Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Define 'hominin' and describe their key characteristics.
• Identify key hominin fossils found in South Africa.
• Compare the genera Australopithecus and Homo.
• Discuss the 'Out of Africa' hypothesis.

Lesson summary

This week, we delve into the fascinating world of human evolution, focusing specifically on the fossil evidence that supports our understanding of how humans have changed over millions of years. Understanding human evolution isn't just an academic exercise; it provides crucial insights into our origins, our relationships with other species, and the processes that have shaped us into who we are today. South Africa, with its rich fossil record, plays a pivotal role in unraveling this story. From the Sterkfontein Caves (the Cradle of Humankind) to discoveries like Australopithecus sediba, our country is a living laboratory for evolutionary research.

Lesson notes

2. 1. What is a Hominin? A hominin is any member of the taxonomic tribe Hominini, which includes all species more closely related to humans than to chimpanzees. This means that hominins include modern humans (Homo sapiens) and all of our extinct ancestors on the human lineage, such as Australopithecus, Paranthropus, and other Homo species. The key distinguishing characteristics of hominins (which evolved over time) include: Bipedalism: Walking upright on two legs. This is perhaps the most defining characteristic and evolved before large brain size. Evidence for bipedalism can be found in the skeletal structure, particularly the pelvis, femur, and foot.

Reduced Canine Teeth: Hominins have smaller and less projecting canine teeth compared to other apes.

Changes in Skull Morphology: This includes a flatter face, a more parabolic dental arcade (the shape of the row of teeth), and a foramen magnum (the opening at the base of the skull where the spinal cord connects) positioned further forward, indicative of an upright posture.

Larger Brain Size (Encephalization): Over time, hominins evolved larger brains relative to their body size, particularly within the Homo genus.

Tool Use: While some primates use tools, hominins developed increasingly sophisticated tool cultures, indicative of higher cognitive abilities. 2.

2. Key Hominin Fossils in South Africa and Beyond South Africa is a treasure trove of hominin fossils. Here are some notable examples, including their significance: Australopithecus africanus ("Taung Child", "Mrs. Ples"): Discovered in South Africa. Australopithecus africanus is an early hominin that lived between roughly 3.3 and 2.1 million years ago. The Taung Child, discovered in 1924, was the first Australopithecus fossil ever found and provided crucial evidence for the bipedalism of early hominins. "Mrs. Ples", a more complete skull, further supported this.

Significance:* Demonstrated that hominins were bipedal before they evolved large brains. Showed that Africa was a significant site for human origins, which was initially met with skepticism.

Example: Consider the pelvis of Australopithecus africanus. It's broader and shorter than that of a chimpanzee, with a more bowl-shaped structure to support upright walking. The femur also has a valgus angle (angling inward from the hip to the knee), which brings the knees closer to the midline and improves balance during bipedalism.

Australopithecus sediba: Discovered in the Malapa Cave in South Africa. These fossils, dating to approximately 1.98 million years ago, exhibit a mosaic of features, combining characteristics of Australopithecus and Homo.

Significance: Its discovery sparked debate about its position in the human lineage, with some arguing it is a direct ancestor to Homo. The hand bones suggest precision grip, implying tool-making abilities. Homo habilis ("Handy Man"): Fossils of Homo habilis have been found in both East and Southern Africa. Living from about 2.3 to 1.6 million years ago, Homo habilis is characterized by a slightly larger brain size than Australopithecus and is associated with the earliest known stone tools (Oldowan tools).

Significance: Marks a transition towards more human-like traits, including increased brain size and tool use. It is considered one of the earliest members of the Homo genus. Homo erectus ("Upright Man"): Fossils of Homo erectus have been found in Africa, Asia, and Europe, dating from about 1.9 million to 110,000 years ago. Homo erectus had a larger brain size than Homo habilis and a more human-like body proportions. They are associated with more sophisticated tools (Acheulean tools), used fire, and were likely the first hominins to migrate out of Africa.

Significance:* Represents a significant step in human evolution, with increased brain size, advanced tool use, and adaptation to a wider range of environments. Their migration patterns provide insight into hominin dispersal.

Homo naledi: Discovered in the Rising Star Cave system in South Africa. This species, dating to around 335,000 to 236,000 years ago, possesses a unique combination of Australopithecus and Homo traits. The discovery was significant because the remains were found deep within a cave system, suggesting intentional disposal of the dead – a complex behavior previously only attributed to Homo sapiens.

Significance:* Challenged our understanding of the timeline of human evolution and the cognitive abilities of early hominins. Raised questions about the evolution of symbolic behavior. 2.

3. Fossil Evidence and Dating Techniques Fossils provide direct physical evidence of past life. They are the preserved remains or traces of organisms from a former geological age. The study of fossils is called paleontology.

Morphological Characteristics: Comparing the anatomical features (morphology) of different hominin fossils allows us to trace evolutionary changes over time.