Human Evolution – Study Notes
Human Evolution – Study Notes
Classification of Humans
Humans are in the class Mammalia.
They belong to the order Primates.
Sub-order: Anthropoidea.
Sub-order is made up of 2 families: Hylobatidae and Hominidae.
Humans fall into the family Hominidae.
Genus: Homo.
Species: Homo sapiens.
Terms to distinguish:
Hominid: the group that includes modern humans, chimpanzees, gorillas and orangutans plus all their immediate ancestors.
Hominin: the group that includes modern humans, extinct human species, and all our immediate ancestors (including Homo, Australopithecus, Paranthropus, Ardipithecus).
Phylogenetic Tree – Family Hominidae
A phylogenetic tree shows relationships among diverse genera that are part of Hominidae (great apes and humans).
Notable genera/species included (from the slide):
Kenyanthropus platyops
Homo rudolfensis, Homo heidelbergensis, Homo sapiens
Ardipithecus ramidus
Australopithecus afarensis, Australopithecus africanus
Paranthropus boisei, Paranthropus robustus
Homo habilis, Homo erectus, Homo floresiensis, Homo neanderthalensis
Time scale shown as Million Years Ago (m.y.a): e.g. 0 to several million years ago.
Lines of Evidence for Common Ancestors (Living Hominids/Humans Included)
Fossil evidence
Genetic evidence
Cultural/Archaeological evidence
Key Shared Features Between Humans and African Apes
Shared primitive traits with apes include features such as:
Protruding jaws
Heavy brow ridges
Sloping faces
Relatively small brain size
Anatomical Differences: African Apes vs Humans
Vertebral column: humans have an S-shaped spine for flexibility and shock absorption; apes have a C-shaped spine.
Pelvic girdle: bipeds require a wider, shorter pelvis to support body weight; quadrupeds have a longer, narrower pelvis.
Limbs: humans have short arms and long legs with well-developed knee joints; apes have long arms and shorter legs; humans have a non-opposable big toe with a developed foot arch; apes have an opposable big toe and flatter feet.
Brain size: humans have a larger, more rounded cranium; apes have smaller brains.
Dentition and prognathism: humans have smaller canines, reduced diastema, flatter molars; apes have large canines and a diastema.
Cranial and brow ridges: apes have prominent brow ridges; humans have reduced ridges.
Bipedalism: Definition, Significance, and Foramen Magnum
Definition: locomotion on two hind legs in an upright position.
Advantages of bipedalism:
Smaller surface area exposed to the sun => reduced overheating.
Larger surface area exposed to air currents => cooling and reduced water needs.
Hands are freed for tool use, carrying objects, offspring, etc.
Ability to see further over varied habitats.
Aids in adapting to a variety of environments.
Foramen magnum position changed from the back of the skull (quadrupedal) to the bottom/forward position (bipedal).
This inward relocation supports upright posture and walking on two legs.
Detailed Anatomy: Vertebral Column, Pelvic Girdle, Limbs, Brain, and Dentition
Vertebral column: S-shaped in humans for flexibility and shock absorption; C-shaped in apes.
Pelvic girdle: humans have a wider, shorter pelvis to support body weight; apes have a longer, narrower pelvis.
Limbs:
Humans: short arms, long legs; knee joints well developed; feet with non-opposable big toe and a high arch.
Apes: long arms, short legs; opposable big toe; flat feet.
Brain size: gradual increase in cranium size over hominin evolution; larger brain facilitates advanced functions.
Canine size and dentition: apes have large canines and diastema; humans have smaller canines, no diastema, and flatter molars.
Prognathism and palate: apes have prognathous jaws with a sloping face; humans have a flatter face and a non-prognathous jaw.
Brow ridges: pronounced in apes, reduced in humans.
Brain and Diet: Dentition and Diet Changes
Brain size overview:
Early hominids show smaller brains (e.g., Ardipithecus ~300–350 cm³).
Later Homo species show larger brains (e.g., Homo sapiens ~1200–1800 ml; Homo erectus ~600–1400 cm³).
Dentition changes:
Diastema (gaps between incisors and canines) present in some early primates; disappears in modern humans.
Canines become smaller; molars and premolars become flatter.
Prognathism: apes have prognathous jaws; humans are non-prognathous with a more vertical face.
Jaw and palate shapes: humans have a C-shaped jaw with a curved palate; apes have U-shaped jaws.
Chin development: humans have a protruding chin; apes lack a pronounced chin.
Zygomatic arch (cheekbone): more pronounced in apes; relatively reduced in humans due to smaller jaw muscles.
Foramen magnum position is related to upright posture (see above).
The significance of these changes ties to diet, tool use, and social communication capabilities.
Fossil Evidence and Key Hominid Genera
Ardipithecus (early hominid, ~5.8–4.4 mya):
Ape-like and australopithecine traits.
Probably bipedal; foramen magnum centrally located; pelvis wide-top and narrow-bottom; long arms for climbing; opposable big toe.
Brain capacity ~300–350 cm³; ape-like dentition; small canines; diastema present; protruding jaw; sloped face.
Palate rectangular; small brow ridges.
Australopithecus (first bipeds, ~4.5–1.5 mya):
Ape-like and human-like traits; bipedal; foramen magnum centrally located; pelvis short and wide; long arms; curved fingers; grasping hallux may be present.
Brain capacity ~380–500 cm³; diastema reduced; teeth more human-like; smaller canines; protruding jaw with no chin; sloping face; U-shaped palate; large brow ridges.
Examples: Taung child; Lucy (Australopithecus afarensis); Mrs. Ples (A. africanus); Australopithecus sediba.
Homo (appeared ~2.2 mya in Africa):
Bipedal; foramen magnum directly above the vertebral column; pelvis short and wide; arms shorter than legs; short, straight toes with non-opposable big toe; opposable thumb; large brain capacity ~600–1400 cm³.
Homo sequence proposed by scientists:
Homo habilis – the “handy man” (toolmakers; Tanzania).
Homo erectus – the “upright man” (near Lake Turkana, Kenya).
Disputed status as ancestor to modern humans; Homo neanderthalensis (Neanderthals) and Homo sapiens follow.
The San (world’s oldest extant people):
Show the greatest genetic diversity in mtDNA; direct descendants of the Homo sapiens group that branched off before global migrations.
Interdependence of Hominid Skills
Bipedalism, fire-making, tool-making, language, and culture are interdependent; development of one supports the others.
Out of Africa Hypotheses vs Multiregional Hypothesis
Homo sapiens originated in Africa about 200,000 years ago and migrated elsewhere, often out-competing other Homo species.
Multiregional hypothesis suggests the Homo genus left Africa and spread worldwide, giving rise to Homo sapiens in various regions; supported by fossil records and genetics.
Evidence cited:
Genetic links: Chromosomal DNA, Mitochondrial DNA, Y-chromosome DNA.
Fossils and artefacts found in Africa (Great Rift Valley in East Africa, Cradle of Humankind in South Africa).
Timeline highlights:
Origin of modern humans: approx. at least by around -160,000 years ago.
Neanderthals in Europe and the latest Homo erectus fossils span from ~1.9 million to ~30,000 years ago.
Homo floresiensis in Southeast Asia (~18,000 years ago).
Transitional Fossils
Definition: fossils that are intermediate between a group and their ancestor; show stages in evolutionary transitions.
Primitive versus Derived Traits in Primates and Humans
Upper limbs and physical traits:
Primates have long arms, free shoulder girdle, flat nails (not claws), and opposable thumbs.
These features allow grasping and precision tasks, enabling tool use.
Brain and vision:
Primates have relatively large brains for body size; frontal brain regions for hand-eye coordination are enlarged.
Olfactory senses are reduced in primates.
Vision: stereoscopic and binocular vision with color vision (cones).
Posture and reproduction:
Primates generally have upright posture, reduced litter sizes, and intensive parental care.
Arboreal vs terrestrial:
Arboreal adaptations persist in some early primates; humans show a major shift to terrestrial bipeds.
Practice and Study Prompts (Extracted from Slides)
3.2.1: Identify Organisms A and B from skull diagrams (gorilla vs modern human).
3.2.2: Tabulate four observable differences between gorilla and human skulls.
3.2.3: Which organism is bipedal for most of its adult life?
3.2.4: Explain two possible advantages of bipedalism.
3.2.5: Name two similarities between organisms A and B.
3.1.1: From diagrams A, B, C, name the species that appeared first, second, and last.
3.1.2: Tabulate three visible structural differences between diagram A and B that illustrate evolutionary trends in human development.
3.1.x (exemplary questions in slides): Distinguish and identify hominid/human skull features across diagrams A, B, C.
Diagram-Based Comparisons (3.1 and 3.2 Studies)
3.2Differences (Gorilla vs Human):
Canines: Gorilla canines well developed; Human canines not well developed.
Face: Gorilla sloping face; Human flat face.
Brow ridges: Gorilla brow ridges well developed; Human brow ridges less developed.
Cranium size: Gorilla smaller cranium/brain; Human larger cranium/brain.
3.2Differences (Cheekbone and Foramen magnum):
Cheek bones: Gorilla wider; Human narrower.
Foramen magnum: Gorilla at back of skull; Human center/more forward.
Chin: Gorilla lacks chin; Human chin well developed.
3.2.3: B is the bipedal organism (most likely Homo sapiens).
3.2.4: Advantages of bipedalism include environment awareness, free hands for tools/offspring, thermoregulation, and social signaling.
3.2.5: Similarities between A and B include: opposable thumbs, binocular vision, grasping hand capabilities, etc.
Diagrams and Identification Exercises (3.1 and 3.2 series)
Diagram A, B, C tasks involve identifying skulls of Homo erectus, Pan troglodytes, Homo sapiens and mapping evolutionary trends.
Example outcomes (from slides):
3.1.1: First, Second, Last correspondences depending on diagram features (see slide prompts).
3.1.2: Three visible structural differences between diagrams illustrate evolutionary trends (e.g., brain size, jaw shape, brow ridges).
Important reminder: Scientific names must be underlined when required by exam conventions.
The 4.3 Essay Prompt (Nov 2013 Paper 1, 4.3)
Task: Describe the structural changes to the skull that characterize the evolution of modern humans from ape-like ancestors, and explain the significance of these changes.
Foramen magnum:
In ape-like beings, the foramen magnum is backward.
In modern humans, it is forward/central/ventral.
Significance: shift from quadrupedalism to bipedalism, enabling row of downstream benefits: increased environmental awareness, free hands for tools/offspring, improved thermoregulation, etc.
Cranium (braincase):
Modern humans have larger, more rounded cranium; less sloping forehead.
Significance: space for larger brain enabling better coordination, information processing, language, and tool use.
Jaws and dentition:
Humans have smaller jaws, non-prognathous (flat face) with a C-shaped jaw; apes have prognathous jaws with a U-shaped palate and larger canines.
Significance: dietary shift toward softer cooked foods; reduced need for large biting muscles; changes in facial projection and social signaling.
Dentition details and chin:
Diastema disappears; canines smaller; flatter molars and premolars.
Chin development in humans provides structural support for speech.
Brow ridges and zygomatic arches:
Reduced brow ridges; zygomatic arches smaller due to decreased muscle attachment from smaller jaws.
Significance of changes overall:
Enabled higher brain function, language development, coordinated movement, and complex culture.
Terminology (Definitions and Uses)
Arboreal:
Living in trees.
Example: Chimpanzees have an arboreal life.
Stereoscopic vision:
Depth perception and understanding of object solidity.
Binocular vision:
Vision with both eyes, enabling depth perception.
Opposable thumb:
Thumb opposes the fingers; allows precision grip.
Foramen magnum:
Opening at the base of the skull through which the spinal cord passes.
Dentition:
Development and arrangement of teeth in the mouth.
Prognathous/prognathism:
Projection of jaws and nose leading to a pointed face (apish); humans are non-prognathous with a flatter face.
Hominid vs Hominin (recap):
Hominid: modern humans, chimpanzees, gorillas, orangutans, and their ancestors.
Hominin: modern humans and all extinct human species and our immediate ancestors.
Genetic and Archaeological Evidence for Common Ancestry
Genetic evidence:
Chromosomal DNA comparisons: Humans and chimpanzees share about 98.76 ext{ extperthousand} of base-pair sequence similarity.
Mitochondrial DNA (mtDNA): Used to infer timing of divergence and levels of variation.
Y-chromosome DNA provides complementary lineage information.
Archaeological evidence:
Fragments of sticks, burned bones, stone tools etc. indicate cultural complexity.
While chimpanzees use tools, humans uniquely use and manufacture tools in more sophisticated ways.
Notable Timeframes and Hominoid Genera (Contextual Overview)
Ardipithecus (earliest recognized hominid, ~5.8-4.4 ext{ MYA}):
Ape-like and australopithecine traits; probable bipedality; central foramen magnum; pelvis features; long arms; opposable big toe.
Brain capacity ~300-350 ext{ cm}^3.
Australopithecus (first bipeds, ~4.5-1.5 ext{ MYA}):
Bipedal with central foramen magnum; pelvis wide; long arms; fingers long and curved; brain ~380-500 ext{ cm}^3; diastema small; protruding jaw; slope of face; U-shaped palate; brow ridges.
Noted fossils: Taung child, Lucy (A. afarensis), Mrs. Ples (A. africanus), A. sediba.
Homo (appeared in Africa ~2.2 ext{ MYA}):
Key features: fully upright biped; foramen magnum directly above vertebral column; pelvis short and wide; arms shorter than legs; feet with non-opposable big toe; large brain up to 600-1400 ext{ cm}^3.
Notable species: Homo habilis (handy man), Homo erectus (upright man), Homo neanderthalensis (Neanderthals), Homo sapiens.
The San (Boskop-like discussion):
Greatest mtDNA diversity among living humans, indicating deep ancestry and long-standing presence in Africa.
Interpreting Human Evolution: Key Concepts and Connections
The brain-body size relationship and cognitive capabilities co-evolved with crude motor skills like tool use and language.
The shift to bipedalism freed hands for tool-making and transport, which in turn supported social complexity and cultural transmission.
Diet shifts (hard, raw foods to softer, cooked foods) likely influenced dental and facial evolution, jaw mechanics, and brain energy demands.
Genetic and fossil evidence together support a predominantly African origin for Homo sapiens with later spread to global populations; mtDNA and Y-chromosome data provide insight into timing and migration patterns.
The presence of transitional fossils and intermediate morphologies demonstrates that evolution is a gradual process with mosaic traits across lineages.
Practice Summary: Quick Reference
Hominid vs Hominin definitions and examples.
Major skull changes from ape-like ancestors to modern humans: foramen magnum position, cranial capacity, brow ridges, jaw shape, dentition, chin development.
Key fossil genera and their approximate timeframes: Ardipithecus (~5.8–4.4 mya), Australopithecus (~4.5–1.5 mya), Homo (~2.2 mya onward).
Evidence types for common ancestry: fossils, genetics (chromosomal mtDNA, Y-chromosome), archaeology (tools and culture).
The Out of Africa vs Multiregional hypotheses and their supporting evidence.
Practice question prompts (3.1 and 3.2 series) to test skull recognition, bipedalism advantages, and comparative anatomy.
Proteins of note: Brain sizes across species often quoted as ranges (e.g.,
Ardipithecus: $300-350\ \text{cm}^3$;
Australopithecus: $380-500\ \text{cm}^3$;
Homo habilis to Homo erectus: $600-1400\ \text{cm}^3$;
Modern Homo sapiens: $1200-1800\ \text{ml}$).
Important numeric reference: Humans and chimpanzees share roughly 98.76\% base-pair similarity in chromosomal DNA.
Quick Q&A Highlights (from slides)
Question: Identify whether A and B correspond to gorilla and human skulls. Answer: Gorilla vs Human skull features are used to distinguish.
Question: Which organism is primarily bipedal? Answer: The modern human (B in many diagrams).
Question: Name two advantages of bipedalism. Answer examples: mobility in open environments; freeing hands for tools/offspring; better thermoregulation.
Question: Name two similarities between skulls A and B. Answer examples: presence of upright posture traits, opposable thumbs, or stereoscopic/binocular vision.
Note: The slides include a number of exemplar diagrams (A, B, C) for skull comparisons and multiple-choice prompts. Use the relationships discussed here to study the features that distinguish Homo sapiens, Homo erectus, Australopithecus, Paranthropus, Ardipithecus, and Pan/Chimpanzee skulls. Remember to underline scientific names when required and to review the differences in dentition, cranial size, jaw shape, and foramen magnum position as core markers of human evolution.