On the shores of a sandy lagoon,
murky water ripples.
Fragments of soden flatsom lap softly at
the shaded shoreline.
It pushes against the snouts of thirsty
assembled deer. The movement is so
gentle, even the most skittish of the
herd scarcely notices it.
But with every ripple, every tiny surge
of the soupy water, a deadly predator
inches closer.
The crocodile is all but invisible at
the water's surface. With just her eyes,
nostrils, and a few scales of her back
exposed to the air, looking like nothing
more than a waterlogged branch.
She watches unblinking as a young but
wary deer steps one hoof into the water.
A calculating killer poised to strike.
She smells the air, sensing the thinning
of the herd that will soon see her prey
move out of reach.
And through special receptors across her
chin and snout, she detects the currents
in the water that will inch her closer
without having to move a muscle.
She waits perfectly motionless until the
time is right. And finally, she leaps.
Exploding from the water 20 m an hour,
powered by limbs and tail of pure
muscle, she lunges for the deer with
gaping jaws filled with dagger-like
teeth.
Clamping down on the unfortunate leg,
she immediately reverses her movement,
pulling herself and her catch back into
the water. As the rest of the herd
abandon the victim in a stampede, the
young deer struggles, straining and
kicking out, but there is no use. Its
limb is trapped in the predator's
vicelike grip,
[Music]
dragging her thrashing prey into deeper
waters, the crocodile switches strategy
again, tucking her limbs close to her
body, raising her tail, and spinning it.
In turn, spinning her body at more than
one full turn per second with the deer's
limb still clamped in her jaws.
As the limb is torn from the deer's
body, the splashing water is stained
red.
From shock and blood loss, the animals
struggle slows and stops.
And the crocodile drags its kill
underwater, leaving nothing more than a
rapidly dispersing pool of blood, ripped
flesh, and senue to join the flatsom on
the surface.
[Music]
It won't be long before the thirsty herd
returns and the crocodile or her kin
will hunt once more.
[Music]
This ambush predator's attack is born of
reflex and raw instinct, shaped and
enacted by a brain that has remained
virtually unchanged for an astonishing
200 million years.
The way she processes her surroundings
and hunts today is an echo of her
reptilian ancestors of the deep
prehistoric past.
coordinating her body, navigating the
environment, and responding to changing
situations without a moment's
hesitation.
[Music]
Indeed, not surprisingly, considering
their wild evolutionary success,
crocodiles are considered one of the
most intelligent hunters on Earth.
Despite having brains that are barely
larger than a walnut, far smaller than
their prey, making up just a fraction of
a percent of their body mass,
this highly efficient biological
circuitry is all the reptilian predator
needs to ensure its ecological
dominance.
And yet, there is much the crocodile
lacks.
The reptilian brain is stripped down to
its raw survivalist basics. And when
this ruthless, lethal predator is
compared with the humans who watch the
unfolding scene from a safe distance, or
even the big cats and other mammals
roaming the savannah nearby, there are
deficiencies in the reptile mind that a
crocodile is incapable of even
considering.
No complex memories, no moods or
emotions are to be found here.
Just the instinct of hundreds of
millions of years of the kill.
No judgments are made, no anxious
searching, no contemplation, just
reflexive, albeit intelligent responses
to streams of incoming data,
acting accordingly in ways that will
further their evolutionary goal,
regardless of what happened yesterday or
what might be happening tomorrow.
worlds completely unknown to these most
powerful of predators.
[Music]
In the 250 million years since
crocodilians first appeared on the
planet with a similar heritage to the
dinosaurs, evolution has honed the
brains of these living fossils into the
ultimate predatory processors.
But in doing so, they have missed
opportunities that their mammal cousins
and much later primates and humans have
been able to pursue.
Entire brain regions are left
languishing inside the reptilian skull.
While in mammals, they have blossomed
physically and metaphorically into
organic computers with behaviors that
are ultimately far greater than the sum
of their parts.
[Music]
Somewhere along the way, the physical
circuitry of the brain became the
psychological reality of the mind.
Consciousness, sentience, and sapiens
combine to make humans and other animals
into something else, something more than
just machinery.
But none of this would have been
possible without the building blocks
that came hundreds of millions of years
before.
Today, the brain is the most complex,
expansive, and interdependent organ in
the human body.
The secret to our success.
the only reason we can converse at all,
seek out art, culture, and build our
civilizations.
But if we wish to understand how the
brain came to be, we need to go back to
the very beginning,
far before the first mammals and even
the ancestors of the crocodile to the
dawn of animal life itself.
Thanks. Now back to ancient Earth. [Music]
When 25-year-old Phineas Gage was
employed by the railway construction
companies of New York and Vermont, New
England was a place of great expansion.
The year was 1848 and like many of his
countrymen, Gage would play his part in
the heady expansion of railroads across
the northeastern United States.
His peers described Gage as strong in
both mind and body, bringing an iron
will and persistence to anything he set
his mind to.
He was smart, shrewd, energetic, and
well-liked.
And it wasn't long before he was raised
to the position of foreman.
But in September of that year, Phineas
was using explosive charges to clear
ground for the Rutland Railroad in
Vermont when he became the victim of a
tragic accident.
While packing sand and explosives into a
prepared hole with an iron rod, the
gunpowder unexpectedly ignited, ripping
the meter long, 3 cm thick tamping rod
out of his hand and propelling it like a
rocket upwards towards his face.
Gage had just opened his mouth to speak,
and the iron rod smashed through his
upper jaw, cheekbone, behind his left
eye, and directly into his brain.
[Music]
The rod's full length ripped straight
through the left side of the organ and
smashed out through the top of his skull
before continuing its journey through
the air.
Coated in blood and brain had landed 25
m away.
Gage himself was knocked backwards onto
the ground, but to the amazement of his
fellow workers, he soon sat up.
Astonishingly, within minutes, despite
the gaping hole in his skull, he was
walking and talking again.
As he rode an oxcart back home, he took
the opportunity to update his time
sheets.
The physician who examined him soon
after said that he could see Phineas's
brain pulsating through the top of his
skull. And when the injured man vomited,
he reported seeing a teacup full of
brain matter exude and fall onto the
floor.
And yet throughout all of this, Phineas
remained stoically optimistic,
declaring that he would be back at work
within a few short days.
In the end, however, his convolescence
was long and difficult. In the first
week after the accident, he swung from
optimistic and delirious and back to
rational before descending into a near
comeomaos state.
His
friends and family readied his funeral
clothes, expecting him to pass any day.
But against all the odds, Phineas clung
on.
After the doctor had cut into his
damaged face to release the infection
that had developed there, Gage gradually
improved. And by February, barely four
months after the accident that should
have killed him, he was back working on
his parents' farm, albeit with partial
paralysis in his face and no vision out
of his left eye.
However, even as his physical
capabilities returned, it became
apparent that Phineas Gage was a changed
man.
So much so that his employers at the
railroad refused to take him back.
Whereas before he had been driven,
resourceful, and well-liked, now he was
irreverent and uncooperative, stubborn,
and impatient,
behaving in a vulgar way, and prone to
outbursts of swearing. Along with a new
personality that didn't sit well in
social situations, he was unfocused,
devising multiple plans and schemes that
would soon be abandoned. His doctor
described him as having a childlike
manner, but with the animal strength of
a full-g grown man. It was clear his
body may have survived an iron rod
through the brain. But apparently the
man who had been Phineas Gage inside
that body had not.
But this isn't the end of Gage's story.
Although the railroad wouldn't take him
back, he was able to hold down jobs
driving horsedrawn coaches in America
and Chile for the next 10 years.
Over time, becoming more socially
adapted, his personality improved and
his later employers saw no problem with
his behavior.
And finally, in 1860, 12 years after an
iron bar tore through his skull, the man
with half a brain died from an epileptic
fit.
What then does this remarkable story
tell us about the importance and role of
the brain?
We of course consider this organ to be
vital to our survival and daily
functioning. It's unique in the body in
having its own protective bony case and
head injuries are often feared above all
others for what they might mean for our
physical and mental capacities.
And yet, Phineas Gage was able to
continue a conversation while parts of
his brain literally dropped onto the
floor.
Indeed, the worst of his illness was
caused by infection rather than trauma.
Either way, his brain had become
damaged, in particular, his left frontal
lobe. It's this that is thought to have
caused the changes to his personality
while leaving him with his physical
abilities intact.
Indeed, our frontal loes are now known
to be where planning and organization
takes place, as well as being a hub for
social skills and emotional regulation.
When Gage's frontal lobe was damaged,
many of those functions were
shortcircuited,
changing the way he behaved and how he
came across, apparently forcing him to
learn from scratch. And yet, the fact
that most, if not all, of Gage's
original personality returned in time
tells us that the brain is not a rigid
computer made of squishy organic parts.
It is an organ in flux, which can heal
and remap itself to circumn the damage
that is done to it.
Indeed, we now know that this so-called
neuroplasticity is the root of brain
development, resistance, and recovery
from damage.
Phineas Gage is often referred to as the
man who began neuroscience
and certainly his accident and
subsequent recovery occurred at a
pivotal time for the understanding of
the brain,
the central processor for the nervous
system.
One of the most extensive organ systems
within the body, constructed from an
interlinking web of nerve cells,
otherwise known as neurons,
these specialized cells are able to
transmit a small electrical impulse
across their surfaces, which can be
thought of as information moving from
place to place.
This impulse travels at breakneck speed,
typically topping 100 mph.
Individual neurons can be as small as
four microns, allowing up to 2,000 to
fit across the head of a pin.
Meanwhile, other neurons have long arms
called axons that can stretch over a
meter in length and have unique
structures along them that speed up the
transmission of the electrical impulse.
The sciatic nerve, which runs from the
bottom of our spine all the way to our
toes, is made of these exceptionally
long cells. and yet information is
passed along it within just a few
milliseconds.
[Music]
Even the longest neurons, however, are
of little use if they're only
transmitting impulses along their own
lengths.
Instead, of course, they must connect to
other neurons, which themselves connect
to others, and so on. Each neuron is
capable of connecting to more than a
thousand others until the body is
thoroughly penetrated by this organic
wiring.
We rely on these connections for
everything that is actively controlled
within the body. But where one neuron
meets another, there is no physical
connection.
Indeed, the cell's arms reach out to one
another like Michelangelo's creation of
atom writ microscopic, coming
tantalizingly close but never touching.
At these junctures, called synapses, the
neurons branches come to within just 20
nanometers of each other. Despite this
narrow space, a neuron's electrical
impulse cannot bridge the gap. And so,
the cells rely on chemicals to shuttle
information back and forth across a
syninnapse.
When an electrical signal arrives at a
neuron branch's dead end, a flood of
these so-called neurotransmitters are
released into the synaptic space, which
they cross in just a tenth of a
millisecond.
They attach to special sites on the
adjacent neuron and trigger a new
electrical impulse to begin.
Thus, through a complex interconnected
web of electrically conductive cells and
minuscule chemical messengers, the
nervous system links sensing cells like
those in the eyes, ears, nose, and skin
to active cells like those in muscle.
But in the majority of cases, that link
is circuitous,
passing through a processing hub that
helps to make sense of the information
coming and going. And that hub is the
brain.
In humans, the brain along with the
spinal cord form the central nervous
system.
And just as all roads lead to Rome,
every single nerve impulse in the body
is either heading towards or away from
this central hub.
Some impulses are simply relayed from
sense to action. like when we
reflexively and unconsciously jerk our
hand away from a scolding surface in a
similar manner to our crocodilian
distant cousins.
For the most part, incoming information
is assimilated, sorted, and responded to
in a more complex way,
requiring the much more complicated and
interdependent network of neuronal
wiring that constitutes the brain.
And our human brains have grown
unprecedentedly large and influential.
[Music]
Weighing around 1.4 kg, they contain
more than 80 billion neurons, making 100
trillion connections to one another and
transmitting information at over 350
mph.
Constantly running at around 20 watts,
the brain's power would be plenty to
illuminate a light bulb, even in the
absence of bright ideas.
But all that power and complexity comes
at a cost.
And our big brains are expensive to run,
consuming around 20% of all the oxygen
we breathe and the energy we produce.
However, this is not the case for every
animal. Some, like spiders, allocate up
to 80% of their bodies to their brains.
Others, like koalas, don't even fill
their skulls.
Squid, cuttlefish, and octopuses have a
donut-shaped brain that surrounds their
food pipe, meaning that if they eat a
meal too large, they can give themselves
brain damage.
But this isn't as much of a disadvantage
as it might sound because these animals
have a far more distributed control of
their bodies
[Music]
with a greater number of neurons in
their tentacles than in the brain
itself.
In this way, while the central brain can
exert a sort of top- down control, each
of their tentacles can act
independently.
Even the human brain is subdivided to an
extent. As the fateful tale of Phineas
Gage reveals, not every part of the
brain is necessary for every function.
There is the smooth dense cerebellum
that plots our movements,
the limbic system that stores our
memories and is the seat of our
judgment,
and the loed neoortex from which most of
our thoughts and learnings originate.
However, just like our fingerprints, the
finecale anatomy of every brain is
unique to its owner. And somewhere
within that tangled web of neurons and
neurotransmitters amid the chemical and
electrical toing and throwing of a
constant stream of information,
something truly remarkable has emerged
in humans and in many other animals. The
spark of consciousness.
transforming a mere brain into a mind.
[Music]
Most simply defined as a subjective
experience, consciousness is the idea
that to be a human or a crocodile or an
octopus feels like something.
[Music]
that information isn't merely relayed
through the brain, but it's considered
and we somehow become aware of it.
Although we might not always have the
words to describe it, and a crocodile or
octopus certainly can't, we have an
awareness and responsiveness to the
world that lets us experience what it's
like to be human, crocodile, or octopus.
And each species, indeed, each
individual's experience is entirely
unique.
From consciousness comes sentience, the
ability to experience distinct feelings
and sensations, as well as the positive
and negative emotions that those
sensations can invoke.
Indeed, sentience within the animal
kingdom is a strongly debated topic.
It's obviously difficult to measure and
interpret in creatures who don't share
our communication systems.
Instead, scientists carefully observe
behavior and consider the evolutionary
origins of each animal.
As a result, most consider the
vertebrate animals, including all
mammals, reptiles, amphibians, birds,
and fish to be sentient.
as well as a number of invertebrates
including the octopus and its sephilopod
relatives along with lobsters and crabs.
And finally, layered on top of sentience
comes sapiens or wisdom, which is the
ability to think, to learn, and to apply
considered concepts to our behavior,
especially in novel environments.
Those who can think about thinking have
achieved this lofty abstraction.
[Music]
Once thought to be the sole domain of
humanity, most scientists now agree that
whales and dolphins along with
chimpanzees and possibly octopuses
possess this most advanced ability.
[Music]
And so it would be easy to assume that a
larger brain equates to a more developed
one.
and one with greater abilities like
emotional sentience and sapience.
And while big brains may come with more
neurons capable of making more
connections and theoretically more
advanced processing, the widely varying
structure and function of different
animal brains means that the correlation
is not always a straightforward one.
Indeed, crocodiles are some of the most
intelligent hunters on Earth with a
brain that is the size of a walnut.
While shrews dedicate a tenth of their
body weight to their brains, and no one
is arguing for their intellectual
supremacy.
[Music]
But if brains are also different in
size, form, and function both among
animal species and within them, then how
can we hope to find a common theme?
How can we hope to trace them all back
to the first brain?
If every animal uses their organic
processor in a different way, how can we
know how the first brain was used?
Scientists have long pondered this
enigma,
and they've discovered a great deal in
recent years.
[Music]
14 million years ago, an ape balances on
the branch of a spreading fruit tree.
Some 10 m off the ground, she secures
her position with claws that dig into
the smooth bark as her muscles twitch
and correct her movement almost
constantly.
That leaves her front paws, her hands
free to methodically strip the twigs
within her reach, her liy digits, her
fingers make short work of the
protective spines and waxy leaves,
tearing them away to get at the clusters
of small fruits nestled within.
But while her fingers work, her
attention is elsewhere.
large eyes darting among the swaying
branches around her, ears twitching for
the sounds of hoots or bellows that
might give her advanced warning of
approaching threat.
[Music]
She is smart, among the smartest of all
the primates on the continent, and the
baby in her belly will be the ancestor
of the entire human species.
[Music]
And yet, the brain of this ancestral
matriarch betrays nothing of the
revolutions to come.
Inside her skull, the computer that
drives her thoughts and behavior is
similar in size and complexity to those
of gorillas, chimps, and orangutans
today.
It will take more than 10 million years
for that to change.
Some have suggested that it was the
permanent move to walking on two legs
that necessitated our ancestors to grow
larger brains.
But while the first truly bipeedal apes
appeared between 4 and 6 million years
ago, by all accounts, the brains of
these animals, these ancestors, were
still small.
Two-lim walking freed up limbs for
carrying food and offspring in an
everchanging landscape of dense forest,
broken woodland, and savannah.
Indeed, there's little doubt that
bipedalism was an innovation that
allowed human ancestors to stride
through a changing world.
But changing stances wasn't actually
that much of a computational challenge.
And so it wasn't until around 2 and a
half million years ago that the brains
of human apes began to grow larger.
Continuing changes in the environment
forcing them to begin to create and use
tools.
[Music]
They would be simple at first, but an
obsession that will lead to all the art
on planet Earth
and to the device you use to watch this
today.
Those
[Music]
individuals who were born with brains
that were marginally larger and more
complex than their peers had better
dexterity with those tools, allowing
them to survive, reproduce, and pass on
their large brain genes.
Alternatively, rather than the physical
instruments of survival driving brain
growth, others have suggested the
catalyst to be the intangible
development of culture.
Those born with slightly larger and more
complex brains may have had better
memories, emotional sensitivity, and
quick learning capabilities.
And again, those whose brains allowed
them to keep up with the rapid increase
in communal knowledge and the
intricacies of its application were more
likely to survive and thrive.
These are all good reasons why big
brains were favored in the ancestral
human line.
But the question remains as to why it
only happened in this line and not on
the branches of the tree of life that
would lead to the other great apes.
The initial answer may not lie in the
environmental changes or the physical
and cultural innovations nor even within
the brains themselves but in our
ancestors muscles.
[Music]
In all vertebrates the bite muscles are
responsible for closing the jaw and are
the strongest muscles in the face
completely enclosing the skull.
They are so strong that they actually
reinforce the bony carropus of the
skull, holding it together firmly.
However, studies into the genes that
control these muscles development reveal
that they were weakened by a chance
mutation around 2 1/2 million years ago.
Researchers believed that the looser
muscles wouldn't have constrained the
skull's expansion as much as their
unmutated counterparts,
allowing brains to grow larger with less
resistance.
After that, human brain growth seems to
have snowballed thanks to positive
feedback between biology and behavior.
Larger brains needed more fuel, but they
also created opportunities for those who
bore them. Around 2 million years ago,
larger brains allowed early humans to
develop tools that they could use to
kill and butcher larger animals,
giving them easier access to meat than
ever before. Since meat is a richer
source of nutrients than fruits and
grains, this richer diet could have
helped to fuel even more brain growth
and even more hunting prowess.
[Music]
It's also likely that as Prometheus
gifted the spark to humanity in the
Greek myths, the taming of fire played a
pivotal role.
Perhaps begun by chance and yet soon key
to our species very way of life. With
cooked food being more easily digested
and providing more nutrients, this meant
early humans could scale back on the
amount of digestive tissue they needed
and invest those resources into the
brain instead.
In this way, alone among the great apes
and at a faster rate than ever seen
before, the modern human brain came into
existence some 200,000 years ago,
piloting us into the realms of
technology and civilization ever since
in a way that our distant ancestors
would scarcely be able to comprehend.
And yet, heading back to hundreds of
millions of years before, the last
common ancestor of all life on Earth did
at least have a kind of brain to begin
with.
Just like we may struggle to conceive
how life itself, born of other life for
generation after generation, could be
born from non-life in the beginning, we
may also grapple with how something as
complex as a brain could arise for the
first time.
[Music]
But its origins are in fact much deeper
than we might imagine.
[Music]
As far back as 3 billion years ago, or
even earlier in the Archon, the first
bacteria in Earth's oceans would not
have gone very far if they hadn't been
sensitive to the environment around
them. Their metabolisms relied on
absorbed nutrients, including gases like
carbon dioxide and metals like iron and
manganese.
It's very likely that these first
bacteria simply happened upon
nutrient-rich pools by chance, surviving
while their kin, who found themselves in
a molecular desert, simply died.
But there was a lot to be gained for
these simple single-sellled organisms
when they learned to sense and respond
to changes in their surroundings.
[Music]
As single-sellled organisms became more
advanced, the scope of their chemical
sensing followed suit.
Photosynthesizers like the cyanobacteria
that built strumatalytes may have
learned to sense the sunlight, enabling
them to move upwards through blanketing
sediments and stay within its warm
embrace.
And ukareotic cells with their more
complex internal and external workings
became sensitive to myriad chemicals at
once, including ones that they
themselves made.
Indeed, eventually it was the sensing of
its kin that would help single-sellled
organisms assemble themselves into
multisellular organisms for the first
time, too.
The closest single-sellled relatives to
animals are the kuanoflagelates,
feeding on bacteria, most spend their
lives free floating as individual cells.
But some species can also form colonies
with individuals living shouldertosh
shoulder in balls or grapel-like
clusters.
[Music]
The kanoflagelates developed a new way
of communicating between individuals
using electricity.
This electrical signaling and sensing is
similar in many ways to the passage of
electrical impulses through our own
neurons.
And indeed, there's every reason to
believe that the Kanan flagagelates
invention or something very much like it
was the foundation on which our nervous
systems began.
[Music]
Thus, during the distant transition to
multisellularity in those near
unfathomably prehistoric seas, the
ability to sense and respond to the
external environment was co-opted. some
billion years ago or more to help these
larger and more complex organisms sense
and respond to changes within their own
bodies.
This chemical and electrical signaling
that had been around for at least a
billion years ultimately formed the
basis for the earliest nervous systems.
[Music]
In the beginning though, it would have
been far from organized and those
organisms who could make sense of the
electrochemical storm inside themselves
would be the ones to survive.
Chemical signaling is slow, but
electrical signaling has the potential
to be much faster and more direct.
And so gradually order was achieved.
The first electrical neurons and
chemical synapses taking shape within
early animals bodies.
But what role did these nervous systems
play? Why were they needed in the first
place?
Well, today there are two schools of
thought.
The first is that these internal
signaling systems evolved to do what
they had always done,
what they apparently continue to do even
in our own bodies, to sense and react.
This so-called sensorometer view says
that nervous systems evolve to link with
what is sensed, to the action in
response to it. We can see this simply
when we pull away from something sharp
or blink in answer to a bright light in
our eyes. We may not be aware of it, but
sensory motor reflexes are core to our
autonomic nervous systems which detect
changes in our internal conditions like
temperature or dissolved carbon dioxide
and take action among the various organ
systems to keep things working as they
should.
With such obvious examples in our own
bodies and striking precedent from the
single-sellled creatures that came
before, it may seem like this is the
only possible explanation.
But the alternative view takes into
consideration just how different we are
from our distant singleselled ancestors.
It acknowledges that when you're
wielding a body made of many, many
cells, responding to a stimulus is no
trivial matter. and needs to be
coordinated if it's to succeed.
Each muscle needs to be activated in the
correct sequence while its counterpart
for performing the opposite action needs
to relax or else we'd end up splintering
our own bones.
Even considering the action of a single
muscle involves signaling to thousands
of individual muscle fibers.
If any of those failed to get the
message, then the muscle would be torn
from the inside out.
And so, just as it was muscles that
allowed the expansion of the human brain
some 2 million years ago, it was the
invention of muscles in the first place
that set the evolution of nervous
systems and ultimately the animal brain
itself into motion.
[Music]
With an electrochemical nervous system
in place, it's not hard to see how the
earliest rudimentary brains came about.
Concentrating more neurons in a single
place, usually close to the sensing
organs would allow for feedback loops in
the electrical signaling,
creating the kind of logical
dependencies and responses you might
find in a computer circuit.
Information can then be processed rather
than being merely relayed as the
circuits determine whether a piece of
information is significant enough to be
acted upon.
[Music]
Building upon these logic networks, just
as computers do, with an increasing
amount of physical neuronal hardware,
the knots of nerves became hubs and the
first brains were born.
[Music]
It's likely that both sensory motor and
action shaping coordination were forces
driving the evolution of the first
nervous system and brains and may even
have played separate but adjacent roles
in the same organism.
Though no fossils remain due to its
hypothetical fleshy form, scientists
imagine a primitive free floating
jellyfish-like organism. It may have
developed an action-shaping brain to
coordinate movements around its mouth
to help food to move in efficiently.
But it may also have developed a second
neuron hub near the top of its dome
capable of sensing light levels and
triggering the release of a daily cycle
of hormones to keep its internal
machinery working.
And over time, those two hubs may have
migrated or grown together to create a
single brain capable of exchanging
information about the entire body and
the external environment.
[Music]
Once a precedent had been set for
brain-like circuitry, the standard rules
of evolution took hold to favor the
development of larger and more complex
brains in animals that would benefit
from larger and more complex bodies.
Those
who followed a conservative evolutionary
path, evolving towards a simple life of
seafloor grazing or mindless floating,
could make do with the bare minimum of
coordination and response.
But any animal that attempted to grow
large, move fast, or adopt new
ecological roles needed cognitive
circuitry that could cope with the
challenges those niches posed.
[Music]
And in the end, this proved to be the
arropods with a need to coordinate their
jointed legs, the cordates, including
all fish, mammals, reptiles, amphibians,
and birds,
and a single group of molllesks that
grew arms, the sephalopods.
[Music]
Although later on among each of these
groups, scientists have seen that it's
not just the physicality of an animal's
body that drives brain development, but
also the challenges of social
organization.
Animals that live socially also need to
consider the behavior of others in their
neuronal logic, adding an extra level of
complexity to the mental work they must
do.
[Music]
However, in general, having a brain,
even one that has been boosted by the
demands of social living, doesn't
necessarily equate to having a mind or a
subjective experience of the self.
Indeed, the earliest brains were still
most likely fully autonomous and
unconscious.
Awareness, feeling, and sentience would
come later.
that most fundamental aspect of the
human condition initially emerging as
unintentional properties of the organic
wiring within the brain.
[Music]
In a mmoration of starings, each bird
follows a simple set of rules to stay
aloft, to stay alongside, but to avoid
its neighbors.
[Music]
Viewed from a distance, the entire flock
creates dynamic shifting shapes that
startle in their beauty and complexity.
It's hard to pinpoint the scale at which
flight turns to art, just as it is hard
to pinpoint the precise origins of
consciousness.
Some researchers think the awareness of
the self is a relatively late
development.
That you need to be able to hold
multiple inputs, memories, and
conditions together to be able to
experience their results.
An alternative perspective suggests that
the fragments of consciousness can be
assembled gradually
with primitive feelings emerging like
magic eye pictures out of the white
noise of sensation.
Indeed, this means the first to appear
may be the base primordial feelings like
pain and thirst.
By studying how animals respond to an
injury, scientists do their best to
establish whether they are experiencing
pain as a conscious feeling.
Whereas crabs and shrimp groom and fuss
over damaged legs, their insect cousins
never seem to notice entire missing
limbs.
On this basis, the former group are
considered sentient while insects are
not.
There is of course an evolutionary
advantage to feeling these primal
emotions.
Awareness of them allowing more than
just reflective responses.
This means that animals can remember and
avoid things that cause them pain
or act preemptively in the future to
avoid thirst.
And so over evolutionary time, these
isolated intrusive feelings become more
coherent. And others may join to build a
more complex mind alongside the
complexifying brain that can support it.
And so from its origins in the sensory
systems of archen bacteria through the
coordination of multisellular creatures
and the unique demands of social
survival, the brain has become an
essential part of animal existence.
But have brains and animals always gone
hand in hand?
And which truly came first?
[Music]
The warmth of the sun kisses your skin
as you drift from sleep to waking.
[Music]
You idily stretch into its embrace,
feeling the gentle flow of water against
your arms,
opening one eye and then the other.
You're momentarily blinded by the early
morning glare, spearing down into the
cave.
But it's not long before your vision
adjusts and the world before you
resolves into glittering crispness.
All is as it was before you slept. And
as you shake the last of the night's
groggginess from your limbs, you waste
no time in clambering from the comfort
of your den, striking out in search of
food.
You traverse your usual route across the
rocky field, turning over small rocks,
probing the crannies for shrimp or
snails, anything that can sate the
nagging hunger that the morning always
brings.
when suddenly the sun is eclipsed and a
strange smell tugs at your senses.
You whip around to catch a glimpse of
the intruder and linger on the long
enough to make out a vast shape floating
not three arms lengths away. It's huge,
many times your size with skin that is
black and smooth.
The sunlight glints menacingly off its
wide, flat eyes, as well as the curving
shell on its back, and its four limbs
jerk and fold rigidly in horrifying
symmetry.
As a cloud of bubbles burst forth from
its mouth, you are already turning to
flee.
Your body responds to the terror above
without troubling your conscious mind.
Your skin shifts from its usual smooth
reddish orange to a textured gray,
blending in with the rocks and sand of
your hunting field.
You're already moving, your eight arms
taking turns to push and pull you away
from the floating horror as you release
your ink along with a pulse of water
through your siphon.
Concealed by the black cloud, you tuck
your arms in behind you and jet away,
keeping one eye on the unknown threat.
All thoughts of your empty belly
forgotten.
But for all its size and strangeness,
the alien creature is slow. Or at least
it doesn't seem inclined to attack.
Having reached the safety of your den,
your skin is now black, so you can melt
into the shadows.
But your eyes are still open, and you
watch as this thing awkwardly bends and
folds its unggainainely limbs to
clumsily navigate the reef.
The bubbles continue to rise, but they
don't seem to offer protection or speed.
You begin to think that this creature is
as harmless as the basking sharks that
sometimes visit. So, you creep over to
the entrance of the cave for a better
look.
You watch it poking about the reef, and
as awkward as it is, it does still move
with purpose. Climbing across the rocky
field with a kind of methodical drive
that reminds you of yourself.
[Music]
There is something behind those flat,
glassy eyes, something very much like a
mind.
The next time it passes close, you
stretch out one sucker tentacle to greet
it.
[Music]
Octopuses and humans, like the ones in
this interaction, both sit in the upper
branches of the tree of life. They are
granted this lofty position not because
they are the pinnacle of evolution.
Indeed, in a process that is always
ongoing, there is no such thing. But
because they just happen to be alive
right now,
contrary to what the early philosophers
of science imagined, evolutionary change
doesn't look like a ladder, beginning
with a primitive organism, which then
transforms stepwise into an ever more
advanced one.
Rather, the changes that are wrought
over millennia create new organisms that
can adapt to their unique environments.
While the original lineage also
continues to exist and transform
this way, evolution does create
incremental change. But much more
significant are the splits that build a
densely branching tree of life.
Each branching point represents the
moment that two creatures diverged their
last common ancestor.
[Music]
And the deeper the branches, the more
fundamental the differences between
animal groups and in theory, the more
separated they will be at the top of the
tree.
This means that if we look around our
fellow animals at the top of the current
tree of life, our closest neighbors will
be the ones to whom we are most closely
related.
[Music]
the great apes and other primates.
Together we sit within a sea of mammals,
and in the distance we might see birds,
relatives, fish, and amphibians.
The octopuses, by comparison, are far
more distant, accompanied by squid and
cuttlefish,
almost lost among a crowd of their
fellow invertebrates.
They are so distant that when we trace
their branches back through time using
genetic evidence, they do not connect to
our own for some 750 million years.
They have been diverging from us for
almost as long as animals themselves
have been around.
And yet, despite their differences,
their distance from us at the top of the
tree, and their deep evolutionary
separation, both human and octopus seem
to share something unexpected.
The spark of sentience inside their
brains, inside
their minds.
Humans are among a select group of
mammals that have large and complex
brains
and which show levels of consciousness
and sentience that these organs
seemingly allow.
[Music]
But octopuses also behave in ways that
make scientists believe they are
sentient and intelligent.
Along with cuttlefish and squid, these
seephalopods are clearly elevated above
the other mollisks in their kin in terms
of what they can do and how they react
to the world around them.
Given the depth of octopuses and humans
evolutionary separation and the myriad
organisms along each of their branches
that don't share this particular spark,
it's clear that large and complex brains
must have evolved independently along
both of these branches.
[Music]
And considering the last common ancestor
of these organisms existed at such a
pivotal time for all animal evolution,
it's natural to wonder what the brains
of this common ancestor looked like and
exactly when the seeds of sentience were
sewn.
There are several ways that we can try
and pinpoint the origin of a specific
organ like the brain.
Molecular clocks make use of the
universal language of genes and proteins
that help to build every piece of
organic machinery on Earth.
Scientists realize that proteins mutate
at a constant rate throughout geological
time
and have used these calibrated clocks to
estimate when the genes that code them
came into existence.
Using these methods, the genetic origin
of the nervous system has been pinned as
far back as 700 million years ago.
During the cryogenian period, when the
planet was gripped by a seemingly
inescapable ice age lasting some 100
million years.
Unfortunately, both the inhospitable
conditions on Earth at the time and the
likely softbodied and microscopic nature
of life at the time make the existence
of any physical evidence from the period
unlikely.
Not only that, but there are plenty of
assumptions about molecular clocks,
which may or may not hold true over such
a vast gulf of time.
Do the proteins and genes mutate at a
constant rate? And are the brain coding
genes even the same as they always have
been?
It's clear that more evidence is needed.
And so an alternative approach is the
more traditional one used by
paleontologists
in tracing the organ itself back through
the fossil record.
This method has been used with great
success to track the evolution of
vertebrate skeletons, molllesk shells,
and plant structure.
But despite the nervous systems
importance to animals, its strictly
cellular nature has offered little in
the way of fossil record, even in
relatively recent times.
Indeed, the unmineralized soft tissue is
one of the first things to decay upon an
organism's death,
making its long-term preservation
vanishingly unlikely.
But there are still clues to be found in
the parts that do end up being
fossilized.
Most of what we know about brain
evolution among ancient humans, as well
as all vertebrates, comes from
endoccasts.
These three-dimensional molds are
created by sediments that get inside the
enclosing carropus of a skull long after
the brain tissue has rotted away.
Sometimes paleonurologists make the
endoccasts themselves,
filling a fossil skull with plaster to
create an impression of the space
inside.
[Music]
And once in a while, these endoccasts
can contain something more.
In 2004, an animal fossil collector
found a strangely shaped lump of rock on
a beach in southeast England, which
turned out to be the brain-like
endoccast of a 130 million-year-old
relative of the dinosaur Iguanadon.
But the outer surface of this lump also
retained details not commonly seen in
sedimentary brain molds.
On closer inspection, this cast
contained blood vessels and capillaries
thinner than a human hair, as well as
some textures of cortex tissue and
membrane.
Ripples in that membrane were
reminiscent of the folds that may have
been present on the surface of the
dinosaur brain.
But unfortunately, the pickling process
of the Cretaceous swamp was unable to
preserve the neurons themselves.
Despite this, it is clear that
endoccasts can be surprisingly
enlightening.
Studying them among animals that are
closely and distantly related to one
another allows paleonurologists to track
the development of brain regions across
disperate groups and through geological
time.
The 130 million-year-old iguanadon brain
endoccast appears to have an overall
structure that is similar to the brains
of modern-day crocodiles and reptiles.
And although intelligence is only
loosely related to brain size,
scientists estimate that the ancient
animal was at least as smart as a modern
crocodile.
But there is also much that the
endoccasts can't tell us.
The complete absence of internal brain
anatomy means that it's impossible to
identify structures like the hippocampus
and basil ganglia in humans.
And of course, skull endoccasts can only
be formed for animals that had a skull
in the first place.
This method can tell us nothing about
brain evolution in the other 95% of
animal life.
However, though the fossil preservation
of delicate organic tissues is extremely
unlikely, it isn't impossible.
Sometimes sedimentary conditions
conspire to inume purely organic tissues
before decay can take place.
And in the comparatively virgin waters
and sediments of the Cambrian period
some 500 million years ago, this
fortuitous preservation happened
surprisingly regularly.
Animals died and fell into dense clays
on the seafloor where their bodies were
trapped, compressed, and isolated before
much decay could take place. Their body
tissues were then replaced by a kind of
rigid carbon plus phosphate and clay
minerals preserving organic details with
remarkable clarity.
With this process occurring throughout
the deceased animal, organic rich films
in these exceptionally preserved
flattened fossils give paleontologists
an unprecedented window into the nervous
systems of some of the earliest animals
on Earth.
One such animal is Stanley Carus, a
radioodont that is related to the
fearsome predator Anomal Caris, to whom
we dedicated an entire documentary.
But Stanicaris rarely grew longer than
20 cm.
The animal had three eyes, two raised
upon stalks and another large central
eye in the center bulge of its head. And
in at least 84 specimens recovered from
the 56 millionyear-old Burgess shale of
Canada, scientists are able to see the
brain behind those eyes as well.
These flattened fossils show a dense
accumulation of carbonri tissue inside
the animals heads.
The brains are formed of two segments
connecting the eyes and the front claw.
And researchers believe that they can
trace the visual processing center that
links the eyes as well as the nerves
heading into the flexible grasping
appendages.
Another relative of the predatory animal
is a gild loapod called kerigma
known from rocks in northern Greenland
that are between 530 and 515 million
years old.
And in this animal too, scientists have
found carbon impressions of a
diminuative brain that connects the eyes
and the frontal appendages.
In this older specimen, however, there
seems to be only one central section to
the primitive, even pre-retilian brain.
A recent discovery from China, however,
casts an even more illuminating light on
the evolution and role of early nervous
systems.
Cardiodiction is an armored loapod, a
member of an extinct group of softbodied
invertebrates that are most closely
related to the velvet worms of the
southern hemisphere.
In 2022, paleontologists reported
finding an intact specimen among the 525
millionyear-old Cheng Jang fauna of
Yonan, China.
The flattened fossil is just 1 and 1/2
cm long, but is preserved in exquisite
detail, showing a segmented body and a
separate head,
as well as the exceptionally preserved
knots of nerves that run through both of
these structures.
But it was the structure of the nervous
system, however, that got scientists
most excited. Throughout the length of
the body, the nerves appear segmented,
feeding ladlike into each pair of the
animals legs.
But the concentration of nerves in the
head, the brain, appears very different.
It isn't segmented in the same way
leading the researchers to conclude that
it originated separately from the body
network.
[Music]
This in turn lends support to some of
the theoretical ideas for the role of
early nervous systems. It's conceivable
that the segmented network of nerves
throughout the body evolved to help
coordinate a novel abundance of legs
performing an action-shaping role.
Meanwhile, a separate knot of nerves
formed inside the head for processing
and responding to incoming sensations,
performing a sensory motor role, and
probably also exerting a kind of top-
down control like the brain of a
modern-day octopus.
And so it turns out half
billion-year-old carbon films tell us
much more than we can reasonably hope
for from such ancient long deadad
creatures.
But they can only go so far.
[Music]
The brains and nervous systems that they
preserve are already established enough
to show up in the fossil record.
They were early, primitive even. But
were they the first? Surely there must
be some even more simplistic knotted
nervous network that represents the very
first foray into electrochemical
control.
But where might we find them?
[Music]
Comparative anatomy can point us in the
right direction.
using modern-day descendants of each
animal group to tell us when the major
changes took place.
[Music]
Sponges are considered the most
primitive of all the animals, branching
onto their own line sometime between 800
and 700 million years ago.
And modern sponges have no nervous
system or brain to speak of.
[Music]
Next came the Nidarians about 740
million years ago whose living
descendants include corals and
jellyfish.
These animals have a network-like
nervous system but no brain that we
would recognize.
But after that the branching of the
animal tree becomes complicated.
So much happens in such a short period
of time at the beginning of the Cambrian
period with the vast majority of animal
body plans springing into existence in
the blink of a geological eye.
Indeed, we produced an entire
documentary on this incredible era that
you can watch after this one if you
missed it.
Animals like worms, arropons, molllesks,
echinoderms, and cordates all burst onto
the scene at once. And all of their
modern descendants have a brain.
It seems unlikely then the major
revolutions will lie somewhere along the
tangled knot of innovation that marked
the end of the protozoic and the
beginning of the phenorizoic some 550 or
600 million years ago.
The Ediaran period was in some ways a
warm-up for the Cambrian explosion,
but for the most part, the organisms of
the Ediakarine appeared to live quiet,
isolated lives. A lack of track marks
across or through the sea floor suggest
that they didn't move around much. And
even when many creatures are found
closely clustered together, there's
little evidence that they interacted
with one another.
[Music]
Indeed, on the vast majority of fossils
that have been found, there appear to be
no sensing organs like eyes or sensitive
probing tentacles.
With little movement and little external
input, these organisms wouldn't have had
much use for an expensive processing
center.
And yet, genetic evidence suggests that
the foundations of nervous systems had
already been laid down and had their
molecular underpinnings in place for a
100 million years by the time many of
the idiarans were gracing the seas.
It may be that these organisms were
simply developing their nervous systems
quietly in the background and that this
slowb burn was a necessary part of
building a successful multisellular
body.
Indeed, even relatively mundane life
processes like digestion, circulation,
and excretion needed to be coordinated
in entirely new ways when that life grew
bigger.
And it seems likely that internal
electrochemical signaling would have had
to have evolved in response, even if it
ended up leaving no trace in the fossil
record.
[Music]
And of course, there are some exceptions
to the rule of placid isolation among
idiocarons.
Some organisms like the mollisk-like
kimberella and the wormlike spraina have
a certain symmetry about their bodies
that suggest that they have a head as
well as being associated with trace
fossils that may be signs of their
movement through the seafloor sediments.
[Music]
If they crawled, slithered, or moved
with intention in any way, then they
must have had a nervous system of sorts,
acting in action-shaping mode to
coordinate that movement
andor in sensory motor to direct that
movement towards food and safety and
away from threats.
The interpretation of these fossils,
however, as well as their purported
behavior and their possible animal
affinities, is still in its infancy.
Right now, there's just too little
evidence to say whether these animals
really did move and respond to the world
around them.
[Music]
But then at the beginning of the
Cambrian period, everything changed.
And over the following 10 million years
or so, the seas were teeming with an
entirely different kind of life.
[Music]
The Cambrian explosion was not just a
radiation of new body shapes, but also a
sudden expansion of ecological
relationships and roles.
animals expanded into new territories,
no longer limited to the two-dimensional
world of the sea floor, but roaming down
into the soft sediments and swimming up
into the open water.
And with this new three-dimensional
territory came new opportunities for
food.
filter feeders, active grazers,
borrowing browsers, and apex predators
all moved about and interacted with one
another more than they ever had before.
With such complexity in the ecology,
there was suddenly a lot more to be
aware of, more things that it was worth
knowing about if a Cambrian animal hoped
to survive.
And the way to adapt to that complexity,
this need for information, was to
develop a nervous system that allowed a
timely and coordinated response.
Suddenly, it made a lot more sense to
have myriad sensing organs, new forms of
locomotion, and an electrochemical
processor to link the two.
Now, it made sense to have a brain.
[Music]
It was around this time that the first
complex eye appeared in animals like the
520 million-year-old arropod Fchania.
[Music]
This animal had a pair of eyes on mobile
stalks
like in the lobopods it shared the
oceans with. Scientists have found nerve
tissue connecting those eyes.
[Music]
The addition of eyes like these, which
were capable of depth perception and
looking at two directions at once,
contributed to the so-called Cambrian
information revolution,
which would have put pressure on
organisms to refine their neural
circuitry.
When more is known about the world
around you, decisions become more
complicated, and it's worth investing in
processing power to help make the right
one. Among
the remarkable radiation of new body
shapes that came during the Cambrian
explosion, there was one clear pattern
that emerged which can still be seen in
everything from earthworms to elephants.
That trend was for symmetry
and specifically bilateral symmetry
reflecting body parts down a central
line rather than some formless
construction of the less popular radial
symmetry favored by Nidarians like
jellyfish.
The billetarian body plan as it is known
is the major innovation on the branch
that leads away from sponges and corals
and in many ways enabled the ecological
revolution of the Cambrian explosion.
With a symmetrical body with muscles or
fins or loes or limbs reflected along a
central line, moving around becomes a
much simpler task.
reflecting down the middle also by
extension creates a front and back, a
forward and a backward, and an obvious
location for sensing organs.
Of course, none of this came about
accidentally, but would need to be
coordinated by a logical system of
nerves and a processor capable of
organizing inputs and outputs.
It created new opportunities for
action-shaping nervous systems, but also
required more sensory motor input than
ever before.
And all of this brings us to the first
brain on Earth.
At some point after our last common
ancestor with corals, a primitive animal
lived that was the first to experiment
and succeed with true bilateral
symmetry.
No fossils have ever been confirmed, but
scientists have speculatively named this
missing link the common ancestor of all
Bilotions,
an Bilotion.
Because of the way this animal must have
moved, sensed, and behaved, they would
have been the first to require a brain.
And it is in this animal that we would
find the most primitive brain of all.
Precisely when the Herbilaterian flexed
its newfound brain power is still open
for speculation.
It could have been as early as 570
million years ago.
It could be represented by or closely
related to the Idiacarans, Kimberella or
Spragina.
Or it could have taken longer to
assemble all the necessary parts. And
the Herbiliterian brain is still waiting
to be found among the fragmentaryary
fossils of the Cambrian explosions
opening act.
[Music]
It seems therefore that the
prerequisites for an animal brain are
somewhat unexpected.
It was only once animals had developed
muscles whose coordinated contraction
requires a fast signaling mechanism and
when they had evolved symmetry for the
coordination of those muscle
contractions to make any kind of sense
that the complexity and expense of a
brain became worth the effort.
Once brains were part of the animal
toolkit, however, no other animal hoping
to compete could afford to neglect them.
The larger and more complicated a body
grew and the more elaborate the
behavior, the more processing power was
needed.
[Music]
Most mollisks, including snails, clams,
and limpids, live slow lives.
Their fleshy bodies are protected by
shells.
Indeed, they have been since the first
shell appeared in the beginning of the
Cambrian.
And they move ponderously, or not at
all.
This is not the kind of behavior that
warrants investment in a big brain.
But seephalopods like squid, cuttlefish,
and octopus with their breakaway brain
success walked or floated their own
path.
After this group split from the other
mollisks 330 million years ago in the
Carboniferous, they went through their
own revolution of possibility and
necessity
200 million years after the evolution of
Botyions.
The sephalopods lost their protective
outer shell, making their bodies
simultaneously more flexible and more
vulnerable.
These animals were large enough to be
predators, but still small enough to be
prey to bigger creatures.
And this unique pressure from both sides
of the ecological pyramid made it
imperative that they coordinate
themselves and do it fast.
It's little wonder then that the
infinitely flexible octopus now seems to
stare back at us with a wisdom that far
exceeds that of its mlescan cousins.
[Music]
And so ultimately the evolution of the
brain was an inevitable part of the rise
of animals as an internal signaling and
processing center. Its presence went
handinhand with the ecological and
physiological leaps that allowed animals
to break onto the world's stage
and makes them what they are today.
Larger complex bodies and interactions
needed better control,
but also created more possibilities for
internal feedback.
At first for decision-making
and later for self-reflection and
contemplation that formed the basis of
the first minds.
[Music]
And yet today there is some evidence to
suggest that things are moving in the
opposite direction
as human brains become smaller.
The adult human brain today is at least
13% smaller than that of a homo sapien
that lived a 100,000 years ago.
Some have suggested that this is a sign
of our species mental decline,
caused by changes in the way that we
reproduce,
caused by changes in the way that we
live.
Complex societies allow for the less
intelligent members of a community to
survive and reproduce,
relying on their more intelligent peers
to keep them fed and healthy.
While before their lack of intellect
would have been their undoing.
If that is the case, we can only
speculate how long this decline will
continue,
especially with the continuing crutch of
technology to rely on.
But alternatively, the shrinking of
human brains may not reflect diminishing
mental powers at all,
but rather an ongoing structural change
to our brain tissues.
Indeed, we know from Phineas Gage's
example that the brain is constantly
changing its wiring and structure.
And it may be that over successive
generations, they are adapting to become
more efficient. doing everything we need
them to do with less physical material
cost.
Either way, whether we're honing or
merely whittling down our mental powers,
there isn't too much cause for alarm.
Until scientists can recreate the
billions of neurons and trillions of
connections that are needed to build a
full artificial brain and emergent
sentient mind, we won't be doing without
our 700 millionyear-old neurological
legacy anytime soon.