: Early
Pleistocene, making it the oldest evidence of a human ancestor ever found. The excitement then continued with the discovery
of a lower jaw that seemed to match the skull. But it’s teeth were odd; the molars showed
patterns of wear that were similar to those found in humans. And a canine discovered later at the same
site was intermediate in size between ape and human canines. With its large cranial capacity -- close to
that of modern humans’ -- Dawson’s fossil closely matched what experts thought a human
ancestor was supposed to look like at the time. It was named Eoanthropus dawsoni and was hailed
as a “missing link” in our family tree. And this fossil was also … fake. Totally made up. What’s known today as the Piltdown Man hoax
is probably the most famous evidence you’ll ever find that, even in science, bad ideas
take a long time to die. In this case, the idea was that of the Missing
Link -- the idea that somewhere out there, there had to be some hypothetical specimen
that would partly resemble an ape but also partly resemble a modern human. But, there is no missing link in our lineage,
because that’s not how evolution works. And the fact is, the search for the Missing
Link was just one phase in the evolution of our thinking about … human evolution. The idea of a “Missing Link” has fascinated
people for as long as we’ve been studying our origins. But most scientists today don’t use that
term to talk about the fossil record, because evolution is a lot more complicated -- and
way weirder -- than just a series of species lined up single-file. So, the changing ideas about the existence
of a “Missing Link” are closely tied to how the prevailing thinking about evolutionary
theory in general has changed. The oldest model for thinking about change
over time was known as orthogenesis, which presents a linear model of evolution, with
species progressing from one form into the next toward some kind of goal or ideal. And in the early 19th century, evolution was
thought to be linear, based on the premise that species evolve from other species, and
that forms between the two should have physical traits that resemble both the older and the
younger forms. Linear evolution is usually depicted as the
so-called March of Progress, an image that’s still very popular today. And the idea of linear evolution made it easy
to accept the Piltdown Man as a ‘Missing Link,’ because it reflected that logic:
It was a creature that was halfway between a human and other great apes. But the PiltdownMan hoax overshadowed the real, legitimate
fossil discoveries that were being made around the same time, all over the world. For instance, there was Java Man found in
Indonesia in 1891, and Peking Man discovered in the 1920s in China, both specimens
of Homo erectus. These finds were largely overlooked, because
they didn’t fit another bad idea of the time --- namely, that the first modern human
feature to evolve was our large brain. Compared to the so-called Piltdown Man, Java
Man and Peking Man had small brains and smaller, human-like canines. And not only were these Asian discoveries
dismissed, but Africa was also left unexplored in the search for human origins. The reasons for this had more to do with social
politics than science, including the widespread bias against the notion that the first humans
were Africans. But in 1924, while Piltdown Man was still
enjoying considerable fame, limestone workers in the town of Taung, South Africa discovered
a fossil that they presented to anatomist Raymond Dart. It was the tiny partial skull and endocast
of a juvenile primate, which Dart called the Taung Child. He eventually gave it the scientific name
Australopithecus africanus, the southern ape from Africa. And for a while, Dart himself wondered whether
this child represented a missing link. But the evidence he found flew in the face
of conventional wisdom. It was clear from the fossil that the Taung
Child had a small brain, and human-like teeth -- the exact opposite of Piltdown Man. The discovery was widely criticized among
European researchers -- including, unsurprisingly, the supporters of the Piltdown Man hoax. But the Taung Child’s strange combination
of features, along with those other finds from Asia, convinced some prominent anthropologists
that maybe our evolution wasn’t as linear as they’d thought. Adding to the debate, major doubt was cast
on Piltdown Man in the 1930s when a geologist mapped the gravel around the site and closely
correlated it to the River Thames deposits. So how could an ancient hominin be buried
in modern sediment? Finally, in the 1950s, Piltdown Man was, at
long last, debunked as a fraud. Fluorine tests, and later, carbon dating revealed
that the fossils weren’t from the Early Pleistocene -- they were more like 600 years
old. And the jaw probably came from an orangutan
whose teeth had been filed to look like it was part-way between an ape and a human. Using microscopes, researchers revealed miniscule
scratches left behind by the file on the unnaturally flattened molars. The Missing Link was never missing; it turns
out, it had never existed at all. As more fossil discoveries were made throughout
Africa in the mid 20th century, the linear model of evolution was abandoned. Instead, these finds gave rise to a new way
of thinking: phylogeny, which depicts evolutionary relationships as branching trees. This Branching Tree model took a slightly
more complicated approach to human evolution, acknowledging that not every fossil discovered
was directly ancestral to us. Also that ancestor and descendent species
could overlap in time. Additionally, this model demonstrated that
there were many branches off the main trunk, resulting in ‘evolutionary dead ends’
-- species that went extinct without leaving any modern descendants. These side branches included sister taxa like
the Paranthropines from East and South Africa. Who were robust hominins with large teeth
and wide faces that did not fit the criteria to be our ancestors. So the Branching Tree model was an improvement
over the old March of Progress. And for a while, we thought it was what human
evolution looked like. But then at the turn of the 21st century,
new technology for sequencing ancient DNA - like from Neanderthals and Denisovans - came
along. And new fossil species were discovered that
lived at the same time, like Australopithecus sediba, which overlapped in time with Homo
habilis. These developments revealed that our family
tree was a lot more complicated than just a branching tree or bush...and that it was
time to update our model. It’s now called the “Braided Stream”,
a new way of thinking about human evolution that takes into account our interbreeding
with other hominin species. The Braided Stream is something that biologists
and geneticists have seen in animals for years, but it has only recently been applied to humans. It depicts evolution as a series of channels
that sometimes branch off each other, but also sometimes reunite at various points. And as different lineages shared genes, it
resulted in hybridization. This model captures crucial information that
was missing from the Branching Tree model: It shows how species can reconnect after their
initial split from a common ancestor. And it highlights the importance of gene flow
in our evolution as a species. So instead of searching for missing links
in the fossil record, the search has begun instead for fossils that show evidence of
gene flow, physical proof of what we know from our DNA, that all of us are a product
of interbreeding. And even before DNA sequencing, some researchers
used experimental studies to figure out what hominin hybrids might have looked like, and
to determine if we may have already found some in the fossil record. Experimental models on baboons, for example,
have shown that hybrids tend to be larger than either of their parents, and they tend
to have large teeth and extra bone-joints, called sutures, in their skulls. So based on studies like these, researchers
think we have already found fossil human hybrids! A jawbone found in Romania dating back some
40,000 years, for example, has been found to have had both Human and Neanderthal ancestry. Experts could tell this not only because of
variations in its teeth and jaw, but it was later confirmed with its DNA, which showed
that the hominin had a recent Neanderthal ancestor four to six generations back. So, the Braided Stream model accounts for
the fact that some hominins didn’t view other types of hominins as that different. And because of our close evolutionary relationships,
we were able to reproduce with them and carry our combined genes into the next generation. The evolution of evolutionary thinking has
gone from a simple linear model to an increasingly complex branching tree and now a braided stream. And the more complex we realize that our evolution
has been, the more remarkable it seems! It’s the product of multiple populations,
over millions of years, existing together, and exchanging genetic material. It aided our process of adaptation that allowed
us to thrive in a range of environments all over the world. Through the combination of DNA studies, fossil
discoveries, and experimental data on hybridization, we’re still trying to create the most complete
depiction possible of our human family. And now we can all stop looking for -- or
inventing fake versions of -- a ‘Missing Link,’ because we know that a fossil that
is ‘half human and half ape’ simply does not exist. It’s taken a hundred years and many changes
in our thinking, but we’ve come a long way from Piltdown, the greatest hoax ever to rock the
world of human origins - the missing link that wasn’t. Thanks to this month’s Eontologists: Patrick
Seifert, Jake Hart, Jon Davison Ng, and Steve. If you’d like to join them and our other
patrons in supporting what we do here, then go to patreon.com/eons and make your pledge! And also thank YOU for joining me today, in
the Konstantin Haase Studio. If you want more adventures in deep time,
just go to youtube.com/eons and subscribe.
Thanks