Ans. 1. As a result of industrial revolution, there was an increase in the level of pollution in Birmingham in England.
2. Owing to this, there was hardly any growth of algae or fungi on the tree trunks.
3. Instead, the tree trunks got covered by soot which gave them a black colour.
4. The black moths got camouflaged and began to get protection and the grey ones were easily detected by their predators and consumed by them.
5. Therefore, nowadays in the surroundings of Birmingham black moths are found in large numbers.