So today we're going to talk about human evolution. Evolution is this really powerful idea in biology
that helps us understand how all living things are related to one another. And when we understand our own evolution,
it helps us see how we're connected to other living species on the planet today.
So humans are a member of the order primates, which is the mammals that include
apes, monkeys, lemurs, and lorises. Now we can tell we're primates because if we look at our fingers,
we see nails rather than claws, our eyes face forward, right?
So we have primate characters that we share with any other primate alive today
monkeys, apes and lorises, for example.
Within the primates were a member of the ape group.
And so apes include chimpanzees like the skull here, bonobos, gorillas, orangutans and gibbons.
And we can tell that we're apes because the way our bodies are shaped today.
So our shoulders for example, stick out to the side, and our arms can reach up above our heads
just like our ape relatives can when they're hanging from branches in the trees.
We don't have tails, just like none of the other apes have tails.
And of course, our DNA is over 98% similar to living apes today.
So humans are primates, within primates, we're apes.
And within the apes, we're most closely related to chimpanzees and bonobos.
So the chimpanzee and bonobo lineage and our lineage split about 7 million years ago in Africa.
And when we talk about human evolution, we're often talking about that 7 million year lineage
of our evolution after we split from chimps and bonobos.
And that 7 million year history of our lineage I like to think of it in terms of three chapters:
the earliest hominins, the middle chapter, which belongs to the genus Australopithecus
and then the last chapter, which is our chapter, the genus Homo
Now, the earliest hominins are represented by species like this, Ardipithecus,
which is an four and a half million years old and was found in Ethiopia.
All the earliest hominins are found in Africa. And you notice right away when you look at a species like
Ardipithecus that is quite ape like. And that makes sense because the farther back we go in our evolution
the more we look like our ape-like ancestors.
But notice here when we look at Ardipithecus that the brain size is very similar to chimpanzees.
The face pushes forward is projects like ape faces do, it's not pushed in like our face is.
And if we look at the way that the species uses landscape, we know it was up in the trees a lot.
In fact, it had a grasping foot. So here we have two left feet.
This is a modern human foot, like mine, and this is the left foot of Ardipithecus, one of those earliest hominins.
And as you can see, in the modern human foot, the big toe is in line with all the other toes.
But in the earliest hominins, that big toe stuck out
and so it almost more like a hand that could have grasped branches as it climbed.
So we know that species like Ardipithecus, that first chapter of our evolution
was very ape like and the way they use our environment.
Now there are two things that separate these earliest hominins from other apes, and help us know
that they're in our lineage and not some other ape lineage.
And that is the way they walked. And the way their canine teeth are shaped.
So these earliest hominins walked on two legs like you and I do like all hominins did.
And we know that because we have fossils from the pelvis and the feet and lower limbs,
but also because we can even see evidence for this in the skull.
So if we look at the foramen magnum
(that's the hole in the bottom of your skull where your spinal cord comes out)
It's pushed forward in its early hominins, like Ardipithecus.
And that's because when you walk on two legs, your spinal column comes straight down out of your head.
So if I turn to the side like this, you can see that my spinal column is coming straight down out of my head.
Because I spend my life, like you do, upright.
The chimpanzee, the foraman magnum, the hole for the spinal column
projects more backwards, more horizontally out of the back of their head
because they spend their lives on all fours.
So we can see that bipedal, that two legged walking, even in the skull of these earliest hominins.
The other thing we notice about these earliest hominins is that their canine teeth are small.
So if we look at the male chimpanzee skull here, it's canine is huge. And that's typical of apes.
The males have these really big canines that they use to fight each other for
access to females. So the fact that we see small canines, like our canines are small
We see those small canines in the earliest hominins tells us
that they're organizing their social world in a different way than other apes do.
That's chapter one, the earliest hominins.
Chapter two is dominated by this genus called Australopithecus.
And the most famous member of Australopithecus is Australopithecus afarensis
which is what the famous Lucy skeleton is a member of.
So here's a skull of Australopithecus africanus.
Not Lucy species, but a sister species.
Like Chapter One, all of chapter two takes place in Africa.
And so you can see with with Australopithecus here.
We still have a relatively ape like head, the face still still projects forward.
The brain size is a little bigger, but not much
So in terms of intelligence, cognitive abilities, probably similar to apes living today.
One thing that we see that changes in this middle chapter
with Lucy and other Australopithecus species is
the lower limbs are much more like ours are today.
So the pelvis looks much more like a human pelvis,
the foot looks more like modern human foot with a big toe in line with the other toes.
So from the waist down, they look a lot more like we do
compared to earlier members of our lineage.
However, they're still very ape like in the way that they're making a living.
So they're still eating an almost entirely plant based diet.
There's still up in the trees, probably to get food and maybe to sleep at night.
And like I said, brain size, overall head shape, still quite ape like.
The one distinctive thing about Lucy and other Australopithecus is that the teeth are quite big.
the molars, those cheek teeth that we use to chew our food with
in this species are much larger than earlier hominins and in fact, even larger than ours.
and that suggests that not only it wasn't a plant based diet for Australopithecus, in this middle chapter.
But probably the foods are more fibrous, tougher, harder to chew.
So chapter three starts about two and a half million years ago.
And this is the chapter that's our genus, the genus Homo.
And the big thing that changes that gets everything else started with our chapter
is the way that we get our food. It's the beginning of hunting and gathering.
So if we look at Australopithecus or earlier hominins, or even living apes today,
we see they're eating almost entirely a plant based diet.
Chimpanzee will sometimes hunt but it's almost all plant foods in their diet.
What we see about two and a half million years ago, is the use of stone tools,
and probably cooperative hunting, and scavenging to get animal foods into the diet.
So the earliest members of our genius we see in the fossil record about two and a half million years ago.
By about 2 million years ago, we begin to see fossil species like this
So this specimen is about 1.8 million years old. It's from East Africa,
and it's a member of the genus Homo erectus, some people would call it Homo ergaster.
And you can see already, at just about 2 million years ago
a lot of big changes have happened from genus Australopithecus from chapter two.
we've got a much bigger brain size, not quite as big as us yet but bigger than earlier hominins.
The face is much more pushed in it doesn't project as much. And the teeth
are much smaller than Australopithecus.
They're our sized. And this is reflecting a big change in the way this animal is making a living.
Hunting and gathering requires smarts. You have to be able to outsmart your prey to be successful hunting.
It doesn't take as much effort to chew and digest your food because meats very rich and energy dense,
and so the teeth get a bit smaller.
And we also see a big change in the stone tools with Homo erectus.
This development of more and more and more complex stone tools over time,
started again about two and a half million years ago, and continuing through the present day.
So hunting and gathering is this huge change in our evolution.
It makes hominins incredibly adaptable and incredibly successful. So the genus Homo
fills up Africa and starts expanding, bubbling out into the rest of the world, into Europe, into Asia.
And so starting about 2 million years ago, we're not just an Africa anymore.
The genus Homo is getting everywhere, all over the world.
And so we see species sort of bubbling up all over the globe.
Our species, Homo sapiens, is one of these sort of, you know, emergent homo species.
We see our earliest fossil evidence for our own species, Homo sapiens, about 300,000 years ago in Morocco.
But we weren't alone. So 300,000 years ago, as we were evolving, we had Homo erectus still
still in Asia, we had members of the genus Homo in South Africa,
we had Homo heidelbergensis in East Africa, we had Neanderthals in Europe.
So there are members of the genus Homo all over the globe. Were just sort of
one of the later species to evolve about 300,000 years ago.
This legacy of hunting and gathering is something we still live with today, because it literally shaped
our bodies and shaped the way that we work.
Hunting gathering requires you to be smart, requires to be social, and requires you to be very active.
Right and so we can thank our big brains and our intelligence and adaptability
sort of the hallmark of the human species,
we can thank our hunter gatherer ancestors for that, because that's the selection pressure
that pushed our brains to be so big, and our minds to be so smart and creative.
Our hunting and gathering past has also made us really social. So the hunt and gather successfully,
you need to be part of a group, right? It's hunting and gathering.
Some members of the group hunt, some members of the group gather.
And living like that evolving like that, over the past 2 million years
has made humans incredibly social species.
We share meals, we share space, we have, you know, big friend networks. And all of that
is because of this evolution as a very social species as part of our hunting and gathering set of adaptations.
And lastly, hunting and gathering requires that we're be very active, right?
Apes chimpanzees are actually quite lazy. They don't go very far every day.
They live in rain forests that are full of food for them and they don't have to go very far to get it.
Hunting and gathering on the other hand requires that you go long distances to get
plant foods or to chase down game.
And so hunting and gathering requires that we move to be good at getting our food to be able to get our food
And we have that legacy today as well, because we know that if we exercise and we stay active, our bodies,
which are evolved to be active, are much healthier.
And if we're lazy, like our ape ancestors, we get sick.
So we think about human evolution, and that 7 million years of history that has shaped us,
we can see that not only does it help us understand how we connect to the rest of natural world,
but it also helps us understand how our bodies work today and how to keep them healthy.