00:01
We're looking at the example of the speckled and black moths, and we're going to explain the process of natural selection.
00:08
So natural selection has two big requirements for you to remember.
00:13
The first requirement, number one, is heritable variation.
00:18
So you're looking at a population, and within this population, the individuals, they have different traits, and they pass these traits onto their offspring.
00:31
So this makes sense.
00:34
So in the case of our moffs, we're looking at a forest, and some of the moths are speckled, some of the moths are completely black.
00:51
And this is a genetic trait.
00:53
Black moths tend to have black offspring.
00:55
Speckled moths tend to have speckled offspring.
00:58
Okay, we have that.
00:59
Second requirement is we need differential reproductive success.
01:17
So what is differential reproductive success? it means that some individuals get to survive and reproduce more than others.
01:25
Some of these are going to have better chances of survival and reproduction.
01:29
And because the traits that decide whether or not they're getting to reproduce are heritable, it means that if, so starting off before the industrial revolution, these trees were silver, if birds have a harder time seeing these speckled moths, and they have an easier time seeing the black moths, these ones are going to get eaten, these will survive, reproduce, and you'll have more speckled moths in the next generation because of these two factors.
02:01
So this example here, we started out with step one, so this is in the pre -industrial times, and the speckled moths had the advantage.
02:20
So peppered moths, and this is what we call they were fitter.
02:27
So in evolution, when we say fitter, we mean better chances of survival and reproduction in that environment.
02:35
So what it means to be fit depends on the environment.
02:38
So when the tree is silver, the speckle moths are fitter...