What factor controlled the population of peppered moths in england?

The evolution of the peppered moth evolutionary  instance of directional colour change in the moth population as a consequence of air pollution during the Industrial revolution .The frequency of dark-coloured moths increased at that time, an example of industrial mellaniam. Later, when pollution was reduced, the light-coloured form again predominated. Industrial melanism in the peppered moth  was an early test of Charles Darwin natural selection  in action, and remains as a classic example in the teaching of evolution.