Question

The figure given below shows white winged and dark winged moth present on a tree trunk with variable lichen growth (a) in unpolluted area and (b) in polluted area. Which variety of moth is likely to survive in these two conditions? Justify your answer.

Answer 1

• In a collection of moths in unpolluted area, more white-winged moths on trees would survive than dark-winged or melanised moths. However, in the polluted area, more dark-winged moths would survive i.e., the proportion will be reversed. 
• The predators will spot a moth against a contrasting background. In a polluted area, the tree trunks become dark due to industrial smoke and soot. Under this condition the white-winged moth cannot survive due to predators, dark-winged or melanised moth will survive. In unpolluted area, thick growth of almost whitecoloured lichen will cover the trees - in that background the white winged moth will survive but the dark-coloured moth will be picked out by predators. 
• Lichens cannot grow in areas that are polluted. Hence, moths that will be able to camouflage themselves, i.e., hide in the background, will survive. No variant will be completely wiped out. It is an example of process of Evolution by natural selection.