Predict how an extreme change in climate might affect natural selection in a species with little genetic variation.

If the specie can't change (using polar bears as an example) and the world gets excessively hot, they will die because they can only live in the cold because of their thick fur. The incapability of changing will cause them all to die because they can't handle the temperature. Polar bears can't just magically loose all their hair so they would probably go extinct if the temperature changed.