UPSC Prelims 2002 Q11: Science & Technology – Biology
Among living organisms,
which one of the following is the most responsible factor for bringing about the origin of a new
species?
- (a) Isolation
- (b) Mutation
- (c) Natural Selection
- (d) Sexual Reproduction
Answer: (a) Isolation
Explanation
Factor most responsible for the origin of a new species
| Factor | Role in evolution |
|---|---|
| Isolation | Geographical or reproductive barriers stop gene flow, so populations diverge into new species |
| Mutation | Supplies new variation, but does not by itself separate populations |
| Natural selection | Favours adaptive traits within a population |
| Sexual reproduction | Recombines existing variation |
Speciation needs the gene pools to be separated. Isolation (geographical, ecological or reproductive) prevents interbreeding, and then mutation and selection act independently on each group until they become distinct species. Hence isolation is the most responsible factor for the origin of a new species.
Answer: (a) Isolation.
Why each option is right or wrong
- (a) CORRECT. Isolation separates gene pools and leads to a new species.
- (b) Incorrect. Mutation provides variation but not the separation.
- (c) Incorrect. Natural selection acts on variation within a population.
- (d) Incorrect. Sexual reproduction only shuffles existing genes.
Key point
Speciation = isolation + variation + selection; isolation is the decisive step.
Remember
No isolation, no new species.
Common mistakes
- Choosing mutation, the source of raw variation.
- Treating natural selection as the same thing as speciation.
- Forgetting that gene flow keeps populations together.
Exam tip
Ask what stops interbreeding: that is isolation.
Sources
- NCERT Class XII Biology — Evolution
- Ernst Mayr — Systematics and the Origin of Species (Columbia University Press, 1942)