Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Among the members of a natural population, there is competition for resources, and only some survive and grow at the cost of others.
Reason (R): Theoretically, population size will grow exponentially if everybody reproduced maximally, but population sizes in reality are limited.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A).
Darwin built natural selection on a few plain observations, and the work of Thomas Malthus on populations may have shaped his thinking. Two of these observations, put side by side, lead straight to competition.
Assertion (A): Among the members of a natural population, there is competition for resources, and only some survive and grow at the cost of others. — True. Natural resources are limited, so not every member can get enough. Only some survive and grow, while the others cannot flourish.
Reason (R): Theoretically, population size will grow exponentially if everybody reproduced maximally, but population sizes in reality are limited. — True. A growing bacterial population shows how fast numbers can rise. In nature, though, populations stay stable in size except for seasonal changes.
Why R explains A? If every member could produce so many offspring, numbers should shoot up. They do not, so most of the offspring must be failing to survive. The only way to account for this gap is a struggle for limited resources, in which some win at the cost of others. R is the very reasoning from which A follows, so R is the correct explanation of A.
NCERT Extract:
Biological Evolution – “… Natural selection is based on certain observations which are factual. For example, natural resources are limited, populations are stable in size except for seasonal fluctuation, members of a population vary in characteristics (infact no two individuals are alike) even though they look superficially similar, most of variations are inherited etc. The fact that theoretically population size will grow exponentially if everybody reproduced maximally (this fact can be seen in a growing bacterial population) and the fact that population sizes in reality are limited, means that there had been competition for resources. Only some survived and grew at the cost of others that could not flourish.”