Q.29 Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: The wing of a bird, forelimb of human and forelimb of lizard are homologous.

Reason R: Organ’s underlying similarity arises due to their derivation from common ancestors.

In the light of the above statements, choose the most appropriate answer from the options given below:

1. Both A and R are correct and R is the correct explanation of A

2. Both A and R are correct but R is NOT the correct explanation of A

3. A is correct but R is not correct

4. A is not correct but R is correct

Homologous Forelimbs in Bird, Human, Lizard: Assertion-Reason Explained

Bird wings, human arms, and lizard forelimbs share the same basic bone structure from a common tetrapod ancestor. Reason R correctly explains this homology through shared evolutionary descent.​

Correct Answer

1. Both A and R are correct and R is the correct explanation of A. Assertion A states these forelimbs are homologous, sharing humerus, radius, ulna despite different functions. Reason R accurately explains homology arises from common ancestry.

Option Breakdown

Option 1: Both Correct, R Explains A

Correct. All three forelimbs trace to a ~350 million-year-old tetrapod ancestor with identical bone layout, modified for flight (bird), manipulation (human), or crawling (lizard). R directly justifies A’s homology claim.

Option 2: Both Correct, R Doesn’t Explain A

Incorrect. R precisely defines homology’s cause—derivation from common ancestors—making it the logical explanation, not unrelated.​

Option 3: A Correct, R Incorrect

Wrong. A holds true per anatomical evidence (same bones, embryonic origins). R states standard evolutionary biology definition of homology.​

Option 4: A Incorrect, R Correct

False. A is factual; these aren’t analogous (similar function unrelated ancestry) but homologous (different function, shared origin). R remains valid.