Variation: Variation is when the offspring varies in his inheritable traits. The offspring will never be the same as the previous generation, it will have variations in color, size, etc. In this case a brown bear has two babies, one of them is brown and the other one in white.
Adaptation: This inheritable characteristics could be advantageous or disadvantageous. In this case, we can see how the brown bear is easy to see, so the seal could escape and the bear could die because of lack of food
In this case, the white fur of the bear is advantageous because it gives the bear a good camuflage in the polar environment, and it gives the bear good posibilities of getting food. It is more effective at the time of hunting
The individual with advantageous characteristics will have higer posibilities of reproducing, and its offspring probably will have the same advantageous characteristics.
Natural selection: All of this leads us to this point, natural selection occurs according to the environment, with inheritable variations that come from random mutations.
After thousands of years of natural selection and random mutations, this brown bears have become polar bears, with some new characteristics, like bigger paws, bigger size, and a diet change