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Lichen
Another interesting observation supporting 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 soot. 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.
(i) Why are lichens called pollution indicators?(ii) Which moth population was high before industrialisation in England?(iii) What changes take place in the population of melanised and non melanised moth after industrialisation?(iv) After industrialisation, population of which moth was found to be higher?

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