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- [Justin] The term the selfish gene has seen
its share of confusion and controversy.
On its face, it seems like it might be saying
that biology destines us to be selfish.
And also, the author of the book popularizing it,
well, to use his own words, he's not much of a diplomat.
To try to overcome some of that baggage,
we're gonna take it slow and analyze this term,
selfish gene, in three parts.
In the first part, we'll work up a definition
of the word gene so we can agree on exactly
what it is we're calling selfish.
In the second part, we'll look at what kinds
of strategies a successful gene might have.
Spoiler alert, not all the strategies end up
producing creatures that are selfish.
And that's actually where this video will end.
The third part will consist of follow-on
videos that dive deeply into each kind
of strategy, using simulations to understand
when and why that strategy can work.
In previous videos, we're been dealing
with creates that replicate and make
exact copies of themselves,
except for the occasional copying mistake,
which we call the mutation,
most real creatures don't actually
work this way, though.
The way biology happens to work,
creatures are built and maintained through
complex chemical processes which all
follow the information encoded in a kind
of molecule called deoxyribonucleic acid,
or DNA for short.
When creatures reproduce sexually,
which most animals and many other organisms do,
they produce offspring with a mixture
of DNA from their parents.
And, even single-celled organisms that do
reproduce with only one parent often have
some way of swapping DNA with each other.
So creatures don't truly replicate
because their descendants aren't identical copies.
They have different DNA.
The sections of DNA are what actually replicate.
So that's DNA, but what is a gene?
We're gonna use the simple definition that
a gene is a section of DNA that lives
inside a creature and determines one trait.
And any creature has many genes,
which, together, determine all of its traits.
This is close to the definition of a gene
we got from Gregor Mendel, who's often called
the father of modern genetics.
Before moving ahead with this definition,
we should admit that our current understanding
of how DNA affects traits is massively
more complicated than this.
Many creatures actually have two versions
of each gene, which Mendel did know.
Also, one gene can affect several traits.
And, most traits are affected by several genes.
And different genes can affect how others work.
And, one section of DNA can be read
in multiple ways.
And, it's all mediated by multi-step chemical processes.
And it also depends on the environment inside
and outside the body, and on timing.
So, yeah, it's a big mess.
So if you find yourself making a simple
cause and affect argument about the genetics
of any particular trait, especially in humans,
you should be careful, because it's probably
more complicated than you realize.
But with all that said, our simple definition
will make it easier to think about some
basic principles, which still apply in
the more complicated reality.
And our definition needs one final tweak.
A gene isn't really a physical chunk of DNA.
It's actually a pattern of DNA that can exist
in many copies, which might be in several
bodies at once or over time.
So, while the creature only lives once,
a gene is potentially immortal.
In the long term, competition is only between genes.
So genes are the units of biological natural selection.
This really is the key idea in this video.
Genes are the units of natural selection.
So, if you imagine yourself as a gene
who somehow has feelings and makes plans,
what kinds of strategies could make you
successful in this competition between genes?
Well, the most obvious strategy is to make
your creatures really good at surviving and reproducing,
even at the expense of other creatures
who might carry competing genes.
This could mean your creatures are actively selfish,
say, by stealing from others,
or they might just be doing the best they can,
happening to squeeze out other creatures.
We saw an example of this in the natural selection video.
When faster, less efficient creatures were
allowed to appear, they took over the population,
even though the total number of creatures
suffered for it.
Things don't have to be so grim, though.
Genes can also be successful by coding
for behaviors that are good for the carriers
and also for other creatures.
This category includes simple strategies
like passivism, where creatures can tend
to give up some resource to avoid a costly fight
that might injure or even kill them.
And it includes a more complex kind of behavior
called reciprocal altruism,
where creatures help each other with the expectation
of getting help in return.
The mystery here is why these strategies
aren't just beaten by cheating strategies
who just take advantage of the kindness
without being kind themselves.
The last category is also the most
counter-intuitive at first,
or at least it was for me.
It's possible for a gene to have a successful
strategy where its carriers help others
by acting against their own self-interest.
Unlike in reciprocal altruism,
these creatures hurt their own reproductive chances
without needing to get anything in return.
They're just plain altruistic.
This can be a good strategy, because copies of
the gene can exist in more than one individual
at a time.
From the gene's perspective, it doesn't matter
which copies reproduce.
So sacrificing one copy for the good
of the group can work out just fine.
One term for this is inclusive fitness.
The mystery here is how a gene can make sure
it tends to help its own copies rather than
copies of competing genes.
We'll dive into the mysteries of the second
and third categories in future videos.
But looking at this chart as a whole,
we can see that, even though a gene's effect
can be good for individual carriers
or whole populations, neither of those are
requirements for a gene to be successful.
This is because of that key idea that genes
are the units of natural selection,
not creatures, not populations, just the genes.
The only thing that consistently matters
to all genes is that their copies replicate.
What a bunch of dicks, right?
(light music)