Here's why:
* Evolution and natural selection can still occur in isolated groups. Even when groups are isolated, they can experience genetic variation and be subject to different selective pressures in their respective environments.
* Genetic drift: Isolation leads to genetic drift, a random process where allele frequencies change within a population over time. This can result in significant evolutionary changes, even without natural selection.
* Different selective pressures: Isolated groups may experience different environmental conditions, leading to different selective pressures that favor different traits. This can lead to divergent evolution, where the isolated groups evolve along distinct paths.
Example: Darwin's finches on the Galapagos Islands provide a clear example of this. Different islands had different food sources, leading to the evolution of distinct beak shapes among the finch populations on each island.
In summary, isolation does not stop evolution and natural selection. It often leads to different evolutionary paths, resulting in the diversification of life.