Kind: captions
Language: en
If you want to know if someone really
understands evolution, just ask them
this one weird question.
>> Why does poop smell bad?
>> Wow.
>> Oh gosh.
>> Because that's bacteria in it. I guess
>> microbiome. Probably trash.
>> Yeah, trash the body. The food we eat
because of the chemicals.
>> Arts don't always smell bad.
>> So,
>> yeah. Well, that's that's a different
question entirely.
>> Do you think it objectively smells bad?
>> M. Yes, I think so.
>> Yes.
>> How do you think it smells to flies?
Like [laughter] the
>> They like it. They like it.
>> Animals love stinky things.
>> Yeah,
>> they're attracted to it.
>> Poop smells good to flies because poop
is full of nutrients. They use it as
food. But it's also full of bacteria
that can be life-threatening to humans.
So, the real reason poop smelled bad to
us is because if anyone ever thought it
smelled good, they would probably get
really sick, die, and not pass on their
genes. After all, it's about survival of
the fittest. But survival of the
fittest? What? I mean, most people think
of natural selection as being about the
survival of the fittest individual
animal.
>> Individual.
>> Individuals.
>> Individual.
>> Animal.
>> Animal. Okay. So, it's like an
individual.
>> Yeah.
>> Which makes sense. [music] I mean,
individuals best adapted to their
environment have increased odds of
survival and therefore a higher
likelihood of passing on their genes.
So, it follows that each individual
should do everything it can to survive
and reproduce. That is, it should be
selfish. But if that's true, then how do
you explain this? I mean, worker bees
will sting predators to protect the
hive, even though it might kill them in
the process. Female worker ants are
sterile, so they can't reproduce. But
regardless, they work for the colony for
their entire lives until they die.
Monkeys adopt orphans. Wolves bring meat
to non-hunting members of the pack. And
squirrels can let out alarm calls to
warn others about nearby predators.
>> So if natural selection is all about
selfish individuals, why do we observe
so much altruism [music] in nature?
>> The survival is of the species that can
adapt.
>> It's generally the species
>> for the survival of the species.
>> So it's the survival of the species.
>> Okay.
>> But survival of the fittest species or
the fittest group also doesn't work. I
mean think about what you need for
natural selection to occur. You need
something that replicates itself many
times over, creating copies. And then
you need a pruning process whereby some
of those copies get eliminated and some
thrive to go on and create more copies.
The problem with groups or species as a
whole is that they don't typically make
copies of themselves. So you almost
never get copies of groups fighting
other copies of groups to see which
groups win out. So, if it's not survival
of the fittest individual and it's not
survival of the fittest group, then what
is it? Well, to explain that, I want to
take you on a little journey all the way
back to the beginnings of the earth.
Where we are now, there is nothing.
Well, not really nothing, but nothing
interesting. There are only simple
things like these blobs. This one might
be a carbon dioxide molecule or it might
be cyanide. We don't know for sure what
they are, but we do know that these
compounds are very simple. So, for now,
they'll just be blobs floating around
our void. In fact, much of what we'll
encounter along our journey here are
just hypotheses. A lot of Earth's early
history is still a mystery, so keep
[music] that in mind. Now, every so
often, our blobs get a surplus of
energy, maybe from a ray of UV light or
a nearby hot source. This is the first
major upgrade to our void, excess
energy, [music] as it allows our blobs
to interact with each other. Most of the
time, this interaction leads to nothing.
But sometimes, these blobs can combine
into more complicated compounds.
Here's a simple simulated example where
we only have four red blobs. Right now,
they are all individual particles. But
each time step we move forward, let's
say there's a 10% chance that all four
combine into one red mega blob. Now,
imagine this mega blob isn't very
stable. For every time step it's alive,
it has a 95% chance of falling apart
back into the four smaller blobs. If we
add more of these red blobs into the
mix, you'll notice that they rarely ever
come together. On average, a mega blob
only exists around 10% of the time. But
if we were to reduce the chances of the
mega blobs dissolving to only 1%, the
void would suddenly be filled with them.
This [music] fact hints at an important
law that governs our void. The law of
stability.
Unstable blobs fall apart and vanish.
Stable ones endure.
Now watch what happens if we speed this
up dramatically. Maybe a couple of years
per second. Maybe even a couple million.
You can see our blobs keep getting
random jolts of energy, so they combine
with others to form more complex
compounds.
Most attempts fail and fall apart. But
every so often, by pure chance, you get
a compound that is more stable than the
blobs it's made of. This doesn't happen
because the blobs want to build more
complex structures. It's just because
these new configurations happen to be
more favorable in the environment. And
now when these complicated compounds
become abundant enough, they too get a
chance to combine, making our void
increasingly complex.
And one day, by accident, this causes an
extremely unique shape to form, one with
a special property. See, the blobs it's
made of just happen to attract similar
blobs from the surrounding environment.
This red blob always attracts green
blobs, and this purple blob always
attracts yellow ones. And piece by
piece, all these blobs attract their
opposites until their counterparts
suddenly snap into position next to the
original shape. Now, this shape goes on
to do the same thing. Its green blobs
attract red ones and yellow ones attract
the purple until another shape yet again
snaps into position. This new shape
looks exactly like the original. What
just happened [music] fully
spontaneously is replication. One shape
became two. This marks the birth of the
first replicator.
We don't know exactly what this
replicator looked like. It might have
been a single standalone molecule or a
group of molecules that worked together
to replicate. [music] There's a lot of
debate on this today. So, instead, let's
represent the replicator as a character.
How about this one here? Perfect. Keep
in mind, it's still just a lifeless
molecule, one without any intent or
purpose.
Now, you might think that the chances
for the replicator to form were
extremely unlikely. But in our void,
where we have hundreds of millions of
years to play with, what might seem
impossible to us becomes virtually
inevitable. And the thing is, the
replicator only has to arise once. Once
it's here, it can take the simpler
compounds available in the environment
to copy itself at a much faster pace.
And so, it does that until it entirely
fills our void. At least that's what
you'd expect. But there is a flaw in the
process. See, during the replicator's
conquest of the void, one of its copies
makes a mistake.
Perhaps a stray ray of UV light hits it
during the replication process, or the
replicator uses a building block it
wasn't supposed to. As a result, what
we're left with is a new shape which is
slightly different from its parent, and
so its properties might be slightly
different, too.
This error might be harmful. For
example, it might make the copy less
stable. It could be beneficial, making
the copy better at replicating. Or it
could be neutral, not changing the
replicator in any meaningful way. This
marks the final milestone in our void,
mutation. Many species of replicators
now occupy the void. And what they do is
they replicate themselves. The problem
is they all need the same limited
resources. And so our void turns into a
battleground. So which replicator will
win? What kind of properties will the
void favor? Well, let's try to simulate
what happens.
Now, if you're looking to run your own
simulations or need a place to run your
own code, look no further than today's
sponsor, Hostinger. Say you wanted
[music] to keep track of everyday
science news. Manually filtering through
thousands of articles for the most
important or interesting stories would
be almost impossible. But Hostinger lets
you easily automate this process.
[music] You can use N8N, a platform that
lets you automate tasks, but you need a
place to host [music] it. And the
easiest, most cost-effective and secure
place to host NAN workflows is [music]
on a virtual private server or VPS from
Hostinger. It's like a powerful computer
you rent on the cloud. [music] So,
here's how you can create an article
scrubber. The workflow can grab every
new science article from a list of
portals. Then it can send the articles
to chat GPT to summarize their content.
And finally, you can add these quick
summaries to a board in notion. Using
Hostinger's pre-installed [music] NADN
template, the setup only takes one click
and you're good to start creating
workflows. [music]
By hosting NAD on a Hostinger VPS, you
get all the resources needed to run your
workflow [music] smoothly 24/7. Plus,
you can have unlimited workflows running
simultaneously. [music] Imagine the
things you could do and the time you
could save with automations on
Hostinger. They're having a Black Friday
sale right now. So, don't miss out. Scan
this QR code or [music] visit
hostinger.com/veritassiumnad
and use code veritassium to get an extra
discount [music] on top of this sale. I
want to thank Hostinger for sponsoring
this part of the video. And now back to
our simulation.
To simulate what a replicator battle
might look like, let's assign simplified
traits to each of the replicators.
Starting with the first one.
This replicator is special since it's
the only one that can form spontaneously
from smaller building blocks. So, we'll
give it a spawn rate. This should be
quite rare. So, let's set the chance of
formation to 1% per time [music] step.
Just keep in mind we're just making
these numbers up. The simulation is
purely illustrative. Now, once the
replicator spawns, let's say it's
governed by three key traits. First, a
death [music] rate. The chance of it
falling apart or being destroyed with
each time step. Let's set that to be say
2%. Second, a replication rate. The
chance to copy itself with each time
[music] step. Let's say 4%. And finally,
a mutation rate. The chance a copy comes
out mutated. [music] If it's 4%, roughly
1 in 25 copies will be a mutation. So
every time a new mutation spawns, it
will inherit the replication, death, and
mutation stats from its [music] parent,
but slightly randomized. Notice that we
won't give any of these secondary
replicators a spawn rate. They'll only
be able to form as mutations from
previous generations. So, if all of
their copies die out, they'll be gone
for good. Now, before we run the
simulation, I want to quickly shout out
the YouTube channel Primer. Our setup
was inspired by his amazing in-depth
simulations on evolutionary biology. You
should really check them out. Okay,
let's run it. [music]
The graph on the right will show how the
populations grow, and this box on the
left will show a slice of the void with
all the winning replicators [music] in
the correct ratios.
You can see how the first replicator
appears and then immediately disappears
because it just happened to die before
it got the chance to replicate. But
that's okay. The original replicator can
be created from smaller blobs, so it'll
come back at some point. This time, it's
starting to take off. You can also see
that it spawned some mutations, but
they're struggling to keep up.
Eventually though, superior mutations
pop up and start to replicate faster
than the original. But you can see
almost all of them are growing
exponentially, which is unrealistic.
That's because we're missing the final
piece of our simulation, limited
resources. The building blocks should
eventually run out. We can simulate this
effect by introducing a sort of [music]
resource factor to each species
replication rate. This factor should
depend on the total number of
replicators in the void [music] N which
we'll also divide with an arbitrary
crowding factor C. C lets us define the
maximum number of replicators we'll
allow into the void. Say C is [music]
10,000. Then once there are 10,000
replicators, the two terms cancel out
and drive the replication rate down to
zero. Meaning none of the replicators
will be able to make copies until the
population drops again. So let's see how
this changes our simulation. Okay, like
the last time, the original replicator
starts to grow, after which it's quickly
taken over by its mutations.
But this time, most of these mutation
populations start to decline.
Because of the scarce resources, the new
best population, the lime one, actually
starts stealing resources from the
others. After that, a few more mutations
pop up, even more powerful than [music]
the lime. Ultimately, the purple
replicator takes over, occupying around
9,000 of the 10,000 available spaces. It
completely curbs all the other
populations.
It goes without saying that the
environment plays a massive role in
which replicator wins. If you change the
environment, you likely change the
outcome. But let's look at the stats of
the replicator that came out on top this
time. That winning species has a
replication rate of 20% compared to the
17% average across all populations.
Obviously, being able to replicate
quickly pays off here. Its death rate is
below average. Replicators that fall
apart less quickly can make more copies.
And finally, it has a 1% mutation rate
compared to the average of 3.73%.
Although mutations help by injecting
diversity, for any single species, fewer
mutations mean more faithful copies.
If we rerun the simulation, you'll
notice the outcomes are always slightly
different. But the winning species
consistently have high replication and
low death and mutation [music] rates.
Now, in the real void, things wouldn't
have been as simple. Instead of just
tweaking these three stats, the
replicators would have to mutate all
sorts of different ways to gain an
advantage. For example, one replicator
might mutate a trait that lets it
destroy other individuals and then use
their building blocks to make more
copies of itself. This looks like
strategy, but it's really just chemistry
that gets copied over and over because
it helps the replicator survive.
Naturally, a risk of offense would
likely favor mutations that result in
defense. So, an opposing replicator
might stumble upon a mutation that helps
it form protective barriers from nearby
materials, letting it endure those
attacks. These barriers would also help
protect the fragile replicators from
environmental damage like UV light. This
marks an important threshold. The
replicator's traits aren't limited to
just determining the properties of the
molecules themselves. They can also
shape the environment. [music] So, by
chance, the replicators inevitably
mutate in ways that build scaffolding
around themselves to increase the
chances of their survival. [music]
They stumble upon ways of making
structures to propel themselves around.
They develop senses and ways of storing
energy. They even mix, exchange, and
steal traits from each other. Through
billions of years of [music] trial and
error, this scaffolding gets more and
more complex. And as a result, the
replicator's interactions with the void
become exceedingly indirect.
They build complex survival machines for
themselves. [music] Machines whose sole
purpose is to protect the replicators
inside. These machines became such
experts at surviving, they're still
around some 4 billion years later. They
are the bacteria, plants, fungi, and
animals [music] all around you.
Everything alive, including you, was
built as a survival vessel for these
[music] replicators. But today, you'd
barely recognize them as replicators.
Now, we just call them genes.
[music]
They're hidden deep within every living
creature. Strands of DNA made from the
sequences of A, T, G, and C nucleotides.
Now, one of the leading theories is that
those [music] earliest replicators were
actually something closer to RNA
molecules. But then over time, this must
have evolved into a more stable system
of storing information. The DNA and
proteins we use today. They are the code
that shapes our traits. We're taught
[music] that these traits are here
solely to help ensure our survival, the
survival of the individual or the
species. But do we [music] have this the
wrong way around?
>> When you have a child, what do you pass
on?
>> The DNA. Yeah, you know, yeah,
>> these tiny replicators are still
fighting the same battle that started
billions of years ago, and the logic
behind them hasn't changed. The traits
just become more convoluted. Replicators
that produce traits poorly suited to
their environment tend to become less
[music] common, while those that produce
advantageous traits become more numerous
in the population. So, it's [music] not
about the fittest individual or group.
It's fundamentally about the survival of
the fittest genes. They are the core
unit [music] of natural selection. But
why would natural selection care exactly
for the gene? Why not something smaller
or something bigger?
Well, for something to undergo
selection, it needs to have three
characteristics. First, it needs to be
able to make near identical copies of
itself. Second, it needs to exhibit
traits that affect its interaction with
the environment, which third affect the
probability of survival and reproduction
of the replicator. Something small like
a single nucleotide doesn't work because
sure it'll make identical copies of
itself, but alone it doesn't exhibit a
trait that could be selected for. What
about something bigger like a
chromosome? Well, each chromosome
affects potentially thousands of traits
that could influence its survival.
[music] But when most creatures
reproduce, sections of chromosomes get
swapped around. So a chromosome doesn't
stay together as a cohesive replicating
unit, and therefore it can't be selected
for. But a gene is somewhere in the
middle. It's a long enough stretch of
DNA that it can independently influence
a trait, but it's also short and stable
enough to be faithfully copied over into
future generations. This is why the gene
is the [music] unit of natural
selection. This perspective led to one
of the most powerful and controversial
ways of seeing evolution, one
popularized by Richard Dawkins in his
book, The Selfish Gene. Based on the
work of evolutionary biologists in the
1960s and 70s, and as a response against
the [music] then very popular group
selection theory, Dawkins argued that
just about every trait from animals
helping each other to being completely
selfish is a strategy that helps their
genes survive and replicate. Genes that
maximize their own survival are the
genes that propagate best, even if they
do [music] so at the expense of others.
Or in Dawkins words, we are survival
machines. Robot vehicles [music] blindly
programmed to preserve the selfish
molecules known as genes.
Now, you might think this framework
isn't all that groundbreaking. I mean,
take the emperor penguins in Antarctica,
for example. They hesitate to jump into
the water until they are sure there are
no seals around. So, what kind of genes
could help a penguin survive in this
environment? Well, if the penguin's set
of genes make it more likely to be
timid, the penguin might stay back until
someone braver tests the water. That
way, the penguin [music] is at a lower
risk of being eaten and has a better
chance of surviving, reproducing, and
passing on its timid genes. Here, you
can think about this either as the timid
genes help the penguin, or the penguin
helps the timid genes. Either way works.
So, is there any real benefit to viewing
things from the genes perspective? Well,
look at what happens when you use these
two frameworks to explain altruistic
behavior, which appears in a lot of
places in nature. Take California ground
squirrels for example. Females will let
out alarm calls if they spot a predator
like a fox or a hawk to warn other
nearby squirrels. [music]
Even though this puts her survival at
risk, the genes influencing this
behavior surely don't help this [music]
squirrel. But can the squirrel still
help the genes?
>> I think this is a bit more clear if you
think about the fact that most living
things reproduce [music]
sexually,
>> right?
>> So a squirrel will get half its DNA from
its mom and half from its dad. So it's
actually sharing half its genes [music]
with each parent, but also any child
that it has, it's also going to share
half of its genes with the child, but
also any siblings. But then if you take
a step out to an uncle or up to a
grandparent, then it's sharing one
quarter and then another step out is
1/8. All to say you share a lot of genes
with your immediate family. And
California ground squirrels, females in
particular, they live around family. So
if a squirrel has a set of genes that
make her call out when she spots a
[music] predator, there is a very good
chance that the squirrels that hear her
warning call also carry those genes.
Now, as a result of her alarm call,
let's say the squirrel attracts a
predator her way and it ends up getting
eaten. This action cost the call genes
the chance to pass themselves on to any
future offspring in [music] that
squirrel. But if the warning call saved
at least two copies of those genes in
two of the squirrels relatives, well,
then in total, these two [music]
squirrels have a better chance of
passing on the genes through their
offspring than that single squirrel did.
From the gene's perspective, this could
be [music] a good trade-off.
It doesn't matter which individual helps
the genes replicate, only that as many
copies as possible survive. This
principle that altruistically helping
your close relatives helps preserve your
own genes is known as [music] kin
selection. And the payoff behind any
altruistic gesture under kin selection
depends [music] heavily on how related
you are to the individuals you're
helping. Because the less related you
are, the smaller the chances that you
will share that particular gene with
another individual. And you [music] can
see this in nature. Male squirrels that
don't live near relatives almost never
give out warning calls.
Now, there is a big question this
gene-entric [music] view still has to
address. If selection really favors
genes that replicate well, then why
would sex ever evolve as a means of
replication if it throws away roughly
half the genes? Most animals reproduce
sexually, so why do it when some
organisms, like certain plants and
fungi, get to pass on all of their genes
through asexual reproduction? From a
genes perspective, this seems like a
much better deal. When it comes to
sexual reproduction, people like to say,
"Okay, well, it mixes up the genes. It's
like shuffling a deck of cards, and
isn't that better for creating more
variation?" And clearly, like, that's
advantageous. Another way this has been
explained is if the genes that regulate
sexual reproduction benefit from
replicating sexually, then they're going
to keep pushing for these genes, right?
>> Even if it's a net negative to all the
other genes in the genome.
>> Yeah.
>> So, if it benefits them, they'll keep
pushing for it. So, are there any
problems with how the selfish gene
explains natural selection? Well, yes. I
mean, it turns out the framework comes
with a lot of controversy.
One of the biggest criticisms against
the selfish gene is that it leaves
little [music] to chance. It implies
that every gene present in the genome is
there because it actively got selected
for by natural selection over many
generations.
But many genes are actually invisible
[music] to natural selection because
they don't really exhibit meaningful
traits in the population. Yet, they can
still evolve over time. Imagine 20 blind
cave fish, 10 with [music] green eyes
and 10 with blue. Since they're blind,
we'll assume that their eye color traits
make no difference to their survival.
So, they get passed down purely by
chance. Now, to form the next
generation, randomly pick any fish from
the first group and replicate [music]
it. If you repeat this 20 times, you get
a second generation. By chance alone,
one color will probably appear more
often than the other. And if you repeat
this process over and over many
generations, one color might eventually
completely take [music] over. That's not
because it's better, but purely due to
random sampling. This shift in the
frequency of gene variance is called
genetic drift. It's most apparent in
small populations and for traits that
aren't pruned by natural selection. But
it doesn't only apply to silent genes.
Even when genes exhibit meaningful
traits, there is a chance that genetic
drift overrides natural selection and a
less fit gene [music] will spread
through the population just by chance.
Look back at our replicator battle. If
we run our simulation enough times,
sometimes the winning gene won't be the
one with traits that maximize its own
survival. Here you can see that the
winning population actually has a higher
than average mutation rate just by
chance. [music] And the average mutation
rate is also higher than the starting
value. These are simplified examples,
but there is an ongoing [music] argument
about how much of evolution was actually
due to natural selection and how much of
it was up to chance. Another major
criticism of the selfish gene is about
the unavoidable implication behind the
word selfish. It seems to imply that
genes have agency, like they know what
they're doing and they understand the
consequences, but it's only a metaphor,
just as [music] portraying them as
characters was a way for us to make the
story more engaging. Of course,
molecules don't know what they're doing.
[music] They don't decide to replicate
or conspire to outco compete others.
They just react according to the laws of
physics. [music]
So what may look like intention is just
simple chemistry that happens to work
well and propagates. But perhaps the
most obvious and easiest to understand
criticism is that the whole framework is
an oversimplification. And that's true.
Genes are much more complicated than we
thought. It's not as simple as one gene
equals one trait. One gene can influence
many traits and one trait can be
influenced by many genes. There are
genes that are wholly contained within
other genes. There are genes that
inhibit or activate others. And then
there are even genes that seem to not
encode for anything. The so-called
non-oding DNA. All to say, we still have
a lot to learn about genes. Not to
mention that the environment itself,
like whether it's hot or cold or how
much food there is, also affects how
different genes get expressed. Genes are
much less deterministic than they might
seem. So, you might think that a single
gene would rarely have a large enough
effect that natural selection can
directly [music] impact it. But it
doesn't matter how convoluted the
pathway is. If a gene has a measurable
effect on its own survival and
replication, it will be subject to some
amount of natural selection. [music]
And surely the whole theory is a
simplification. But any theory or
framework of nature is. And what we're
covering in this video is an even more
simplified picture of that framework.
But that doesn't take away the fact that
viewing the world through this lens has
an incredible power to help us
understand the [music] process of
evolution. It helps us understand why we
see such a range of different behaviors
in our world because fundamentally those
traits tend to cause the increasing
prevalence of the genes they're
associated with. It's like [music] the
whole point is figure out what's true,
like get to the truth. And this to me
[music] is the baseline truth of
evolution is what I love about making
veritasium [music] is that we get to
sort of unpack and dig under the hood.
[music]
And it's what I loved about reading the
selfish gene book. So it really opened
my eyes to this. You know, previously
I'd always just probably thought at the
level of the individual, [music] but um
it [clears throat] makes more sense to
think at the level of the gene. The
feeling that you and every other living
organism is being driven by some
molecules deep in every cell is
fundamentally unsettling and seems
[music] to remove agency from you as a
as an acting thinking being in the
world. Yeah, it's pretty grim. But
whether or not you agree with the fact
[music]
that we might be controlled by our genes
and we're simply their [music] uh flesh
robots,
>> right?
>> I think it's kind of unreasonable and
unrealistic [music] to go through life
thinking that every decision is governed
by this. It doesn't really do you any
good cuz we perceive the world as
[music] as individuals. So I think it's
very beneficial to see yourself as as
your own thing, as your own, you know,
[music] unit.
I want to give a big shout out to Joe
Hansen from BS Smart [music] for helping
us out with this video and another shout
out to Primer for letting us adapt his
simulation on the first [music]
replicators. I have put links to their
channels down in the description, so
please check them out. And finally, I
want to say a huge shout out to you.
Thank you for [music] watching.