Evolution doesn't always happen slowly. To take a well-known example: The lactase persistence gene went from insignificant levels to covering the majority of Europe and northern Asia over just a few thousand years.
Evolution usually happens slowly because usually species are already well-adapted to their environment. When an environment changes to provide a significant benefit to a particular mutation, the spread of that mutation can speed up dramatically.
Evolution usually happens slowly because usually species are already well-adapted to their environment. When an environment changes to provide a significant benefit to a particular mutation, the spread of that mutation can speed up dramatically.