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 moth study in the passage is one evidence for evolution. Another comes from comparative anatomy: the thorn of Bougainvillea and the tendril of Cucurbita represent:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Homology
Comparative anatomy compares the body parts of different organisms. Homologous organs have the same basic structure and origin but are used for different jobs, because they developed along different directions to meet different needs. This is divergent evolution, and homology points to common ancestry. The thorn of Bougainvillea protects the plant, while the tendril of Cucurbita helps it climb. They share the same basic structure, so they are homologous.
Option (1) Analogy — Incorrect. Analogy is the opposite case: organs that look alike and do the same job but differ in structure and origin, such as the wings of a butterfly and of a bird. A thorn and a tendril do different jobs, so they are not analogous.
Option (2) Convergent evolution — Incorrect. Convergent evolution produces analogous organs: different structures evolve for the same function. It does not fit a thorn and a tendril, which share a structure but differ in function.
Option (3) Homology — Correct. The thorn and the tendril have the same basic structure but different functions. This is homology, which comes from divergent evolution.
Option (4) Adaptive radiation — Incorrect. Adaptive radiation is the evolution of many different forms from one ancestral form spreading into new habitats, as in Darwin's finches. It describes a whole group of species, not a pair of organs.
NCERT Extract:
What are the Evidences for Evolution? – “… Hence, in these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry. Other examples are vertebrate hearts or brains. In plants also, the thorn and tendrils of Bougainvillea and Cucurbita represent homology (Figure 6.3a). Homology is based on divergent evolution whereas analogy refers to a situation exactly opposite.”
Figure 6.3 Example of homologous organs in (a) Plants