Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Describe key trends in hominin evolution (bipedalism, cranial capacity).
• Identify characteristics of Australopithecus africanus and Homo habilis.
• Explain how fossils are dated.
• Discuss the 'Out of Africa' hypothesis.
• Understand that scientific knowledge changes with new evidence.

Lesson summary

Human evolution and the fossil evidence that supports it is a cornerstone of understanding where we, as Homo sapiens, come from. This understanding is crucial for appreciating our place in the world, our relationship with other species, and even informs medical research by providing insights into our genetic vulnerabilities and strengths. In South Africa, with its rich fossil heritage sites like the Cradle of Humankind, this topic takes on even greater significance. Our country is a living laboratory for paleoanthropology, and learning about human evolution connects us directly to our ancient past.

Lesson notes

2. 1.

The Hominin Family Tree: The term "hominin" refers to the group consisting of all modern and extinct Homo species and our immediate ancestors (species more closely related to humans than to chimpanzees). Understanding human evolution involves piecing together the hominin family tree using fossil evidence. This is a complex and constantly evolving process. It is important to recognize that the hominin lineage is not a straight line but a branching bush with many extinct species. 2.

2. Key Trends in Hominin Evolution: Bipedalism (Walking Upright): Arguably the most significant early adaptation. Fossil evidence, such as the Australopithecus "Lucy" skeleton and the Laetoli footprints, demonstrates that bipedalism evolved well before significant increases in brain size. Advantages of bipedalism may have included: Freeing hands for carrying tools and food. Improved predator detection. More efficient locomotion over long distances. Reduced exposure to solar radiation.

Increased Cranial Capacity (Brain Size): Brain size generally increased over time in the hominin lineage. Larger brains are associated with increased cognitive abilities, problem-solving skills, and social complexity.

Changes in Dentition (Teeth): Hominin teeth became smaller and more uniform over time. Canine teeth, in particular, became less prominent and less sexually dimorphic (less difference in size between males and females). This reflects changes in diet from tougher, plant-based foods to softer foods, including meat. The jaw shape also changed from a U-shape to a more parabolic shape.

Facial Structure: The brow ridge (supraorbital ridge) became less pronounced, and the face became flatter.

Tool Use: The development and use of tools became increasingly sophisticated over time, indicative of increasing intelligence and manual dexterity. 2.

3. Key Hominin Fossils and Species: Australopithecus africanus ("Mrs. Ples" and the Taung Child): Age: Approximately 2-3 million years old.

Location: Found in South Africa (Cradle of Humankind).

Characteristics: Bipedal but also capable of climbing trees. Cranial capacity of around 450-550 cm³. Relatively large teeth compared to Homo species. Prognathism (protruding jaw).

Significance: Evidence of early bipedalism in a hominin species. "Mrs. Ples" is a particularly well-preserved cranium. The Taung Child was crucial evidence as well. Homo habilis ("Handy Man"): Age: Approximately 1.4-2.4 million years old.

Location: Found in East Africa (e.g., Olduvai Gorge, Tanzania).

Characteristics: Slightly larger brain size than Australopithecus (around 600-750 cm³). Smaller teeth than Australopithecus. Associated with the earliest known stone tools (Oldowan tools).

Significance: Evidence of early tool use and a possible transition towards the Homo lineage. 2.

4. Dating Methods: Relative Dating: Determines the relative age of a fossil compared to other fossils or rock layers.

Stratigraphy: The principle that in undisturbed rock layers, the oldest layers are at the bottom and the youngest are at the top. Fossils found in lower layers are older than those found in upper layers.

Fluorine Dating: Bones absorb fluorine from the soil over time. Bones in the same soil that have similar fluorine content are likely to be of similar age. This method is limited to comparing bones from the same site.

Absolute Dating (Radiometric Dating): Provides an actual age for a fossil or rock sample.

Carbon-14 Dating: Used to date organic materials up to around 50,000 years old. Carbon-14 is a radioactive isotope of carbon that decays at a known rate (half-life of 5,730 years). By measuring the amount of Carbon-14 remaining in a sample, scientists can estimate its age.

Example: A fossil bone is found to contain 25% of the original Carbon-

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4. How old is the fossil? Half-life = 5730 years 25% remaining means it has gone through two half-lives (100% -> 50% -> 25%) Age of fossil = 2 5730 years = 11460 years Potassium-Argon Dating: Used to date older rocks and fossils (millions of years old). Potassium-40 decays into Argon-40 with a very long half-life (1.3 billion years). This method is used to date volcanic rocks associated with fossil finds. 2.

5. The "Out of Africa" Hypothesis: This hypothesis proposes that Homo sapiens evolved in Africa and then migrated out to populate the rest of the world, replacing earlier hominin populations such as Neanderthals. Evidence supporting this hypothesis includes: The oldest Homo sapiens fossils have been found in Africa. Greater genetic diversity exists among African populations compared to other populations, suggesting a longer period of evolutionary history in Africa. Genetic studies show that non-African populations are descended from a relatively small group of Africans who migrated out of Africa. 2.

6. Interpretations and Debates: The fossil record is incomplete, and new discoveries are constantly being made.

Therefore, interpretations of human evolution are constantly being revised.