Biology • Year 11 • Module 3 • Lesson 11
Anatomical Evidence
Lock in the core vocabulary, the distinction between homologous and analogous structures, vestigial structures, the pentadactyl limb, and the significance of comparative embryology as evidence for evolution.
1. Term–definition match
The eight definitions below are shuffled. In the right-hand column write the matching term from this list: homologous structure, analogous structure, vestigial structure, pentadactyl limb, convergent evolution, divergent evolution, comparative embryology, pharyngeal arch. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | Similar body parts in related species that share the same underlying anatomy and evolutionary origin, even if their current functions differ. | |
| 1.2 | The independent evolution of similar-looking structures in unrelated lineages due to similar selective pressures. | |
| 1.3 | A reduced, non-functional body part inherited from an ancestor in which it served a purpose. | |
| 1.4 | The five-digit limb plan shared by all vertebrates, considered the classic example of a homologous structure. | |
| 1.5 | Similar structures in unrelated species that perform the same function but have different evolutionary origins. | |
| 1.6 | The accumulation of differences between related species descending from a common ancestor, often driven by different selection pressures. | |
| 1.7 | The study of shared structural features in the early embryos of different species as evidence for common ancestry. | |
| 1.8 | A transient structure found in the embryos of all vertebrate groups, evidence of shared developmental pathways from a common ancestor. |
2. Classify examples
For each example below, identify whether the structures are homologous, analogous or vestigial. Then write one justifying sentence. 8 marks (1 per classification, 1 per justification)
2.1 Whale flipper and human arm — both contain humerus, radius, ulna, carpals and phalanges.
Classification: _________________ Justification:
2.2 Bird wing and insect wing — both used for flight but have entirely different internal structure.
Classification: _________________ Justification:
2.3 Human coccyx — a small set of fused bones at the base of the spine with no current locomotor function.
Classification: _________________ Justification:
2.4 Shark body and dolphin body — both streamlined with dorsal fins, but one is a cartilaginous fish and the other a mammal.
Classification: _________________ Justification:
3. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 6 marks (1 for T/F, 1 for correction where needed)
3.1 Analogous structures are the best evidence for common ancestry because similar structures must share an evolutionary origin. T / F
3.2 The pentadactyl limb is found in the forelimbs of humans, bats, whales and horses, making it the classic example of a homologous structure among vertebrates. T / F
3.3 Vestigial structures are evidence against evolution because they show that organisms have useless parts that serve no purpose. T / F
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 Why are homologous structures considered strong evidence for common ancestry, even when they perform different functions?
4.2 Why can convergent evolution cause analogous structures to mislead classification based on appearance?
4.3 What do whale pelvic bones suggest about the evolutionary history of whales?
4.4 Why is the similarity of early vertebrate embryos (e.g. sharing pharyngeal arches and tails) significant as evolutionary evidence?
Q1 — Term–definition matches
1.1 homologous structure • 1.2 convergent evolution • 1.3 vestigial structure • 1.4 pentadactyl limb • 1.5 analogous structure • 1.6 divergent evolution • 1.7 comparative embryology • 1.8 pharyngeal arch.
Q2 — Classify examples
2.1 Homologous. The whale flipper and human arm share the same underlying bone plan (humerus, radius, ulna, carpals and phalanges) inherited from a common vertebrate ancestor, even though one is used for swimming and the other for manipulating objects.
2.2 Analogous. Bird wings and insect wings both enable flight but have entirely different internal structures and evolutionary origins — one arose in vertebrates, the other in arthropods, through convergent evolution driven by the same selective pressure.
2.3 Vestigial. The human coccyx is a reduced remnant of a tailed ancestry found in earlier primates and other vertebrates; it no longer serves its ancestral locomotor function in humans, showing that evolution modified rather than erased the ancestral body plan.
2.4 Analogous. A streamlined body with dorsal fins arose independently in sharks (cartilaginous fish) and dolphins (mammals) because both lineages evolved under similar selective pressure for fast aquatic movement — they do not share a close recent ancestor.
Q3 — True / False with correction
3.1 False. Correction: Homologous structures (same underlying anatomy and origin) are the best evidence for common ancestry. Analogous structures arise through convergent evolution and reflect similar selective pressures, not close ancestry. Similar appearance alone does not indicate shared origin.
3.2 True.
3.3 False. Correction: Vestigial structures are strong evidence for evolution. They show that evolution modifies existing body plans rather than designing organisms from scratch — a vestigial structure is a retained remnant of an ancestral feature, exactly what descent with modification predicts.
Q4.1 — Why homologous structures show common ancestry
Homologous structures share the same underlying anatomical origin even if they perform different functions today. This shared underlying plan is best explained by descent from a common ancestor that possessed the same basic structure — different lineages then modified it for different uses through divergent evolution.
Q4.2 — Why convergent evolution misleads classification
Convergent evolution produces superficially similar-looking structures in unrelated lineages responding to the same environmental pressures. If classification is based only on physical appearance, these organisms could be grouped together as close relatives when in fact their similarity reflects independent adaptation, not shared ancestry. Molecular or structural analysis is needed to resolve the true relationship.
Q4.3 — What whale pelvic bones suggest
Whale pelvic bones are vestigial remnants of functional hind limb bones possessed by the land-dwelling ancestors of whales. Their presence suggests that modern whales descended from terrestrial ancestors and that evolution retained reduced versions of these structures rather than removing them completely — consistent with descent with modification.
Q4.4 — Significance of early embryo similarity
Early vertebrate embryos of fish, reptiles, birds and mammals share structural features such as pharyngeal arches and tails. These shared embryological patterns suggest common ancestry and conserved developmental pathways — the same developmental programs have been inherited and modified across very different vertebrate groups, which is what would be expected if they all descended from a common ancestor.