In case of peppered moths, pale and dark moths are observed. Pale variety is known to be the wild type variety. During industrial revolution, industrial melanism led to prevalence of dark variety around the cities and pale variety continued to be in majority in areas away from the industries. After enforcement of regulations for controlling pollution, reappearance of pale moths in majority was observed around cities again. Driving force(s) for these adaptive changes is/are:
i. Increased pollution around industries
ii. A stable transposition of a gene in moths
iii. Limitations of the vision of birds to differentiate dark moths on darkened barks and pale moths in presence of lichens
iv. Ability of lichens to grow on barks in less polluted areas only.