Read the given passage and answer the following questions:
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. Do you know that lichens can be used as industrial pollution indicators? They will not grow in areas that are polluted. Hence, moths that were able to camouflage themselves, i.e., hide in the background, survived. 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. Remember that no variant is completely wiped out. Similarly, excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. These are examples of evolution by anthropogenic action. This also tells us that evolution is not a directed process in the sense of determinism. It is a stochastic process based on chance events in nature and chance mutation in the organisms.
Why did white-winged moths survive before industrialisation?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Due to the presence of white-coloured lichen on tree trunks
The passage states that before industrialisation “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.” A white moth resting on white lichen was hard to see, so birds missed it. This hiding in the background is camouflage, and the passage says that moths able to camouflage themselves survived.
Option (1) Due to the presence of white-coloured lichen on tree trunks — Correct. The white lichen on the tree trunks gave the white moths a matching background. Predators could not pick them out easily, so more of them survived.
Option (2) Due to the dark tree trunks covered with industrial smoke and soot — Incorrect. Dark trunks covered with smoke and soot came after industrialisation. On such trunks the white moths stood out and did not survive.
Option (3) Due to the absence of predators in areas without industries — Incorrect. Predators were present before industrialisation too. The passage says the dark-coloured moths were picked out by predators; the white ones escaped only because they were hidden.
Option (4) Due to chance mutations that made them resistant to pollution — Incorrect. The passage links survival to camouflage, not to resistance to pollution. Before industrialisation there was no industrial pollution to resist.