Biology • Year 11 • Module 3 • Lesson 8
Human Evolution
Apply morphological evidence for bipedalism, interpret the hominid timeline, and evaluate the strengths and limitations of fossil evidence and ancient DNA.
1. Interpret bipedalism evidence
The table below shows four skeletal features and what each indicates. Use the data to answer the questions. 8 marks
| Skeletal feature | Observation in bipedal hominins |
|---|---|
| Foramen magnum position | Central, underneath skull |
| Pelvis shape | Broader and more bowl-shaped |
| Femur angle | Inward angle (valgus knee) |
| Foot structure | Arched, adapted for weight-bearing |
1.1 Explain why a centrally positioned foramen magnum indicates upright posture rather than a hunched quadrupedal stance. 2 marks
1.2 A fossil is found with a very posteriorly placed foramen magnum and a narrow pelvis. Predict whether this fossil is likely to be bipedal or quadrupedal. Justify using two features from the table. 3 marks
1.3 Why is it important to use multiple skeletal features rather than one feature alone when arguing that a hominid fossil was bipedal? 3 marks
2. Cause-and-effect chain — why Homo naledi matters
Complete the cause-and-effect chain below. Each cause is given; fill in the effect. 5 marks
Cause 1: Simple models of human evolution assumed that each later hominid must be more “advanced” than earlier ones in all traits.
Effect 1 / Cause 2:
Cause 3: In 2015, Homo naledi was announced with 1,550 fossils showing a mosaic of primitive features (small brain, curved fingers) and more modern features (teeth, feet).
Effect 3 / Cause 4:
Cause 5: Scientists compare fossil evidence with ancient DNA to reconstruct relationships among hominid lineages.
Effect 5 (Overall outcome):
3. Case study — ancient DNA and Neanderthal interbreeding
Read the scenario, then answer the questions. 6 marks
Scenario. Researchers extracted ancient DNA from several Neanderthal fossils and compared it with the genomes of modern humans from Africa and from Europe, East Asia and Oceania. They found that modern non-African populations carry approximately 1–4% Neanderthal DNA, while populations of Indigenous Oceanian descent carry additional Denisovan ancestry. These findings cannot be inferred from the physical appearance of modern or fossil remains alone.
3.1 Explain what this ancient DNA evidence reveals about the relationship between early Homo sapiens and Neanderthals. 2 marks
3.2 Explain one limitation of ancient DNA evidence, using the scenario to support your answer. 2 marks
3.3 Explain why combining fossil evidence and ancient DNA evidence is stronger than using either type alone. 2 marks
Q1.1 — Foramen magnum and upright posture (2 marks)
A centrally positioned foramen magnum (underneath the skull) indicates that the skull balanced over a vertically aligned spine [1]. In quadrupedal animals the foramen magnum is positioned more posteriorly, with the head angled forwards from a horizontal spine. A central position is only mechanically appropriate when the spine is vertical — consistent with bipedal upright walking [1].
Q1.2 — Predicting bipedalism from features (3 marks)
The fossil is likely quadrupedal or at least not fully bipedal [1]. A posteriorly placed foramen magnum indicates the head is held in front of the spine rather than balanced on top, which is the posture of non-bipedal animals [1]. A narrow pelvis also indicates the organism does not need broad support for an upright walking gait and cannot maintain the bowl-shaped support required to carry body weight through the hips in upright locomotion [1].
Q1.3 — Why multiple features matter (3 marks)
Individual features may be incomplete or ambiguous in isolated fossils [1]. Using multiple features provides converging evidence — if several anatomical indicators all point to bipedalism (central foramen magnum, broad pelvis, angled femur, arched foot), the interpretation is much stronger than if only one feature is present [1]. Multiple lines of evidence reduce the risk of misinterpretation from a single unusual or damaged specimen [1].
Q2 — Cause-and-effect chain (sample answers)
Effect 1 / Cause 2: Scientists expected that the timeline would show a smooth progression of improvement, with every successive hominid having a larger brain and fewer primitive features than the one before.
Effect 3 / Cause 4: Homo naledi does not fit a simple ladder. Despite living relatively recently, it retained a small brain and curved fingers alongside more modern features. This directly contradicts the assumption that later always means more “advanced” in all respects.
Effect 5 (Overall outcome): Human evolution is now understood as a branching pattern in which multiple lineages coexisted and evolved differently. No single line of evidence alone is sufficient; fossils show anatomy while ancient DNA tests genetic relatedness and interbreeding, and together they produce a stronger reconstruction.
Q3.1 — What ancient DNA reveals (2 marks)
The ancient DNA evidence reveals that early Homo sapiens and Neanderthals interbred, not just coexisted [1]. The presence of Neanderthal DNA in modern non-African populations is direct genetic evidence that gene flow occurred between these lineages during or after the Out of Africa migration of modern humans [1].
Q3.2 — One limitation of ancient DNA (2 marks)
Ancient DNA survives only in some conditions; it is not available from every fossil [1]. The scenario shows that this research required suitable preserved specimens from which DNA could be extracted — many older or more tropically located fossils cannot yield DNA, meaning ancient DNA evidence cannot be applied to every hominid lineage or time period [1].
Q3.3 — Why combining evidence is stronger (2 marks)
Fossil evidence shows physical anatomy directly (skull shape, pelvis, limb proportions) but cannot detect interbreeding [1]. Ancient DNA tests genetic relationships and can detect interbreeding events, but is unavailable for many fossils. When both lines agree — e.g. fossils show coexistence in time and place, DNA confirms gene flow — the conclusion is stronger than either source could provide alone [1].