Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Describe key hominin characteristics (bipedalism, brain size, teeth).
• Identify and compare key South African hominin fossils.
• Explain the 'Out of Africa' hypothesis.
• Analyze evidence for mosaic evolution.
• Understand how fossils show evolutionary relationships.

Lesson summary

Human evolution is the process by which modern humans evolved from earlier hominins. Understanding human evolution helps us understand our place in the natural world, our relationship to other living things, and the history of life on Earth. The fossil record, particularly the rich fossil finds in South Africa (the Cradle of Humankind), provides crucial evidence for this evolutionary journey. Studying these fossils allows us to trace the lineage of humans, understand the adaptations that allowed us to thrive, and appreciate the impact of our species on the planet.

Lesson notes

2. 1. What are Hominins? Hominins are members of the tribe Hominini, which includes modern humans and all of our extinct ancestors more closely related to humans than to chimpanzees. This means understanding what separates humans from our closest living relatives is key. The key features that distinguish hominins include: Bipedalism (Walking upright on two legs): This is perhaps the most defining characteristic. Bipedalism frees the hands for carrying objects, using tools, and scanning the environment for predators. Skeletal adaptations for bipedalism include: Foramen magnum position:* In humans, the foramen magnum (the hole in the skull where the spinal cord enters) is located at the base of the skull, directly beneath the brain. In apes, it's located further back.

Pelvis shape:* Human pelvises are shorter and broader than ape pelvises, providing more support for upright posture.

Spine curvature:* Humans have an S-shaped spine, which helps to distribute weight evenly and maintain balance.

Leg and foot structure:* Longer legs relative to arms, an angled femur (thigh bone), and an arched foot (for shock absorption) are adaptations for efficient bipedal walking.

Increased Cranial Capacity (Brain Size): Hominin brain size has increased significantly over time. Larger brains are associated with increased cognitive abilities, such as language, tool use, and social complexity.

Dentition (Teeth): Hominin teeth tend to be smaller than those of apes, with thicker enamel. The canine teeth are reduced in size and do not project beyond the other teeth. The shape of the dental arcade (the arrangement of the teeth in the jaw) is also different; humans have a parabolic (U-shaped) arcade, while apes have a more rectangular one.

Tool Use: Although some apes use tools, hominins developed more sophisticated and varied tool technologies. 2.

2. South African Hominin Fossils: South Africa's "Cradle of Humankind" is a UNESCO World Heritage Site renowned for its rich hominin fossil discoveries.

Let's look at some key examples: Australopithecus africanus: Discovered by Raymond Dart in Taung in 1924, the "Taung Child" is a famous A. africanus fossil. This species lived approximately 3.0–2.0 million years ago.

Key features include: Bipedalism, evident from the foramen magnum position. Relatively small brain size (around 450 cc). Ape-like face with a projecting jaw. Evidence of arboreal (tree-dwelling) adaptations, suggesting they were not exclusively bipedal.

Example: Imagine you are a paleoanthropologist analyzing the Taung Child skull. The forward position of the foramen magnum is a clear indication that A. africanus walked upright. This single feature is a piece of the puzzle confirming bipedalism as an early hominin trait.

Paranthropus robustus: Discovered in Kromdraai, near Sterkfontein, this species lived approximately 2.0–1.2 million years ago.

Paranthropus species are characterized by: Massive jaws and cheek teeth, adapted for chewing tough plant matter. A sagittal crest (a ridge of bone on the top of the skull) to which powerful chewing muscles were attached. Relatively small brain size (around 500 cc).

Example: The P. robustus fossil known as "DNH 7" shows the extremely robust jaw and teeth typical of this species. These features indicate a diet heavily reliant on tough, fibrous plant material, likely as an adaptation to the changing environment of the time.

Homo naledi: Discovered in the Rising Star Cave system in 2013, H. naledi is a more recent and controversial discovery. It lived approximately 335,000–236,000 years ago.

Key features include: A small brain size (around 560 cc), similar to Australopithecus. A human-like hand and foot structure, suggesting bipedalism and the ability to use tools. A relatively slender body build. Controversy surrounds the deliberate disposal of the dead within the cave system.

Example: The discovery of numerous H. naledi skeletons in the Rising Star Cave raises questions about their cognitive abilities and social behavior. The deliberate placement of bodies suggests a level of ritualistic behaviour not previously associated with hominins with such a small brain size. 2.

3. The 'Out of Africa' Hypothesis: The 'Out of Africa' hypothesis proposes that Homo sapiens evolved in Africa and then migrated to other parts of the world, replacing earlier hominin populations such as Neanderthals and Homo erectus. The evidence supporting this hypothesis includes: Fossil evidence: The oldest Homo sapiens fossils have been found in Africa.

Genetic evidence: Genetic studies show that African populations have the greatest genetic diversity, suggesting that they are the oldest human populations. These studies trace the lineage of all modern humans back to Africa. 2.

4. Mosaic Evolution: Mosaic evolution refers to the concept that different traits evolve at different rates and at different times. For example, bipedalism evolved before large brain size in hominins.