Lesson Notes By Weeks and Term v5 - Grade 12
Human evolution and fossil evidence – Week 8 focus
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Human evolution and fossil evidence – Week 8 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Life Sciences
Class: Grade 12
Term: 2nd Term
Week: 8
Theme: General lesson support
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Human evolution is a fascinating journey that traces our origins and how we became who we are today. Understanding this process isn't just about memorizing names of fossils; it's about grasping the scientific principles that govern change over vast periods. In South Africa, we have a unique connection to this story. Our country is often called the "Cradle of Humankind" due to the numerous significant hominin fossil discoveries made here, shaping our understanding of human ancestry. These discoveries directly contribute to the narrative of our shared heritage and provide tangible evidence for evolution.
2. 1. What is a Hominin? A hominin is any member of the zoological family Hominidae, which includes all modern and extinct great apes, that are more closely related to humans than to chimpanzees. Hominins are characterized by bipedalism (walking upright on two legs), reduced canine teeth, and an increasing brain size over time. It's important to distinguish hominins from hominids; the latter refers to the broader family encompassing humans, apes, and their ancestors. 2.
2. Key Trends in Hominin Evolution: Several key trends define the evolutionary pathway of hominins: Bipedalism: The ability to walk upright on two legs. This is perhaps the earliest and most defining characteristic of hominins. Advantages of bipedalism include freeing hands for carrying tools and food, a better view of surroundings, and increased efficiency in hot climates (reduced surface area exposed to direct sunlight). Anatomical adaptations for bipedalism include: Foramen magnum position (position of the hole in the base of the skull where the spinal cord connects): in humans, it's positioned more centrally under the skull, allowing for a balanced head position during upright walking. In quadrupedal apes, it's located further back.
Pelvic girdle: human pelvis is shorter, broader, and bowl-shaped to support the upright posture and provide attachment for powerful leg muscles.
Spine: humans have an S-shaped spine to provide shock absorption and maintain balance.
Femur: the human femur is angled inward (bicondylar angle), bringing the knees closer to the midline for better balance.
Foot: human foot has an arch to provide support and shock absorption.
Cranial Capacity: The size of the braincase, which correlates with brain size. Over time, hominin brain size has generally increased, leading to greater cognitive abilities, tool use, and social complexity.
Jaw and Teeth: Hominin jaw structure and dentition have evolved from a U-shaped jaw with large canines and a diastema (gap between the canine and incisor teeth) in apes, to a parabolic (more rounded) jaw with smaller canines and no diastema in humans. Tooth enamel also thickened over time, possibly as an adaptation to a diet of harder foods.
Brow Ridges: Bony ridges located above the eye sockets. These ridges were more prominent in early hominins and gradually reduced in size in later Homo species.
Facial Prognathism: Refers to the degree to which the face projects forward. Early hominins had more prognathic faces, while later Homo species have flatter, more orthognathic faces. 2.
3. Key Hominin Fossils and Species: It's crucial to remember that the hominin fossil record is incomplete, and our understanding is constantly evolving with new discoveries. Here are some key fossils and species, with a focus on South African discoveries: Australopithecus africanus: Description: An early hominin species that lived in South Africa. Characterized by bipedalism, a relatively small brain size (around 450-550 cc), ape-like facial features, and relatively large teeth.
Key South African Fossils: Taung Child: Discovered in 1924 by Raymond Dart. A juvenile skull that showed evidence of bipedalism and human-like teeth. Mrs.
Ples: Discovered in Sterkfontein Caves in 1947 by Robert Broom. A relatively complete skull that provides valuable information about the facial features and cranial capacity of A. africanus.
Significance: Australopithecus africanus is considered a crucial link in human evolution, demonstrating the emergence of bipedalism before significant brain expansion.
Homo habilis: Description: An early Homo species known for its association with the earliest stone tools (Oldowan tools). Had a slightly larger brain size than Australopithecus (around 600-750 cc) and smaller teeth.
Significance: Homo habilis represents a significant step in hominin evolution, with increased brain size and the development of tool use.
Homo erectus: Description: A more advanced Homo species with a larger brain size (around 850-1100 cc), a more human-like body proportions, and the use of more sophisticated tools (Acheulean tools).
Significance: Homo erectus was the first hominin species to migrate out of Africa and colonize other parts of the world. They were also skilled hunters and possibly used fire.
Homo naledi: Description: Discovered in the Rising Star Cave system in South Africa in
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3. Homo naledi exhibits a mix of Australopithecus and Homo characteristics, including a small brain size (around 465-560 cc), a Homo-like hand and foot, and unique shoulder anatomy.
Significance: The discovery of Homo naledi challenged existing notions about hominin evolution and raised questions about the relationship between brain size and behavioral complexity. The deliberate disposal of bodies in the cave suggests potential ritualistic behavior.
Homo sapiens: Description: Modern humans. Characterized by a large brain size (around 1350 cc), a high forehead, a chin, and relatively gracile skeletal features.