- [Narrator] Thanks to brilliant
for supporting this video. If evolution is all about the survival and reproduction of the
fittest individuals, then why are creatures
sometimes nice to each other? (gentle music) In this video, we're
gonna build a simulation to start looking at the
biology of altruism. Certain genes will code for
certain types of behavior rules and we'll see which kinds of
work from a gene's perspective. So what do our sims look like? Each day blobs will go out to
the forest to eat some fruit. Each tree has enough
fruit to feed two blobs but some of the trees
have predators in them. If the blobs are unlucky enough to visit a tree with a
predator, they'll get eaten. But if they don't get eaten, they'll head to one of
the homes and reproduce, creating one or two new
blobs in their place. And then the cycle repeats. (gentle music) There's no altruism yet, but
let's make this a bit bigger and let it run for a
while to see how it goes. (light music) All right, so this little
ecosystem is mostly stable. Now let's add the
ability to be altruistic. When the blobs go to a
tree with a predator in it, one of them will notice the predator and it'll have two
options for how to react. The first option is to just run away, leaving the other blob to die. We'll call this the cowardly behavior. The second option will be
to make a bunch of noise and warn the other blob,
but in the process, attract the predator's attention with a 50% chance of
getting eaten afterward. Since these blobs are risking
themselves to help others, we'll call this the altruistic behavior. The blob's behavior will
be controlled by a gene which has two versions or alleles. The cowardly allele will be yellow and the altruism allele will be blue. Before we get to the simulation, it's worth saying that in real
life, behavior is determined by a mind-numbingly complex
interaction between many genes and the creature's environment over time, but this simple model is good enough to help us grasp some fundamental ideas. Okay, let's start with
equal numbers of each allele and see what happens. (light music) This graph shows the frequency
of each allele over time. At the beginning, half the alleles are
the blue altruism kind. And stacked on top, half the alleles are the
yellow cowardly kind. These values change over time but they always add up to 1 or 100%. And speaking of the change, it looks like the altruism
allele goes extinct after just a few generations. Maybe we made it a
little bit too dangerous to be altruistic, so let's
lower the death chance for being altruistic from 50% to 10% to see if the altruism allele
can do well on easy mode. (light music) Okay, it took a bit longer, but the altruism allele
still went extinct. Now you might think, "Hey, wait a minute. We only tried this once. Maybe it'll do better some of the time?" And yeah, that's a great point. So now let's repeat 30
versions of the same situation and see how that looks. Predict ahead of time what
you think will happen. Do you think the altruism
allele will always go extinct? Or maybe the first run was a fluke and the altruism a will actually increase in frequency more often than not? Our brains like to pretend
we knew things all along, so it's good learning and science practice to make a prediction
before you see a result. So, what do you think? Okay, there's a lot
going on in this graph. Each thin black line is one run and the thick black line is the average. In some runs, the altruism
allele lasted longer than others, but extinction seemed inevitable. Well, one did hang on
for all 400 generations but based on the other runs, it seems like it's pretty
doomed in the long run. So why did this version of altruism fail? Well, this is a computer simulation so we have a perfect record
for everything that happened. There were 225,817 blobs
saved by warning calls. 85,781 had the altruism allele and the other 140,036
have the cowardly wheel. And 24,151 of the altruistic blobs died after giving the warning. So overall, the altruistic
allele saved a net total of 61,630 copies of the
altruism allele, which is good. But since the total
population size is limited by the predators, the total number saved
isn't really what matters. More blobs being saved just results in more blobs getting eaten later on. What does matter though, is the
competition between alleles. A successful allele for altruism
would need to find a way to help itself more than
it helps its competitor. So how could we do that? Well, one way could be to let the altruism alleles see each other so they know who to help. But because DNA stays inside the blobs and it doesn't have eyes, we need some detectable feature
to go with the altruism. The classic example of
this is a green beard and that's a fun thing to put on the blob, so let's stick with that. So instead of the allele
for altruism from before, we have an allele for
green beard altruism. Now, when a blob with a green
beard notices a predator, it'll only warn the other blob if that blob also has a green beard. So let's see whether this
green beard strategy works in a simulation. And let's go back to the
50% chance of getting eaten after giving a warning. What do you think? Okay, that actually works pretty well. The green beard allele
drove the cowardly allele to extinction and decisively so. But again, we should
test it with many runs and with different settings. I ended up testing the 50% and a 90% chance of getting
eaten for 30 runs each. In each case, what do
you think will happen? All right, at the 50% death chance it seems like our first
run wasn't a fluke. The green beard allele does
indeed have a massive advantage. One of the runs got a pretty rough start but it still ended up
taking over before too long. At 90%, things are pretty noisy. Only 10% of the acts of altruism actually ended up saving an extra blob. So the random fluctuations
are pretty dominant. And even though the average
shows an upward trend, the green beard allele does
go extinct in several runs. After seeing these, I
was curious to try again but starting with only a 10% frequency for the green beard allele. Once again, what do you predict? Will the graphs look the same just shifted down to start at 10% or will something else look different? In the 50% case, there are a few interesting
things going on. After a while we see that the
average goes completely flat because in every simulation, one allele or the other has gone extinct. Of the 30 runs, 11 had the green beard
allele take over completely, and the other 19 had to go extinct. Even though the green beard
allele had an advantage and saw its frequency rise on average, it's still subject to the whims of luck when there are only a few copies, and once extinction
happens, it's permanent. It's interesting to imagine what kinds of alleles might've appeared in the history of the Earth
and could have done well but just got unlucky. The second interesting thing is that it seems like the green
beard allele's advantage depends on how many
green beards there are. Each run starts out with
mostly random wobbling, but when the density of
green beards gets higher the helping happens more often
and they get more benefit. And in the 90% death chance case, things are just really chaotic, but we still do see an
upward trend on average. All right, so we have a simple version of green beard altruism working, but we should check to see how it does when things are just a bit more complex. Remember when I said earlier that in real life behaviors are controlled by a complex interaction of many genes and the environment over time? Well, we're not gonna be able to capture all of that complexity here,
but we can at least notice that this one green beard
allele is doing kind of a lot. It doesn't just code for the
altruism toward green beards, which is complicated on its own, it also codes for the green beard itself. So as a small step toward
a more realistic scenario, let's split those parts
into two independent genes, each with two alleles. The first gene's alleles
code for a green beard or no green beard, and the other gene's
alleles code for altruism toward green beards or no altruism. And this means there will
be four types of creatures. The blobs with no beard and no
altruism will again be yellow and be called cowards. The blobs with no beard but altruism toward
green beers will be blue, and they'll be called suckers. The blobs with green beard but no altruism toward
green beards will be red and called impostors. And finally, the blobs with green beards who are also altruistic toward
green beards will be green and be called true beards. And it's worth clarifying that even though these bobs
are now different colors for tracking purposes, the blobs themselves can't see the colors they just see the beards. All right, to set up the next sim, we'll start with equal
numbers of all these types, and we'll go back to the 50% death chance. Also, this time, let's just skip ahead and run it 30 times and
look at the averages. But before we do, try
making one last prediction. (light music) Okay, in this case, showing all the lines from every run just gives us
this Jackson Pollock painting, so let's get rid of those lines and just look at the averages. So what happened? Well, the altruism allele gets
eliminated pretty quickly, whether it's paired with
the green beard or not. The first to go are the suckers. They help but they never get help. It's a tough world out there. The true beards do all
right at the very beginning, just like before, but they end
up going extinct in the end because they end up sacrificing themselves for the impostors. And the more impostors there are, the more a true beard is in
danger of sacrificing itself. And then there are the cowards that just kind of mind their own business. They don't do great, but once
the altruism allele is gone, there's really no difference between the impostor and the coward, so their relative frequencies
just bounce around randomly for the rest of the run. So it seems like green
beard altruism breaks down with even a tiny bit of complexity. And as we'd expect from this, we've only found a few examples in nature. They aren't literal
green beards, of course, but I've added some links to
some papers in the description in case you wanna learn more about them. All right, those are all the
systems we're gonna look at in this video. To be honest, I actually
find what we've seen so far to be a bit discouraging for
making sense of altruism, especially in humans. We only found one type that worked at all and it turned out to be
really fragile in theory and rare in reality. But don't despair, we have
a few more models to explore that are a bit more encouraging. And in the next video, we'll
talk about kin selection which follows Hamilton's rule. And while you wait for that video, why not level up your
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premium subscription, and in the process, help support Primer. As always, thanks for watching. (light music)
This is interesting, but I feel like it's fundamentally flawed. In the simulation imposters and suckers are 100% undetected by the true beards. True beards fail to save their altruistic but beardless fellows, but foolishly save the bearded imposters.
If we think about this as a real life village, you would have years and years of time getting to know what kind of person your fellow villagers are in non-lethal situations. Who is the person who never helps out? Who is the person who claims to be such a great guy, but in truth is a selfish coward? Who is the person who looks shady, but actually pretty stand up in a pinch?
Over the years, many imposters would be outed as selfish cowards, while many suckers would be vouched as altruistic. Certainly some imposters would out-wit the true beards, but true-beards who can see through the lies would know better and have a higher survival chance.
The suckers meanwhile I think might have a shot because the true beards know they have their back in a pinch. In fact a true-beard who can spot a sucker might have an evolutionary niche.
Perhaps this explains why humans love to gossip. Helps us discover the nature of a person and if we can trust them to have our back in a life-threatening situation. The upstanding priest caught cheating on his wife? Imposter! The sketchy looking neighbor who returned your friend's wallet? Sucker!
One thing I’d like to see tested here is the effect of altruism on cowards/impostors. In essence, if one of those allele combinations are saved by a sucker or true beard, they might be inspired to change themselves and help others. A type of “pay it forward” mentality, if you will.
Regardless, very cool video.
If anyone wants to actual lecture on this by someone who isn't a youtuber watch this Sapolsky lecture on intro to Behavioral Evolution, timestamped at the relevant segment.
This guy is unfortunately clickbaiting for a part 2 of their altruism models so I can't call this video outright garbage without knowing whether or not the companion piece corrects the errors in modeling.
I'll hold my judgement until the second part comes out, however, I think the practice of setting up a second part with a foundation of just outright bad science for clickbait is disturbing for a youtube channel dedicated to education. I think it makes it really easy for people to walk away misinformed.