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[MUSIC] In the previous segment, we saw that there were once many different
species of humans on planet Earth. There are differences between these human
species but there are also similariites. The all belonged, after all, to the same
genus, the genus ***. Now all human species, both the big ones
and the small eh, *** erectus and the neanderthals, they all shared several
defining characteristics that make them all humans.
The first defining characteristic of all human species is that they all had
extraordinaly large brains. when you compare them to other animals.
Mammals weighting 60 kilograms usually have a brain, and the, and the size of
the brain is usually about 200 cubic centimeters.
In contrast, a *** sapiens weighing 60 kilos have a brain averaging between 1200
and 1400 cubic centimeters. The brain -- this is *** sapiens today.
The brains of earlier humans were smaller, but even the brain of the
earliest men and women, in East Africa about twp and a half million years ago,
it was still very large compared, say, to the brain of a tiger of an equal weight
or of a pig of an equal, equal weight. This disproportion of a very big brain
compared to body size only increased as humans evolved.
Now the fact that humans evolved larger, and larger, and larger brains, may seem
to us obvious. We are so proud of our big brains that we
tend to assume that when it comes to brains, more is always better.
But if this was the case, then evolutionary pressures should've produced
not only humans with very big brains, but also cats with very big brains and dogs
with really big brains, and birds with big brains and so forth.
And this did not happen. The fact is that a big brain, aside from
its advantages is also a very big problem.
First of all, you have to carry it around.
It doesn't help you if you have a brain and you leave it at home.
So you have to carry it around with you all the time.
And you have to protect it so it's usually is encased within a massive eh,
skull with all these bones protecting the brain.
And it's hard to carry around, it's, it's burdensome to the body to carry around
this big head with the big brain inside it.
What is even more hard is to fuel the brain with energy.
In *** sapiens, in us, the brain accounts for about 2 or 3% of total body
weight. But, it consumes 25% of the body's energy
when the body is at rest, not running after a giraffe or something.
By comparison, the brains of other apes, like chimpanzees or gorillas, they
require only 8%. Of, of, the energy of the body and even
apes have very, relatively very large brains.
So the big problem with the brain aside from carrying it around, is how to fuel
it with energy. Ancient humans paid for their larger and
larger brains in two main ways. First of all they had to spend more time
looking for food. Whereas a baboon with a smaller brain
doesn't need so much food. So it sits around in the sun doing
nothing much of the day. A human with this big brain, all the time
have to go around looking for food. To eat something so it will be energy to
fuel the brain. So this is one way that humans pay for
the brain. A second method eh, for paying the energy
budget of the brain is that humans became, as the brain got bigger, humans
became less muscular. The muscles became smaller and weaker.
This is a little like a government, which deflects money, which moves money from
the defense budget to the education budget.
So humans began to moving energy from muscles to brains.
From a bicep to neurons, less muscles, so the muscles don't need much energy.
You can divert this energy to fuel your brains.
Now eh, this idea of a, a, a, giving up a muscle in order to have a bigger brain,
it's far from obvious. That this is a good idea.
That this is a good strategy for survival in the Savannah.
A chimpanzee, for example, cannot win an argument with *** sapians but a
chimpanzee can rip apart a human being as if it was a rag doll.
A chimpanzee that weighs 60 kilograms is estimated to be at least five times
stronger than a human being weighing a equal weight of 60 kilgram.
So this, giving up on muscles in exchange for brain it wasn't necessarily such a
great idea such a, such a good deal. Now today this deal sounds very
advantageous to us. Because our big brains really pay off.
Thanks to our big brains we have cars, and we have guns.
So we can drive, much, much faster than a chimpanzee.
And we can shoot the chimpanzee from afar.
So we are, much, much more powerful. But this is only today.
If you go back two million years ago, there is very little that human beings
got from their big brains. Their brains kept growing and growing but
apart from some flint knives and pointed sticks, humans had very little to show
for their big brains. honestly speaking, the evolution of the
human brain, why it became so big, is one of the greatest mysteries in evolution.
We don't really know what drove eh, the growth of, of the human brains.
Over hundreds of thousands of years in which It didn't seem to be doing anything
special. It's very important in general in science
that if you have a very important question that you don't know the answer
to this question, then just be honest about it.
Just say we don't know. I don't know So this is the case with big
brain. It's very important to know why the brain
of our ancestors got bigger and bigger but we don't really have a good answer to
this question. So this is the first quality common to
all humans, big brains. Another quality which is common to all
human species. Neanderthals.
*** erectus. Us.
*** floresiensis. Is that all of us humans walk upright on
two legs. We don't walk on all fours like most of
the other mammals. Eh, it's easier to explain the advantages
of walking upright than the advantages of the big brains.
When you stand up, when you walk on only two legs, and you stand up, it's much
easier eh, to scan the Savanah in, in search of prey or in search of eh,
enemies and predators, like eh, eh, lions and elephants.
You can see them from much further away. Moreover once your hands are freed from
from you don't need your hands in order to walk.
You don't have to walk on all fours. You walk only on, on two legs.
And the hands are free. You can use your hands for many other new
purposes, like signaling your friends, I'm here, or like throwing stones and
throwing sticks, so this is another big advantage of, of walking upright, the
hands are free. And once the hands became free from
walking, humans over generation evolved an increasing concentrations of nerves,
and finally small finely tuned muscles. In the palms and in the fingers.
Which enables humans to preform very complicated, very delicate tasks with
their hands. Like, for example, producing tools and
using tools, stone tools and, and, and sticks and spears and things like that.
The first evidence we have for humans producing and using tools dates back to
about two and a half million years ago. in East Africa.
And from that, this is actually, this is the first sign that we are dealing here
with humans. The manufacture and use of tools is a
defining characteristic by which archaeologists recognize ancient humans.
So these are the big advantages of walking upright.
You can see farther away, that you can have free hands, and then you can start
making and using tools. However, everything in evolution comes
with a cost. Nothing is for free.
And, walking upright also has its downside.
The first problem with walk upright is that the skeleton of our primate
ancestors evolved for millions upon millions of years.
To support a creature that walked on all fours.
And had also a relatively small head and small brain.
Now, when humans moved to walking upright on just two legs, and simaltaneously they
had bigger brains and bigger heads. This created very big stress on the spine
and on the skeleton, and on the muscles in general because again when you take a
creature that walks on all four and suddenly the, the skeleton and the
muscles have to adjust to walking just on, on two legs and to support this big
weight on top of the, of the head. This creates a lot of problems.
So the skeleton and the muscles they, over the generations evolved to do it
better. But, it was never perfect.
And even today, people still suffer a lot from back aches and from stiff necks and
from all kinds of other problems in the skeleton and in the muscular system which
result from a moving to an upright position, so this one this that humans
paid for walking upright. Women paid extra.
Women had to pay something more eh, eh, for walking up, upright on two legs than
men did walking upright. One of the things that happens when you
walk upright is that you're hips have to be relatively narrow and close to one
another. In women this also means that a birth
canal must be narrow. The birth canal is this passage through
which the baby is born. And this created a huge problem because
it's roughly the same period women had to give birth to babies through a narrow
birth canal at the same time that the brains and the heads of the babies became
bigger. So, how, this was a very big problem in
human evolution. How to give birth, to babies with big
heads, through a narrower and narrower birth canal.
Em, this was a big problem. And one of the outcomes was that women
and children began to die during child birth more and more.
Death in child birth of both the babies and the mothers became far more common
among humans Then among chimpanzees or baboons or zebras or elephants.
Again because they had to, to manage these two things together at the same
time to walk upright so you have a narrow birth canal and to have big brain so the
baby has a large head that has to fit through the narrow birth canal.
What was the solution to this problem? So the solution to this problem was to
give birth to babies earlier and earlier when they are still small and especially
when their head and brains are still, still very small and supple.
Obviously, it wasn't a conscious solution.
It's not like two million years ago. men, women, came together in a big
conference, a big meeting. And scratched their head, and said, okay.
How do we solve this? And somebody said, let's give birth
earlier. And this is what they did.
Obviously, it wasn't like this. The solution was given simply by natural
selection. Women that gave birth relatively late,
they had a greater chance of dying in childbirth.
And so they had a smaller chance of of their genes moving to the next
generation. Women that gave birth earlier, when the
child was still undeveloped, rather small with a small head, they had a better
chance of surviving and passing on their genes to the next generation.
So over time the pregnancy period of women became shorter and shorter and
women began to give birth earlier and earlier.
and even today, women give birth to, to human babies much earlier comparatively
than any other animal. Humans so to speak are born prematurely.
When they are only half baked. Like you take the, the cake from the oven
when it is still only half baked, it's not ready yet.
This is how humans emerge from the womb when many of the vital systems,
especially the brain are still not developed, or still under-developed.
When you're comparing this respect, humans with other animals, you see a big
difference and a small horse, a colt. Can start walking and troting very
shortly after birth, within hours of being born, a small horse can start
walking. If you have cats at home, you may know
that a kitten can leave its mother and start walking around by itself looking
for food and playing with other cats when it's only a few weeks old.
Human babies, on the other hand, remain helpless and completely dependent upon
their elders for many months, and even years.
It takes years for the human baby to catch up with what a horses, baby horses
and baby kittens can do. So, this was the solution, the
evolutionary solution, how to walk upright.
With big heads, the solution was to give birth to babies earlier, when they are
underdeveloped. And this had immense eh, importance for
the future of eh, of humankind and for our societies today.
Due to several reasons. First of all, because human children are
born prematurely, they need a lot of care and attention.
From eh, from the, from their, from their elders or parents, from their siblings
and so forth in order to survive and grow up.
In order for a human child to survive, you need to give it much more care and
much more attention than in order for a kitten, to, to survive and to grow up.
Uusually a single mother cannot give to her baby enough care and attention only
by herself in order that it survives and grows up and reaches maturity.
So there's a saying, a famous saying, that it takes an entire tribe to raise a
human. We need help from a lot of people, in
order to raise your child. And this is why humans evolved very
strong social ties with one another, and from missionary pressures.
Eh, natural selection favored humans who are capable of forming strong social ties
and living in tribes. Because this is essential for taking care
of the babies. A grown up can survive by himself or
herself It's not easy but it's possible. But they won't have children.
If you have children the only way that you can take care of them until they are
old is if you have assistance from other humans and therefore humans live in
tribes. Or in groups.
So this is the first big impact of the fact that humans are born underdeveloped,
half baked. The second important impact is that
humans can be educated and humans can be socialized to a far greater extent, to a
far greater degree than any other animal. Most mammals emerge from the womb of
their mothers like some porcelain vase emerging from a kiln.
It's ready. And if you now try to change the shape of
this porcelain vase then you will only scratch it or break it.
In contrast, humans emerge from the womb of the mothers like molten glass emerging
from a furnace, it's still very liquid some, somewhere between liquid and solid
so you can take it and you can spin it and stretch it and shape it into all
kinds of shapes. So this is what's happening with humans.
You can, after they are born, educate it. You can educate them, and you can
socialize them in various ways, and this is why today we can educate our children
to become Christians or, or Buddhist Capitalist or Socialist, war-like or
peace loving. It's all because our brains eh, we emerge
from the womb with half baked bodies and brains and you can still be, you can
still play with us to a large extent. So this is the eh, another important
characteristics of humans, that they can be educated and socialized more than
almost any other animal. We tend to assume, that having a large
brain, being able to produce and use tools, having a complex societies are
huge advantages, and it is obvious, why humans that possess all these advantages
became the most powerful and most important animals on earth.
But the surprising and important fact is, that humans enjoyed all these advantages.
Big brains, tools complex societies, for more, more than two million years.
And during these years, they remained weak and marginal creatures.
Without much impact on the environment. Counting all humans together all over the
world, from Indonesia to, to Britain. Though less than one million humans,
about say a million years ago. And they, they were not the top predators
of the ecosystem. They were not top dogs.
Actually they were preyed upon, they were hunted.
By bigger animals such as lions, and bears, and alligators.
Humans themselves were not very good hunters.
They were rarely able to hunt by themselves big animals like giraffes or
elephants. Most humans subsisted by eating vegetable
vegetable foods. Like nuts and fruits, and mushrooms and
things like that. By hunting small animals like rabbits and
frogs and turtles. And also, by eating the leftovers of
other animals. Like a lion would come and,
hunt a giraffe. And humans will come later on as
scavengers and eat whatever is left. One of the most common uses of early
stone tools was actually not to hunt animals but to crack open the bones of
dead animals in order to get the marrow. The marrow is the black stuff inside
inside bones so this is one of the things that ancient humans probably ate.
Actually, some researchers believe that eating marrow was the original niche, the
original speciality of humans in the world.
Every animal, I mean many animals have a, a special niche in nature.
For example woodpeckers. this is a kind of bird which has a, a, a
strong and sophisticated beak which enables wood peckers to peck inside wood
to make holes in tree trunks and pull out all kinds of termites and worms and
insects that live inside the wood and eat them.
And this is the niche, this is the specialty of woodpeckers.
So, just as woodpeckers have their specialty, ancient humans had their
specialty in nature, which was to eat marrow, to eat the marrow inside bones.
Why marrow? Well, imagine that you're a human a
million years ago and you see a lion take down a big giraffe.
Now this is very tempting to try and eat something from this, a giraffe steak, but
you don't want to go anywhere near a hungry lion because he may eat you as
well as the giraffe so you stay away. You hide and you watch the lion eating
giraffe but you stay away. And eventually the lion had his fill, and
goes away. And it's, it's a big giraffe.
There was still something to eat. But, you don't dare to approach the
giraffe, yourself. Because now is the time of the bigger
scavengers. Like the hyenas, and the wolves, now
it's, it's their turn. You don't want to mess with the hyenas.
So the hyenas come and eat whatever is the lion has left, and you and your
friends, you still stay away hiding, and watching carefully.
Eventually, the heyenas goes, go away and the jackals and the wolves, they all go
away. And only then, you and your friends
approach the carcas of the giraffe looking left and right all the time very
frightfully. Maybe a lion or a heyena is coming.
And when you see that nobody is coming you approach what remains of the giraffe
and you usually find out that there is nothing left to eat.
Because the lion, and the hyenas, and the wolves, they just finished everything.
The only thing that is still left to eat, from this giraffe, is the marrow inside
the bones. Because in, in big bones neither lions
nor heynas nor jackals, they don't have the force in their jaws and in their
teeth to break open large bones and eat the marrow inside.
And now it's your turn, humans. You and your friends, you come, you pick
up one of these big giraffe bones. And you take out your big invention, the,
the, there's the flint knife and you take the bone and you cut it open, and you
break it open, and you eat the marrow and this is your specialty, what humans are
famous for. In the Savannah, a million years ago,
they can break open the bones and eat the marrow.
So these are humans, a million years ago. And it is a key to understanding our
history and psychology even today to realize that the position of humans in
the food chain for close to two million years was somewhere in the middle.
We're not top predators. We're somewhere in the middle of the food
chain for hundreds of thousands of years. Yes, our ancestors hunted small animals
like these turtles and birds and then whatever but all the time, they were
being hunted. By the large predators, and they were
usually unable to hunt big animals by themselves.
Only about 400,000 years ago, several species of humans like neanderthals began
to hunt large animals on a regular basis. And only in the last hundred thousand
years, with the rise of our species, *** sapiens, only then, in the last hundred
thousand years, did humans jump from the middle to the top of the food chain and
became top predators of planet Earth. This spectacular leap from the middle to
the top of the food chain had enormous consequences.
Eh, not only in what, people could, could eat and do, but also psychologically and
socially. Humans were not used to being at the
summit of the food chain and they were actually inadapted for this position.
Other animals that that are at the top of the food pyramid.
Like lions, and sharks, and alligators, and birds, they evolved.
To fill this position of, of, of top predator over millions of years.
So they're used to it. They know what to do with it.
Human kind, on the other hand, ascended to the position of top predator of the
planet almost overnight.In evolutionary terms It took us almost no time to jump
from the middle to the top of the food chain and it was not enough time for the
humans to adapt themselves to this new position.
Many historical calamaties, many things about the way that humans behave towards
others and toward the enviornment. From the deadly wars between humans to
the ways that people treat the ecosystem around them.
Many of these things result from this over-hasty jump.
That we now fill a position in the ecosystem which is completely different
from the position of our ancestors until a very short time ago.
And we are just not used to it, and not well adapted to it.
Sometimes we think about ourselves, human kind, as a pack of wolves that somehow
got hold of tanks and atom bombs. This is wrong, It is better to think
about ourselves as a herd of sheep. Who due to some evolutionary accident
learned how to make and use tanks and atom bombs.
And armed sheep are far more dangerous than armed wolves because they are not
used to it. And they don't know what to do.
How to behave in, in, in, in a position of power.
Wolves know what, what to do with power. And sheep and humans know far less what
to do with power. How exactly did we make this sudden jump,
from the middle to the top of the food chain?
We will begin exploring this question in the next segment of this lesson.