This example is about the peppered moths. Let's take a look. It says industrial melanism in the peppered moths is one of the classic examples of evolution by natural selection. I just want to pause right here. This is one of the classic examples.

This is something you've likely heard about before, and if not, I definitely recommend you'd be familiar with this story. Alright. Let's keep going. It says at the start of the 1800s, almost all moths were light colored with small dark spots, which allowed them to camouflage on the lichen of trees. During the industrial revolution in the mid to late 1800s, much of London and surrounding areas were covered with a layer of black soot.

By the 1900s, most moths were fully black colored. Today, the population again is composed of mostly light colored moths. Based on this evidence, answer the questions below. Alright. Before we answer the questions, let's just look at the image here.

So here we see a dark background, sort of that soot colored background, and here you see that light colored moth really being very visible on it. And this dark colored moth right there, very hard to see. Now on this light colored lichen background here, the light colored moth, very hard to see. The dark colored moth, very easy to see. Alright.

So now that we have that background, let's see these questions. The first question here, what variation did natural selection act upon? Remember natural selection can only act if there is variation in the population. So what was the variation we're talking about? Alright, should be pretty straightforward here.

It's just talking about the light versus dark coloring, I'll say. Alright. Next, it says in the early 1800s, what variant had higher fitness? How do you know? Alright.

Well, what do you think? Which variant in the early 1800s had higher fitness? Well, it says here at the start of the 1800s, almost all moths were light colored. Alright. Well, that seems that the light colored moths probably had higher fitness at that time.

Right? If they're very common, it's likely because they are surviving and reproducing better and that's our definition of fitness. So light, I'm just going to say they're more common and we can assume why that would be, right? In the start of the 1800s, there wasn't black soot everywhere. There was this lichen on the trees, and so they were better able to survive because they're better camouflaged.

Alright, in the late 1800s, which moths had higher fitness? Well, in the late 1800s, it says here by the 1900s most moths were almost fully black colored. So that means in the late 1800s, those black colored moths were reproducing more. They have higher fitness. So I'm going to say the dark colored moths have higher fitness then, and again it's because this population is changing to become dark colored and sort of that's our definition of fitness, they're surviving and reproducing more.

So finally, why do you think the light colored moth is again more common today? Well, I don't know if you've been to London, but it's not covered in black soot. Okay? So the environment, is no longer dark colored. Right?

So remember fitness depends on the environment and when the environment changes fitness changes. So when there's a dark layer of soot everywhere, everything's black and grimy. It's advantageous. You have higher fitness to be a dark colored moth. When that soot goes away and lichen comes back, it's light again, well, fitness changes.

Now the light colored moths are more common again, and that's natural selection. Alright. More practice after this. Give it a try.