Read the given passage carefully and answer the questions that follow:-
During his journey, Darwin went to Galapagos Islands. There he observed an amazing diversity of creatures. Of particular interest, small black birds later called Darwin's Finches amazed him. He realised that there were many varieties of finches in the same island. All the varieties, he conjectured, evolved on the island itself. From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches. This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation. Darwin’s finches represent one of the best examples of this phenomenon. Another example is Australian marsupials. A number of marsupials, each different from the other (Figure 6.6) evolved from an ancestral stock, but all within the Australian island continent. When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats), one can call this convergent evolution. Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be ‘similar’ to a corresponding marsupial (e.g., Placental wolf and Tasmanian wolf-marsupial). The essence of Darwinian theory about evolution is natural selection. Nature selects for fitness. One must remember that the so-called fitness is based on characteristics which are inherited. Hence, there must be a genetic basis for getting selected and to evolve. Another way of saying the same thing is that some organisms are better adapted to survive in an otherwise hostile environment. Adaptive ability is inherited. It has a genetic basis. Fitness is the end result of the ability to adapt and get selected by nature.
Given below are two statements:
Statement I: Analogy is accounted for by the idea of branching descent.
Statement II: Evolution by natural selection, in a true sense, would have started when cellular forms of life with differences in metabolic capability originated on earth.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Statement I is false but Statement II is true
Darwin’s theory rests on two ideas, branching descent and natural selection. Branching descent means that related groups arise from a common ancestor and branch apart, so it accounts for structures that share an ancestral plan.
Statement I: Analogy is accounted for by the idea of branching descent. — False. It is homology that is accounted for by branching descent, since homologous organs come from a common ancestor. Analogous organs arise by convergent evolution in unrelated groups.
Statement II: Evolution by natural selection, in a true sense, would have started when cellular forms of life with differences in metabolic capability originated on earth. — True. Natural selection needs variation to act upon, and among the first cellular forms this variation was in their metabolic capability.
Note: Statement I comes word for word from the chapter Summary, with one word changed. Summaries are short, so read them twice.
NCERT Extract:
Biological Evolution – “Evolution by natural selection, in a true sense would have started when cellular forms of life with differences in metabolic capability originated on earth. The essence of Darwinian theory about evolution is natural selection.”
Summary – “… Other phenomena like habitat fragmentation and genetic drift may accentuate these variations leading to appearance of new species and hence evolution. Homology is accounted for by the idea of branching descent. Study of comparative anatomy, fossils and comparative biochemistry provides evidence for evolution.”