Human Evolution
NTSE Biology – Study Notes
(Grade 10 – 12, 2024)
1. Simple Explanation
Human evolution is the gradual change of our ancestors over millions of years that led to the modern Homo sapiens. It is a story of adaptation to changing environments, driven by natural selection, genetic drift, migration, and social behaviour.
Key ideas:
- Bipedalism → walking on two legs.
- Tool use → from simple stone flakes to complex technology.
- Brain expansion → larger, more complex brain relative to body.
- Sociality → cooperation, language, culture.
2. Key Points
| Category | What We Know | Evidence |
|---|---|---|
| Origin of life | Life began ~3.5 billion years ago (prokaryotes). | Fossilized micro‑organisms, stromatolites. |
| Eukaryotes & multicellularity | ~2 billion years ago. | Fossils of single‑cell eukaryotes, filamentous algae. |
| Vertebrates | Fish → amphibians → reptiles → mammals. | Fossil record, transitional forms (e.g., Tiktaalik). |
| Primates | ~65‑60 Ma (million years ago). | Fossils of Ardipithecus, Proconsul. |
| Hominids | ~7 Ma onward. | Fossils: Sahelanthropus, Orrorin, Ardipithecus, Australopithecus, Paranthropus, Homo spp. |
| Bipedalism | Early Australopithecus (~4 Ma). | Footprints (Laetoli), pelvis, femur morphology. |
| Tool use | Homo habilis (~2.4 Ma). | Oldowan stone tools. |
| Brain size | Gradual increase: H. habilis (~600 cc) → H. erectus (~900 cc) → H. sapiens (~1350 cc). | Endocasts, cranial capacity. |
| Language & culture | Complex language by H. sapiens (~200 kya). | Anatomical evidence, symbolic artefacts. |
| Migration | Out‑of‑Africa ~70 kya. | Genetic markers (mtDNA, Y‑chromosome), fossils in Europe, Asia. |
| Genetic evidence | DNA shows common ancestry with chimpanzees (≈6 Ma). | Comparative genomics, SNP analysis. |
| Modern humans | H. sapiens (modern) appeared ~200 kya. | Fossils (Jebel Irhoud, Omo Kibish), DNA. |
Important Fossils & Dates
| Species | Approx. Age | Key Feature |
|---|---|---|
| Sahelanthropus tchadensis | 7 Ma | Possible bipedal pelvis |
| Ardipithecus ramidus | 4.4 Ma | Bipedal gait, arboreal adaptations |
| Australopithecus afarensis (Lucy) | 3.2 Ma | 1‑1.4 m tall, bipedal |
| Paranthropus boisei | 2.3 Ma | Robust jaws, large molars |
| Homo habilis | 2.4 Ma | First stone tools |
| Homo erectus | 1.8 Ma | Brain ~900 cc, fire control |
| Homo neanderthalensis | 400 kya | Adapted to cold, complex tools |
| Homo sapiens | 200 kya | Modern anatomy, artistry |
3. Worked Example
Constructing a Simple Phylogenetic Tree for Early Hominins
- Choose taxa: Sahelanthropus, Ardipithecus, Australopithecus, Homo habilis, Homo erectus.
- Identify shared derived traits (synapomorphies):
- Sahelanthropus & Ardipithecus: bipedal pelvis.
- Ardipithecus & Australopithecus: long legs, short arms.
- Australopithecus & Homo habilis: larger braincase.
- Homo habilis & Homo erectus: stone tools, larger brain.
- Cluster taxa by similarity
- Group 1: Sahelanthropus & Ardipithecus (early bipedal).
- Group 2: Australopithecus (bipedal, larger brain).
- Group 3: Homo spp. (tools, brain expansion).
- Draw tree
┌─Sahelanthropus ┌───┤ │ └─Ardipithecus
─────┤ │ ┌─Australopithecus └───┤ └─Homo (habilis → erectus)
5. **Interpretation**
- The tree shows a linear progression from early bipedal hominins to tool‑using *Homo*.
- It illustrates how new traits appear at branching points.
**Takeaway**: Phylogenetics