UPSC Prelims 2002 Q43: Science & Technology – Biology
In the context of the organic evolution, the loss of limbs of snakes is explained by the
phenomenon of
- (a) use and disuse of organs
- (b) adaptation to living in burrows
- (c) natural selection
- (d) inheritance of acquired characters
Answer: (a) use and disuse of organs
Explanation
Loss of limbs of snakes in organic evolution
| Theory | Explanation of limblessness |
|---|---|
| Use and disuse of organs (Lamarck) | Limbs not used while crawling gradually became reduced and were lost |
| Inheritance of acquired characters (Lamarck) | The reduced condition was passed on to offspring |
| Natural selection (Darwin) | Favoured the limbless forms for burrowing |
| Adaptation to burrows | A description of the habitat, not a mechanism |
In the Lamarckian reading, which this question follows, the loss of limbs in snakes is explained by the use and disuse of organs: organs that are not used degenerate over generations. Modern biology explains it through natural selection and developmental gene changes, but among the options the phenomenon that the paper intends is use and disuse.
Answer: (a) use and disuse of organs.
Why each option is right or wrong
- (a) CORRECT. Disuse of limbs explains their loss in the Lamarckian view.
- (b) Incorrect. Adaptation to burrows describes the habitat rather than a phenomenon of evolution.
- (c) Incorrect. Natural selection is the Darwinian process, not the one the question intends.
- (d) Incorrect. Inheritance of acquired characters is the means of transmission, not the cause of loss.
Key point
Lamarck: use and disuse, inheritance of acquired characters; Darwin: variation, struggle, natural selection.
Remember
Loss of limbs in snakes: use and disuse (Lamarck).
Common mistakes
- Choosing natural selection because it is the modern explanation.
- Selecting inheritance of acquired characters.
- Treating burrowing adaptation as the mechanism.
Exam tip
'Loss' of organs in evolution questions usually points to disuse.
Sources
- NCERT Class XII Biology — Evolution
- Encyclopaedia Britannica — Lamarckism