In $1850s$, i.e., before industrialisation it was observed that there were more white-winged peppered moths (Bistonbetularia) on trees than dark-winged or melanised moths (Bistonca-rbonaria).

$\Rightarrow$ However, when 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.

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.

$\Rightarrow \quad$ Lichens can be used as industrial pollution indicators.

$\Rightarrow$ They will not grow in areas that are polluted.

$\Rightarrow$ During post-industrialisation period, the tree trunks became dark due to industrial smoke and soots.

$\Rightarrow$ Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived.

$\Rightarrow$ Hence, moths that were able to camouflage themselves, i.e., hide in the background, survived.

$\cdots$ This understanding 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