The forelimbs of frog, lizard, bird, and human are examples of which type of organs in evolutionary biology?

Introduction / Context:
Comparative anatomy provides evidence for evolution by showing how structures in different organisms are related. Two key concepts are homologous and analogous organs. Homologous organs share a common evolutionary origin but may have different functions, while analogous organs have similar functions but evolved independently. This question focuses on the classification of forelimbs in different vertebrates, a classic example used in textbooks.

Given Data / Assumptions:

• The organisms listed are frog, lizard, bird, and human.
• The structures considered are their limbs.
• Options refer to homologous versus analogous relationships.
• We assume understanding of basic evolutionary terminology.

Concept / Approach:
Homologous organs arise from the same embryonic structures and share a common evolutionary origin, even if they differ in appearance or function in adults. The forelimbs of vertebrates such as frogs, lizards, birds, and humans all derive from the same basic limb pattern. Each forelimb contains similar sets of bones, including humerus, radius, ulna, carpals, metacarpals, and phalanges, although they are modified for different functions such as jumping, walking, flying, or manipulating objects. Analogous organs instead show similar function without shared origin, such as wings of birds and wings of insects. Therefore, the limbs in the question are homologous organs.

Step-by-Step Solution:
Step 1: Identify the structures being compared: forelimbs of frog, lizard, bird, and human. Step 2: Recall that these animals are all vertebrates with a similar basic skeleton in the forelimb. Step 3: Note that although functions differ–jumping in frog, support and walking in lizard, flight in bird, manipulation in human–the underlying bone pattern shows common origin. Step 4: Recognise that shared origin with modified structure and function defines homologous organs. Step 5: Choose homologous organs with common origin but modified structure and function as the correct description.

Verification / Alternative check:
Anatomical diagrams of vertebrate forelimbs consistently show the same sequence of long bones and digits, labelled with the same names, in frog, lizard, bird, and human. Evolutionary biology texts use these diagrams as evidence for divergent evolution, where a common ancestral limb plan is modified for different modes of life. In contrast, examples of analogous organs include wings of birds and bats compared to wings of insects, which use different structural materials and developmental pathways. This supports the classification of the listed limbs as homologous.

Why Other Options Are Wrong:

• Homogenous organs with identical external form and function only: The external form and function of these limbs are quite different, and homogeneity is not the key evolutionary concept.
• Heterogeneous organs with no evolutionary relationship: This ignores the shared vertebrate limb pattern and evolutionary lineage.
• Analogous organs with similar function but different origin: The functions differ widely, and the organs share a common origin, so they are not analogous.

Common Pitfalls:
Students sometimes confuse homologous and analogous because both involve comparisons of organs. A useful rule is that homologous means same origin, while analogous means same function. In this example, the origin is the same but functions are different, so the organs are homologous. Remembering the classic diagrams of vertebrate forelimbs can help you answer such questions quickly.

Final Answer:
The limbs of frog, lizard, bird, and human are homologous organs with a common origin but modified structure and function.