Imagine the scene
it was 1871
and Charles Darwin had just suggested
that we humans did not in fact walk
fully formed, out of the primordial sludge at the beginning of time
instead, in his book "The Descent of Man",
He proposed that humans descended from African apes.
Naturally, his Victorian contemporaries were all
"Ooooo... Fetch me my smelling salts..." and clutching at their pearls
and what not
and maybe you can't blame them for being shocked because Darwin's idea
is still shocking people
like a 140 years later.
But, as he often was, Darwin was right.
The amazing thing was that he proposed his theory of human evolution
when there was almost no fossil evidence
of any other kinds of Hominins
That includes us and our ape-like ancestors on Earth.
It took another 50 years for enough fossils to pile up
to start corroborating Darwin's Theory,
and another several decades to piece together
compare and argue about how these species related to each other.
Actually, that is a process that is still going on right now.
These days about two dozen Hominid species or possible species
have been identified, and while the Hominid family tree
looks sorta like a prickly bush at the moment,
taken together these fossils do show us
how our ape-like ancestors evolved into modern human awesomeness.
See, on the journey from the genus Australopithecus
to the genus Homo, our ancestors reached
a series of game changing evolutionary benchmarks.
Whether they were acquired traits or new behaviours,
that gave its species a huge advantage over the previous ones.
We exist largely because of those evolutionary breakthroughs
So, what are they?
And who else is in our family bush?
And will this be on the final?
Follow me into the facts of human evolution.
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Our understanding of where we came from
has changed dramatically in just the last 50 years.
If you were a paleoanthropologist working in the 1970's,
you'd probably believe that there was a bunch
of different human species running around on Earth
for millions of years, and that they all sorta interbred
when they bumped into each other.
This is known as the 'Multiregional Hypothesis'
and it suggested that Neanderthals in Europe,
for example evolved into Modern Europeans.
While Homo Erectus in China would have been the predecessor
of Modern Asians,
and that Java Man found in Indonesia
would have been the ancestor
to Australian Aboriginal Peoples.
These days Multiregionalism has fallen out of favor,
mostly because in the 1980's researchers started
studying mitochondrial DNA.
That's the ancient DNA found in the mitochondria of our cells,
which is totally separate from the DNA in our cell's nuclei,
that's the stuff that we inherit from both our parents.
Mitochondrial DNA, on the other hand, is passed down
only from the mothers to their offspring
and by following its various mutations over time
and across populations, scientists have been able
to track the migration of humans over the past 200,000 years.
All the way back to a single ancestral population
of modern humans in Africa.
This genetic evidence combined with the fact that
all of the oldest Hominin fossils have come from Africa,
led to the Out of Africa Hypothesis
which suggests that anatomically modern humans
evolved exclusively in Africa
and then spread across the world in 2 different waves.
One wave which happened anywhere from 70,000 to 125,000 years ago
took a right-hand-turn out of Africa, populating the Middle East, Asia, Indonesia, and Australia.
The second wave happened much later and headed straight up through Europe.
So that's currently the most popular idea about where we came from
but when it comes to how hominins evolved,
there are only a few thing we're sure about.
For starters, there did used to be a lot of different species of people running around
and now there's only one.
And thought we share the vast majority of our DNA with chimps
Our common ancestor with them probably lived about 7 million years ago, maybe more
It was about a million years after that break with chimps
that the Homo Sapiens saga really began when a segment of an ancient population of apes
acquired the first real breakthrough in human evolution, bipedalism.
This is when apes somewhat obviously started walking upright and on two feet
And there were a couple of different, early, semi-bipedal genera of apes
And these probably evolved into the australopithecines
Who we can call grandma and grandpa.
Australopithecines weren't that different from other ancient African apes
They were about the same size and they had the same size brains
In fact, the first australopithecines like Lucy, the 3.2 million year old australopithecus aferensis fossil
found in Ethiopia in 1974, was probably about a meter tall
and didn't look too different from a modern chimp.
But we know that Lucy walked upright due to the shape of her bones
and because we found fossilized footprints of her buddies.
And though there are a few different theories about why bipedalism may have evolved
it seems to have happened just as the dense African forests were shrinking due to climate change.
So early hominins may have been forced out onto the grasslands where bipedalism
made it easier to spot predators, to travel long distances,
and to pick fruit off trees.
But bipedalism was most important because it freed up two of our limbs.
When you got two hands just hanging out not doing anything
the next obvious step is to pick up a rock and start smashing stuff.
And voilà
You got an ape... using a tool
And this led to the second major characteristic to advance human evolution, a precision grip.
As hominins evolved, they used their hands more and more for gripping and manipulating small objects
than swinging through trees and what have you.
So over time, the big curved hands that we associate with chimps and gorillas
were replaced with smaller, more nimble hands with powerful thumbs
that you can see at the end of your arms right now.
These hands were better suited for using slicing tools and our first tool making ancestor
may have been Homo Habilis, aka handy man
Homo Habilis was the first obviously human-like hominin in the fossil record
and he's thought to be the earliest member of the Homo genus.
He first appeared about 2.4 million years ago and was probably the direct descendant of the australopithecines.
I have to say probably because, you know, I wasn't there and there will always be holes in the fossil record.
And Homo Habilis probably couldn't have fixed your dish washer but he could totally have smashed it to pieces
with a rock.
In addition to acquiring more dexterous hands, Homo Habilis ate meat.
Its omnivorous diet was a new thing for previously vegetarian hominins
and it turned out to be another game changer for the genus Homo
because it kick-started the process of encephalization.
Or the growth of the brain in relation to the overall body mass.
See building and maintaining brains requires a ton of calories,
so even though the first omnivorous hominins were probably scavenging gazelle scraps from saber tooth cats or something
Meat was a big enough part of their diet that their brain size increased pretty rapidly.
Some argue that Homo Habilis was also probably the first human ancestor to figure out how to cook food.
Cooking unlocks all sorts of calories and nutrients from vegetables and tubers
as well as making rotten, scavenged meat less dangerous.
So overall nutrition for these guys improved a LOT around this time,
and brains as a result got bigger.
But it wasn't just brain size that evolved, the pattern of brain growth was really important too.
Over time, our ancestors temporal lobes which house the centers for language processing
and the prefontal cortices which help with complex decision making and moderating social behavior
grew disproportionately to the other parts of their brain.
Some researchers think this had a lot to do with the vastly improved diet
and at the same time a need to solve social problems which was becoming more and more important.
One reason for this can be found in the fossils of Homo Ergaster
Which came on the scene about 1.65 million years ago
A lot of people think it's the desendent og Homo Habilis
They looked even more like modern humans than Homo Habilis
They had smaller jaws, and sharper teeth, and were taller and more slender.
They were also probably the first mostly hairless hominins
But one very interesting detail is that Homo Ergaster had hips so narrow as to make the unassisted delivery
of a baby very difficult. And since Ergaster had bigger brains, their babies had to have probably also
considerably larger than those of past hominin babies.
So, baby heads were getting bigger as females pelvises were getting smaller.
The only solution was for babies to be born before their brains were fully formed
so that they could pass through the birth canal.
But this meant that after birth, babies were less developed, requiring more care than ever
and for a longer time.
This required Ergaster and later members of the Homo genus to develop another breakthrough
That could only be possible with big sophisticated brains.
I'm talking, of course, about complex social behavior.
More so than anyone who came before them members of Homo Ergaster really needed each other.
For delivering each other's babies, for caring babies that took freaking forever to mature
For finding enough food to sustain everybody, and for hunting, which Ergaster probably did in groups.
It's also possible that Homo Ergaster was the first human to leave Africa
Maybe in search of better hunting grounds
Ergaster bones dated to around 1.75 million years ago and have been found around the border of Armenia and Georgia.
Shortly afterward we start seeing the genus Homo Erectus
The first early human whose fossils have been found in large numbers outside of Africa
And it seems like they did really well for themselves
Homo Erectus, was kind of my favorite grandpa.
Or maybe great uncle. Nobody's sure.
Because during the heyday of Homo Erectus, about 400,000 to 600,000 year ago
we begin to see another species of hominin.
Homo Heidelbegensis which some believe to be the direct descendant of Homo Ergaster
Since they were very similar with a couple of exceptions.
For instance, some scientists believe that Heidelbegensis was the first hominin species to bury their dead
But possibly the most important thing about Homo Heidelbegensis is that many believe
It's the direct predecessor to modern Homo Sapiens.
And possibly, also to our thick-browed cousins the Neanderthals, aka Homo Sapiens Neanderthalensis
Or Homo Neanderthalensis.
One theory is that a population of Heidelbergensis remained in Africa
and modern humans descended from them, while other Heidelbergensis hoofed it up through Europe
and Neanderthals derived from that group.
This, like many other things in human evolution is hotly contested.
What we do know is that
And though they had pronounced brow ridges and were heavier set than we are
They look pretty similar to modern humans
Their brains seem to have been a little bit larger than ours,
and modern humans and neanderthals apparently shared some cultural habits,
like burying our dead, making art,
and using tools to beat the crap out of each other.
And of course, they totally found some time to get it on with each other
we've been able to reconstruct almost the entire neanderthal genome
and it turns out, that about 2.5% of our DNA is from some neanderthals who - I guess -
some of our great-great-great...-great-grandmothers
spend a great night within a cave in Israel!
So that brings us up through modern humans, but the story of our ancestry
is always changing, because exciting discoveries are being made all the time.
For instance, in 2004 researchers found fossils of Homo Floresiensis
a.k.a. the Hobbit, a tiny person that lived about until 13'000 years ago
in what is now Indonesia. Even more recently,
in 2008, fossils of a new people, the Denisovans, or Denisova Hominin
were discovered, researchers think may have overlapped, and possible, interbred with modern humans,
and the discovery of Australopithecus Sediba, also in 2008,
has some paleo-anthropaleologists in a dither about whether it could be the real
direct progenitor for the genus homo, and also the first tool maker.
So, it's an exciting time to be researching our origins.
No one's really sure what killed off these other species, some theories suggest
it was climate change, or a catastrophic event like a supervolcano eruption,
or simply not being able to compete with [points fingers] This.
Maybe we are the survivors because of our big brains,
we had to evolve to help each other out,
and because we eventually developed agriculture about 10'000 years ago,
which caused a huge population explosion
that is still going on today. But now,
it's just us. Which makes me a little bit sad.
It's pretty strange to think that if we went back in time just a 100'000 years,
like yesterday afternoon, geologically speaking,
we'd be sharing the earth with 6 different kinds of humans.
Somethin' tells me that playing Mario Party with a neanderthal would be like
would be like a dozen different kinds of awesome, but
I guess I'll never know.
Thank you for watching this exceptionally long SciShow infusion
couldn't help it, there was a lot to cover
If you have any questions / ideas, please leave them down below in the comments
or on Facebook and Twitter, and we'll see you next time.
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