Question

“Appearance of melanised moths post-industrialisation in England is a classic example of evolution by natural selection.” Explain.

Answer 1

Evolution by natural selection comes from England. In a collection of moths made in 1850s, i.e. before industrialisation set in, it was observed that there were more white-winged moths on trees than dark - winged or melanised moths. However, in the collection carried out from the same area, but after industrialisation i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed.
The explanation put forth for this observation was that ‘predators will spot a moth against a contrasting background’. During post- industrialisation period, the tree trunks became dark due to industrial smoke and soots. Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived. Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees- in that background the white winged moth survived but the dark - coloured moth were picked out by predators. Lichens can be used as industrial pollution indicators. They will not grow in areas that are polluted. Hence, moths that were able to camouflage themeselves, i.e., hide in the background, survived. This understranding is supported by the fact that in areas where industrialisation did not occur e.g., in rural areas, the count of melanic moths was low. This showed that in a mixed population, those that can better-adapt, survive and increase in population size. Remember that no variant is completely wiped out.