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: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): There must be a genetic basis for an organism to get selected by nature and to evolve.
Reason (R): The so-called fitness of an organism is based on characteristics which are acquired during its lifetime.
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) → (A) is true but (R) is false.
Nature selects for fitness, and the fitness that counts is the kind that can be passed on to the next generation. A feature gained during one lifetime dies with the organism and cannot be selected over generations.
Assertion (A): There must be a genetic basis for an organism to get selected by nature and to evolve. — True. Adaptive ability is inherited and has a genetic basis. Only then can the fitter variant leave more progeny like itself.
Reason (R): The so-called fitness of an organism is based on characteristics which are acquired during its lifetime. — False. Fitness is based on characteristics which are inherited, not acquired. The idea of passing on acquired characters belongs to Lamarck, and NCERT says nobody believes it any more.
NCERT Extract:
Biological Evolution – “… Here we say that fitness of B is better than that of A under the new conditions. 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.”