- [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)
