- [Justin] Survival of the Fittest. For many people, this phrase is synonymous with evolution. But we see in nature that sometimes creatures can act altruistically. Meaningfully hurting their own survival and reproduction chances to help others. In this video, we're gonna
built some simulations to get a better understanding of which kinds of
altruistic strategies work and which don't. (soft music) Alright, let's jump right
in with the simulation. We'll start with the world from the video on simulating natural selection. In this world, blob
creatures start each day at the edge of the world. In the morning, the food appears and the blobs go out to eat. The amount of food the blob finds before running out of
energy and returning home determines whether it dies, survives till the next day, or reproduces, passing its genes on to another creature, except that the genes might mutate. Now, let's get the creatures the ability to be altruistic. Here's how it'll work. If a blob creature
finds two pieces of food and still has energy left, it can take one of two routes. It can look out for
itself and its descendants by deciding to go home
early and reproduce, or it can be altruistic. Risking its guaranteed offspring to go and give a piece of food to another creature who hasn't eaten yet. And yeah, they regurgitated. Nature's gross. At the beginning of our simulation, half of the creatures will have a copy of an altruistic gene
causing them to be altruistic every time they get the chance and the other half of
creatures will have copies of a competing non-altruistic gene. When we let this simulation run, what do you think will happen? Would the selfish creatures take over or will the altruists
triumph through teamwork? Or maybe they'll stay mostly balanced. Pause here and make a prediction. Prediction made? All right. (soft music) Okay, well that was kind of sad. It turns out that unconditionally
sacrificing your offspring isn't a great long term strategy. So, how can we give the gene
for altruism a better shot? Well, what if we make acts of kindness a bit less punishing to
the altruistic creatures. Say, by letting the creatures
keep some reproduction chance when they give their food away. 50% instead of the previous 0%. So the cost of giving food away is half of an offspring on average. Maybe the food was already
partially digested. Again, nature's gross but ickiness aside, this makes the interaction net positive instead of just net neutral which is actually pretty
common in the real world. Okay, so let's restart our simulation with this lower cost altruism in place. Now what would you predict? Hmm. (light music) All right, it still doesn't work it seems. Remember that for a gene to be
successful in the long term, it needs it's copies to keep replicating. The problem with the gene for
purely unconditional altruism is that it helps copies of competing genes as much as it helps copies of itself and it's competitors
don't return the favor. So a successful gene
for altruistic behavior would need to find some way
of getting more help to itself than to it's competitors. Even if we're making nice creatures, the gene itself still needs to be selfish. How could a gene for altruism find a way to let it's copies
coordinate with each other. One way is to combine two different traits into the altruism gene. First, some kind of unique
outwardly detectable trait that can let the gene be recognized and second, the trait to be
altruistic toward creatures who have that detectable trait. So let's do that. Let's add an outwardly detectable trait to our altruistic creatures. The classic version of this is green beard and that's a fun thing to put on the blob, so let's stick with that. So the next simulation we'll try, we'll start out with half creatures that have the green beard gene who'll be altruistic
toward other creatures with green beards, and half creatures without green beards that will neither help nor get help. Again, pause to make a prediction. Are you convinced that the
green beards should do well or might there be another problem? Let's see. (light music) Cool. I was honestly a little bit worried before running these simulations that it still wouldn't work, but it does. Maybe you're not that
surprised and that's fine but even if you're not, this is still a pretty cool moment. We found at least one kind of gene that can crack natural
selection by causing creatures to put others before themselves, even if it's only sometimes. This is called inclusive fitness. The fitness includes all
the copies of the gene, not just the ones inside
a particular creature. Don't celebrate too much though because there's still a problem. Traits like green beard altruism aren't actually very common in nature. There are a few known cases, for example red fire ant colonies can have more than one competing queen. And apparently, the workers
can tell which queen shares her and sets of genes with them, and then they kill the
queens that don't match and help the queens that do match. That's cool and everything but there just aren't very
many examples like this. It turns out to be
pretty rare for one gene to code for two different traits that happen to work together so nicely. And even if that does happen, eventually, mutations could
produce multiple genes that each code for only one of the traits. So let's set up a simulation
to see how it looks when the traits are on separate genes. With the traits on separate genes, they're independent leading
to four possible combinations. The creature can have both, neither, just green beard or just
altruism towards green beards. Time to make another prediction. (light music) Okay, so as I kind of hinted
that before that simulation, the coordination between
copies of the altruism gene is broken and then the non-altruistic
creatures dominate. But hey, green beards are still cool. So, we've only gotten one kind
of altruism to work so far and it's a kind that depends
on a rare coincidence and doesn't appear much in nature. There's got to be something better, right? Well, in fact there is. It's known as kin altruism
or often kin selection. Instead of targeting
some outwardly detectable genetically determined trait, this kind of altruism
targets family members, whatever the traits may be. So, let's simulate one final
version of the altruism gene that causes creatures to be altruistic toward their direct parents
and direct children. Now the whole point of
this kind of altruism is that we can't see which
creatures have which genes. So this time, let's hide the graph and try to predict the results together while the simulation runs. The key concern with kin selection is that even close family
members aren't guaranteed to carry the same gene. So the altruism gene
has to do some gambling. For any kind of gambling strategy to work while in the long run, the cost of playing needs
to be lower than the payoff for a win times the chance
that you actually win. Right? The average payoff needs
to be higher than the cost. In the context of kin selection, you'll hear this called "Hamilton's Rule." Looking at this simulation and thinking of the altruism
gene as the gambler, the 5% mutation chance means that there's a 95% chance that parents and children
share the same version of the altruism gene. So that's our chance of winning. The cost of being altruistic
as we decided before is half of an offspring on average and the benefit to a
creature who receives food is one since that food
is converted directly into offspring. These numbers aren't exact
since both creatures involved do have other chances to get food but this should get us pretty close. And comparing, the
expected payout is almost twice the cost, so even with the inexact
cost in payoff numbers, it seems pretty clear
that the altruism gene is gonna do well here. And this is where I realized that altruism is an illusion and my heart descended into darkness only for a little bit though. Once I dug in, collected some
data on what was happening and found more precise numbers
for the cost and benefit, I figured out what was wrong. It's that Hamilton's Rule is a lie! Which I'm sorry to say is
gonna require it's own video. But for now, suffice it to say that by lowering the cost
of the altruistic act, and cranking up the likelihood of winning by lowering the mutation chance, we can find a set-up where
a gene for kin selection tends to flourish. This is the kind of altruism we see all over the place in nature from parents caring for their young to sterile worker bees helping the queen, conclusive fitness can
be naturally selected. All right we spent a
lot of time in the weeds in this video, so before we go, let's
not remind ourselves of the difference between
a creature and it's genes. The genes involved in
altruism are still selfish. The only ones that survive are the ones that are able to coordinate their own copies. But this does not mean the
creatures themselves are selfish. They genuinely care
about and make sacrifices for each other, whether it's because they're family or because they just can't
resist the look of a green beard. See you next time. Hey, thanks for watching. If you enjoy this video and
wanna support more of them, you can help by subscribing, sharing with someone else who you think might also like video, or if you're so inclined by
supporting directly on Patreon. In any case, thanks again. (light music)
Cool youtube channel, now this is why I love reddit!
I've been fascinated lately by WD Hamilton's work on altruism. Hamilton proposed that altruism arises when it provides a survival benefit to close kin. What's weird is that human beings show altruistic behavior when it's not close kin (think of fire fighters, police, soldiers), and I'm wondering how this happens, and what would make this stop happening. What about the Free Rider Problem?
Altruism is a product of natural selection. These are not opposites, and anyone trained in biology knows that altruism is just an extension of selfishness. Nevertheless, nice video.
Altruism is sexy