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.
Natural selection is based on certain observations which are factual. How many of the following are such factual observations?
A. Natural resources are limited.
B. Populations are stable in size except for seasonal fluctuation.
C. Members of a population vary in characteristics even though they look superficially similar.
D. In reality, population sizes grow exponentially as every member reproduces maximally.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Three
Darwin built natural selection on a few factual observations about populations. Together they mean that members of a population must compete for resources, and those with better heritable variations leave more progeny.
A. Natural resources are limited. — A factual observation.
B. Populations are stable in size except for seasonal fluctuation. — A factual observation.
C. Members of a population vary in characteristics even though they look superficially similar. — A factual observation; in fact no two individuals are alike.
D. In reality, population sizes grow exponentially as every member reproduces maximally. — Not a factual observation. A population would grow exponentially only theoretically, if everybody reproduced maximally. In reality population sizes are limited, and this gap is what leads to competition.
So three of the four are factual observations.
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.”