When the Grand Canyon was forming, a population of squirrels were separated into two groups. The north side of the canyon is at a higher elevation and experiences more rainfall than the south side of the canyon. The two squirrel species you see here had a common ancestor, but over time, have evolved into two different species. How did natural selection lead to different species?

A) Because the squirrels were separated by the canyon, they were no longer able to reproduce and thus, became different species.
B) When the squirrels were separated, some of them acquired traits better suited for their new environment. This allowed them to survive and reproduce better than others. Over time, each group evolved to display unique traits for their different environments until one species evolved into two.
C) When the squirrels were separated, there was variation within each group. Some had traits that made them better suited for their home environment. This allowed them to survive and reproduce better than others. Over time, each group evolved to display unique traits for their different environments until one species evolved into two.
D) When the squirrels were separated, new mutations introduced variation within each group. Squirrels on each side of the canyon had different mutations. This allowed them to survive and reproduce better than others. Over time, each group evolved to display unique traits for their different environments until one species evolved into two.