Read the passage given below and answer the following question.
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. The rate of appearance of new forms is linked to the life cycle or the life span. Microbes that divide fast have the ability to multiply and become millions of individuals within hours. A colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component. A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions. In due course of time this variant population outgrows the others and appears as new species. This would happen within days. For the same thing to happen in a fish or fowl would take millions of years as life spans of these animals are in years. Here we say that fitness of B is better than that of A under the new conditions. Nature selects for fitness.
Given below are two statements:
Statement I: When we describe the story of this world, we describe evolution as a process.
Statement II: When we describe the story of life on earth, we treat evolution as a consequence of a process called genetic drift.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is correct but Statement II is incorrect.
NCERT asks whether evolution is a process or the result of a process. The answer depends on which story we are telling: the story of the whole world, or the story of life on earth.
Statement I: When we describe the story of this world, we describe evolution as a process. — True. For the world as a whole, inanimate and animate, evolution is described as a process.
Statement II: When we describe the story of life on earth, we treat evolution as a consequence of a process called genetic drift. — False. For life on earth, evolution is treated as a consequence of natural selection. Genetic drift is only one of the factors that disturb Hardy-Weinberg equilibrium.
NCERT Extract:
Biological Evolution – “… Is evolution a process or the result of a process? The world we see, inanimate and animate, is only the success stories of evolution. When we describe the story of this world we describe evolution as a process. On the other hand when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection. We are still not very clear whether to regard evolution and natural selection as processes or end result of unknown processes.”