An example of natural selection and adaptation is the creation of polar bears, which is believed to have evolved from brown bears.
During a point in time when Eurasia was covered in glaciers and the Arctic Ocean was frozen, it is believed that a group of brown bears in the north split off from their ancestors in search of food.
The bears attempted to hunt for food, but they couldn't blend into the snow and were noticed by their prey.
Eventually, a mutation arose which allowed the bears to blend into the white snow around them.
Bears without white fur usually starved to death due to being unable to hunt and catch prey, so bears with the gene reproduced more. As a result, the number of bears with white fur increased over time.
Polar bears evolved as a result of natural selection in which bears with white fur were more adapted and suited to the snowy environment and were the "fittest".