Name: Simulating Natural Selection
Uploaded: 2025-11-19T01:58:15.000Z
Duration: 10 min
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

If you've watched the previous videos in this series, you've seen these blob creatures live, die, and replicate.

We just gave each type of creature a replication chance and a death chance.

And we saw what happened with natural selection, though, we usually can't know precise replication and death chances.

Instead, selection comes from interactions between a creature's traits and its environment.

So in this video, we're going to make a real evolving system by putting our blob creatures into a simple environment and giving them traits.

Let's see what we can learn by watching some actual natural selection happen.

Alright, so what does our environment look like?

And each morning, food appears on the plane, and

the blobs emerge from their homes around the edge to go out and eat the food.

If a blob fails to find any food before running out of energy, it will die.

If a blob gets one piece of food and manages to get back home to the edge, it will live on to the next day.

And if a blob gets two pieces and gets home, it will survive to the next day and also replicate, adding another creature to the next day.

Before we talk about a creature's traits and how they might vary, let's just watch these creatures live their lives for a few generations.

So we see that these creatures can manage to live over several generations in this environment.

And the number of creatures actually expanded over the first few days and then leveled off.

So the population started out below the carrying capacity.

But once the population expanded to around 95, the creatures really had to compete with each other for food.

Once we allow mutations, the variation will give some creatures an advantage, and

we'll start seeing some natural selection of traits.

So let's turn on mutations and see what happens.

Each time a creature replicates, there's a chance that a mutation will give the new creature a slightly lower or slightly higher speed.

Speed is great because it allows you to beat other creatures to the food.

If a creature's speed is doubled, it will cover a distance in half the time, but

use twice as much energy to go that distance faster.

Creatures can't forage over as much ground as slower creatures, so they might not find food before running out of energy.

If we unpause this world with speed mutations turned on, what would you predict when the faster creatures start appearing.

Or will the slower creatures prove the virtue of patience?

It could also turn out that the current creatures have struck a good balance.

Or it could be that being fast and being slow are both good strategies.

We'll just have to unpause and see what the nature of the situation is.

And let's speed it up a bit so we can see more generations.

Alright, so it turns out to be worth sacrificing efficiency for speed in this environment.

Or at least the initial speed value I picked was slower than optimal.

This is our first example of natural selection.

We didn't know the best speed value going in, but

the creatures mutated and somewhat randomly tried out different speed values.

And then through natural selection, the population evolved to have a higher average speed over time.

And I want to double down on that last point.

As much as we all love Pokemon, individuals don't evolve in the biological sense of the word.

One interesting thing to notice is that as the average speed of the population went up, the number of creatures in any given day tended to go down.

The creatures now compete more fiercely and are less efficient overall.

This is part of the meaning of the term selfish gene.

We'll talk more about genes and the term selfish gene in future videos.

But for now, just notice that even though we might call these creatures better because they did better in the competition for survival, the total population size actually went down.

Selection didn't happen for the good of the species as a whole.

But again, more on that in future videos.

Alright, now that we've gotten our feet wet with one varying trait, let's add two.

Size scales the creature in all three dimensions.

The benefit of size is that it lets you eat other creatures if you're at least 20% larger than them.

Getting an extra food source is great if you can pull it off.

The energy cost depends on the cube of a creature's size value.

I could have picked any function for the energy cost, I suppose, but I made it a cube.

Because volume scales as the cube of length, and

volume is closely linked to the mass a creature has to carry around.

The total energy cost of a creature's movement.

Each time step is equal to the cube of the creature's size times the square of the creature's speed from before, which you might notice is reminiscent of the formula for kinetic energy.

But anyway, it's especially costly to be both big and fast.

And on top of this cost, smaller creatures will actually run from creatures big enough to eat them.

So to benefit from being big, you need at least some speed.

Long story short, being big is high risk and high reward.

Each creature has a certain sensing distance at which it can sense food or other creatures.

Once a creature sees food or a smaller creature, it can move straight toward it.

Or if it sees a bigger creature, it can run away.

This sensing distance gets larger as a creature's sense trait goes up, allowing it to avoid danger and be more efficient with its movements.

Each time step, a creature pays a movement energy cost, which depends on its size and speed, and

a sensing energy cost, which is just equal to its sense trait.

Alright, so now that we have three traits, let's rewind to before we turned on speed mutations and instead turn on mutations for all three traits.

To keep track of what's happening to all three traits at once, we're going to use this three dimensional graph.

Each dot in the graph represents one creature, and

the position of the dot depends on the speed, size and sense values for that creature.

The first thing I notice is that the average speed is significantly different from what it was when only speed was allowed to vary.

Which is a little bit surprising because we didn't explicitly change anything about how speed works.

But with sense and size able to vary, different creatures were able to appear.

A creature's environment includes all the creatures around it, and

for whatever reason, speed just wasn't as valuable this time around.

When I first ran the simulation, I thought there would be a pretty intense selection toward creatures with higher sense, because sense informs everything else the creature does, and

But instead, sense is fairly spread out and centered roughly around the starting value.

That's the thing about natural selection.

It doesn't care what I or anyone else thinks is best.

Subtitles ListPlay Video

Simulating Natural Selection

apparently

trait

slightly

thrive