Which of the following are the two key concepts of Darwinian Theory of Evolution?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Branching descent and natural selection
Darwin’s theory rests on two ideas. Branching descent means that all living forms share common ancestors and that lines of descent split again and again over time. Natural selection means that organisms better fitted to their environment survive and leave more offspring, so their inherited features spread.
Option (1) Natural selection and genetic drift — Incorrect. Natural selection is one of Darwin’s two concepts, but genetic drift is a change in allele frequency that happens by chance. It is one of the factors that disturb Hardy-Weinberg equilibrium, not a key concept of Darwin’s theory.
Option (2) Adaptive radiation and gene flow — Incorrect. Adaptive radiation is the evolution of different species in one geographical area from a single starting point, as in Darwin’s finches. Gene flow is the change in gene frequency caused by repeated gene migration between populations. Neither is one of the two key concepts.
Option (3) Branching descent and natural selection — Correct. Both terms of this option are Darwin’s own ideas. Branching descent accounts for the many forms that arose from common ancestors, and natural selection decides which of them survive and spread. Together, branching descent and natural selection are the two key concepts of the Darwinian theory of evolution.
Option (4) Branching descent and genetic drift — Incorrect. Branching descent is one of the two concepts, but genetic drift is a chance change in allele frequency studied under the Hardy-Weinberg principle. The second key concept is natural selection.
NCERT Extract:
Biological Evolution – “… 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. Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution (Figures 6.7 and 6.8).”