Question
Which of the following is the best evidence that whales and humans share a common ancestor?
(A) Both are warm-blooded (B) The whale flipper and human hand have the same bone arrangement (C) Both give birth to live young (D) Whale embryos pass through a fish-like stage
(NEET 2024 pattern — this type appears almost every year)
Solution — Step by Step
The question is testing your understanding of homologous structures — not just that they exist, but why they count as evidence of common ancestry. Eliminate options by category first.
Options A and C (warm-blooded, live birth) are convergent traits — features that evolved independently in different lineages because they solve the same survival problem. These tell us about natural selection pressure, not shared ancestry. Rule them out.
Option D refers to the recapitulation concept (Haeckel’s observation). Whale embryos do show gill slits and a fish-like tail at early stages. This is evidence of evolution, but it’s embryological evidence — not the strongest link specifically between whales and humans.
The whale flipper and human hand share the same bones: humerus → radius/ulna → carpals → phalanges. Same blueprint, completely different function. This is the definition of a homologous structure. Same structure = same origin = common ancestor.
Answer: (B) — The whale flipper and human hand have the same bone arrangement.
Why This Works
Homologous structures are the backbone of comparative anatomy as evidence for evolution. The logic is simple: if two organisms independently evolved the same internal bone arrangement for completely different purposes (swimming vs. grasping), that’s statistically impossible. The only explanation is that both inherited the blueprint from a shared ancestor.
The whale lineage returned to the sea around 50 million years ago. Over millions of generations, natural selection reshaped the hand into a flipper — but couldn’t scrap the underlying skeletal plan. Think of it like a contractor renovating a house: the walls change, but the original foundation stays.
This is why homology is considered stronger evidence than analogous structures (like the wings of bats and insects, which look similar but have completely different internal architecture — that’s convergent evolution, not common ancestry).
Alternative Method — The Three Types of Evidence, Mapped
For NEET, you need to quickly classify any example given into its correct evidence category. Here’s the fast map:
| Evidence Type | What to Look For | Example |
|---|---|---|
| Fossils | Preserved remains, geological layers | Archaeopteryx — reptile + bird features |
| Homology | Same structure, different function | Whale flipper, bat wing, human hand, horse forelimb |
| Embryology | Similar embryos across species | All vertebrate embryos have gill pouches |
| Biochemistry | Shared DNA, proteins | Cytochrome c similarity across species |
When the question describes “same internal bones, different external purpose” — that’s homology, every time.
A shortcut for MCQs: homologous = same structure, different function (common ancestry). Analogous = different structure, same function (convergent evolution). The whale flipper vs. fish fin is analogous — don’t mix this up.
Common Mistake
Students confuse homologous and analogous structures — and NEET loves to exploit this. The whale flipper and the fish fin look similar and do the same job (swimming), so students mark them as homologous. They’re not — internally they have completely different bone structures. Homologous structures share internal anatomy; analogous structures share external function. Always ask: “Same bones inside, or just same shape outside?”
A second slip: students sometimes mark embryological evidence (Option D here) as the best answer when asked about whale-human connection specifically. Embryology is valid evidence for evolution broadly, but for a specific whale-human link, homology is more direct and testable — and that’s what NEET wants you to pick.