Mutations provide the vital raw material for natural selection, so if the mutation rate is too low a population will not be able to evolve fast enough to keep up with environmental changes.

• 公孔雀大且华丽的尾巴也许会吸引母孔雀的注意力，但是拖着条沉重又惹眼的花尾巴降低了他们的生存机会。