What is the connection between modern biology and the theory of evolution by natural selection

I’m not sure About natural selection but the relation of biology and evolution is the adaptation of other species through the years for example it has been a theory that the grizzly bear an black bear descended from the polar bear when a number of polar bears started living in warmer areas they had trouble living in there new environment because they were made for the cold but after many years of living there their offspring started to have different quality’s that made them more suitable to survive the environment like different colored fur and different claws this can be considered a form of evolution

Explanation:

d. organisms have cells with different shapes and functions.