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.
The passage calls evolution a stochastic process based on chance mutation. Hugo de Vries, who believed mutation caused speciation, called a single-step large mutation:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Saltation
Hugo de Vries worked on the evening primrose. He saw large differences that arose suddenly in a population and called them mutations. He believed that mutation, and not the small heritable variations Darwin spoke of, causes evolution. Darwin's variations are small and directional, and evolution for Darwin was gradual. De Vries believed a new species could arise in one large step, and he called such a single-step large mutation saltation. Adaptive radiation, convergent evolution and the founder effect are different ideas: the spread of many forms from one ancestor, unrelated forms becoming alike for the same function, and a change in allele frequency when a few individuals start a new population.
NCERT Extract:
Mechanism of Evolution – “… Hugo deVries based on his work on evening primrose brought forth the idea of mutations – large difference arising suddenly in a population. He believed that it is mutation which causes evolution and not the minor variations (heritable) that Darwin talked about. Mutations are random and directionless while Darwinian variations are small and directional. Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation).”