Lesson Notes By Weeks and Term v5 - Grade 12

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Performance objectives

• Define 'hominin' and describe their key characteristics.
• Identify at least three significant hominin fossils from South Africa.
• Explain the 'Out of Africa' hypothesis and its evidence.
• Discuss the trends observed in hominin evolution.
• Compare characteristics of different Homo species.

Lesson summary

This week, we delve into the fascinating world of human evolution, focusing on the fossil evidence that supports our understanding of how modern humans ( Homo sapiens) came to be. This is incredibly relevant to us in South Africa because our country is renowned as one of the richest sources of hominin fossils globally, often called the "Cradle of Humankind." Understanding human evolution helps us appreciate our shared ancestry and understand the biological processes that have shaped us. It also highlights the importance of preserving fossil sites for future generations. South Africa's fossil discoveries, like Australopithecus africanus ("Mrs.

Lesson notes

2.1 Hominins and Hominids: A hominid refers to all modern and extinct great apes (modern humans, chimpanzees, gorillas, orangutans, and all their immediate ancestors). A hominin refers to modern humans and all our extinct bipedal ancestors. The key difference lies in the inclusion of non-bipedal great apes in the hominid group. It's crucial to use the correct term when referring to human evolutionary ancestors. Key characteristics that differentiate hominins from other primates: Bipedalism: The ability to walk upright on two legs. This is perhaps the defining characteristic of hominins.

Adaptations for bipedalism include: Foramen magnum position:* Located centrally at the base of the skull, allowing the head to balance on the vertebral column. In other primates, it's located further back.

S-shaped spine:* Provides better balance and shock absorption.

Pelvis shape:* Shorter and broader pelvis for better weight distribution and muscle attachment for bipedal locomotion.

Femur angle:* The femur angles inwards from the hip to the knee (bicondylar angle or carrying angle), positioning the knees closer to the body's midline for stability.

Foot structure:* Arched foot for shock absorption and a non-opposable big toe aligned with other toes for efficient walking.

Cranial Capacity: Hominins generally have a larger brain size compared to other primates. Brain size increased significantly throughout hominin evolution.

Dentition: Changes in teeth and jaw structure. Hominins have smaller canines and thicker enamel on their molars compared to other primates, reflecting a dietary shift. The presence of a diastema (gap between the incisors and canines) is typically reduced or absent.

Tool Use: Although some primates use tools, hominins developed increasingly sophisticated tools, indicating advanced cognitive abilities.

Facial Features: A flatter face with a reduced brow ridge compared to earlier primates. 2.2 Significant Hominin Fossils Discovered in South Africa: South Africa is a treasure trove of hominin fossils.

Here are some prominent examples: Australopithecus africanus ("Mrs. Ples"): Discovered in Sterkfontein Caves. Estimated to be around 2.0-3.0 million years old.

Key features: Relatively small brain size (around 485 cm³), bipedal, smaller canines compared to apes.

Significance:* Showed that bipedalism evolved before significant brain enlargement.

Australopithecus sediba: Discovered in Malapa Cave, near Sterkfontein. Approximately 1.98 million years old.

Key features: Mosaic of Australopithecus and Homo traits, including a relatively small brain size but with Homo-like features in the hands and pelvis.

Significance: Provides insights into the transition from Australopithecus to Homo. Australopithecus prometheus ("Little Foot"): Nearly complete skeleton discovered in Sterkfontein Caves. Estimated to be over 3.67 million years old, making it one of the oldest Australopithecus fossils.

Key features: Primarily bipedal, longer arms than legs, adaptations for both tree climbing and walking.

Significance: Offers a more complete picture of early Australopithecus anatomy.

Homo naledi: Discovered in the Rising Star Cave system near Sterkfontein. Estimated to be between 236,000 and 335,000 years old.

Key features: Small brain size (around 560 cm³), Homo-like features in the skull, teeth, and legs, but also Australopithecus-like features in the shoulders and fingers.

Significance:* Challenges the linear view of human evolution and suggests that multiple hominin species coexisted in Africa. 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 other hominin populations like Neanderthals and Homo erectus.

Supporting Evidence: Fossil Evidence: The oldest Homo sapiens fossils have been found in Africa.

Genetic Evidence: Genetic studies show that the greatest genetic diversity exists among African populations, suggesting that Africa is the origin of Homo sapiens. Genetic data also shows that all non-African populations originated from a single small population that migrated out of Africa. Analysis of mitochondrial DNA and Y-chromosome DNA supports this.

Archaeological Evidence: The oldest and most sophisticated tools associated with Homo sapiens have been found in Africa. Example of using genetic data to support the "Out of Africa" hypothesis: Imagine you analyze mitochondrial DNA (mtDNA) from different human populations. mtDNA is passed down from mother to child and has a relatively high mutation rate. By comparing the differences in mtDNA sequences between populations, you can estimate how long ago they shared a common ancestor. If African populations have the most variations in their mtDNA, it suggests that they have been accumulating mutations for the longest time, indicating that they are the oldest population.