#1 Genetic variation: In the worm population there are two types of polar bears , the ones that are born with thick skin and the ones that are born with thin skin .
#2 Overproduction and struggle for survival: The polar bears that have thin fur have a better chance of not surviving because of the cold weather in there environment, the polar bear with thin fur doesn't have enough fur to keep it warm which may cause the polar bear to die. The polar bears with thick fur have a better chance of surviving the cold weather in there environment.
Differential survival and reproduction: Since the polar bears with thick fur have a better chance of surviving , they can finding a mate and reproduce. The polar bear will then pass on the trait of thick fur and produce a thick fur polar bear that can survive in the environment.
Change in the gene pool: Since more thick fur polar bears are surviving and reproducing, you will see an increase in thick fur polar bears in the polar bear population. You will also see a decrease in the thin fur polar bears since they cant survive the weather in there environment and are less likely to reproduce.