1. HUMAN EVOLUTION
Option D.3
IB Biology
Miss Werba

2. OPTION D - EVOLUTION D.1 ORIGIN OF LIFE ON EARTH D.2
SPECIES AND SPECIATION
D.3
HUMAN EVOLUTION
AHL D.4
THE HARDY–WEINBERG PRINCIPLE
AHL D.5
PHYLOGENY AND SYSTEMATICS
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3. THINGS TO COVER Absolute dating using radioisotopes
Major physical features that define humans as primates
Trends in fossils of Australopithecus and Homo
Coexistance of species of the family Hominidae
Incompleteness of the fossil record
Correlation between the change in diet & increased brain size in hominid evolution
Difference between cultural & genetic evolution
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4. RADIOACTIVE DATING Command term = OUTLINE
Fossils contain isotopes of elements that have accumulated in the living organisms.
Isotope: an atom which has a different mass to the other atoms of the element, caused by a different number of neutrons within its nucleus.
If the isotopes are unstable, they will break down over time, changing into other elements and emitting radiation. This is called radioactive decay.
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5. RADIOACTIVE DATING Command term = DEFINE
Each radioactive isotope has a fixed half-life.
Half-life: The time it takes for half of a radioactive isotope to decay.
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6. RADIOACTIVE DATING Command term = OUTLINE
Radiocarbon dating:
Carbon-14 (14C) is an isotope of carbon (12C)
The two forms are maintained in constant proportions while an organism is alive.
When an organism dies, the proportion of carbon-14 begins to decrease.
The proportion of carbon-14 remaining can be used to identify the age of a sample.
Carbon-14 has a half life of 5,730 years
Carbon-14 is therefore only useful for dating fossils up to ~60,000 years of age.
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7. RADIOACTIVE DATING Command term = OUTLINE
Potassium/Argon dating:
Potassium-40 (40K) is an isotope of potassium (19K)
Potassium-40 is released in lava from active volcanos
As it decays, it transforms into argon-40 (a gas)
Potassium-40 has a half life of 1,300 million years
Potassium-40 is therefore useful for dating fossils over one million years of age.
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8. RADIOACTIVE DATING Command term = DEDUCE
10,000 years
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9. RADIOACTIVE DATING Command term = DEDUCE
Half life = the time taken for the amount of parental isotope to fall to half of its original level.
The half-life of Strontium-90 is 28 years, as there is only 50% of the parental strontium-90 isotopes remaining.
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10. THE ORDER OF THE PRIMATES Command term = DESCRIBE
There are several anatomical features that define humans as primates:
Opposable thumbs / grasping pentadactyl limbs
Forward facing eyes/binocular vision
Large brains relative to body size
Flexible shoulder joints (provide large range of movement)
Finger pads / nails not claws
Reduced snout leading to reduced olfaction
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11. THE ORDER OF THE PRIMATES Command term = DESCRIBE
Skull adapted for upright posture
rotating hand (pronation)
Tailless primate
Generalised dentition (different types of teeth)
Slower reproduction
Better visual acuity
Social dependency
Parental care
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12. HOMINID FOSSILS Command term = DESCRIBE
The word hominid refers to members of the family of humans, Hominidae.
This family consists of all species on our side of the last common ancestor of humans and living apes, including members of the Pongo (orang utans), Gorilla, Pan (chimpanzees) and Homo (humans) genera.
Homo sapiens is the only human species still in existence.
The fossil record is incomplete but there is enough to give a good outline of the evolutionary history of humans.
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13. HOMINID FOSSILS Command term = DESCRIBE
You are expected to be able to describe the trends across the following species:
Ardipithecus ramidus
Australopithecus afarensis
Australopithecus africanus
Homo habilis
Homo erectus
Homo neanderthalensis
Homo sapiens
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14. D.3.5 14

15. HOMINID FOSSILS Command term = DESCRIBE
Ardipithecus ramidus (Ar. ramidus):
First discovered in 1994
One of the earliest fossils found so far – nicknamed “Ardi”
Approx. age: 5.2–4.4 million years
Distribution: Ethiopia
Size: ~120 cm tall and ~50 kg
Brain capacity: ~375–550cm3, about the size of a chimp
Features:
It was bipedal on the ground and quadrupedal in the trees.
It lived in a woodland environment
Diet consisted of fruit, leaves and insects
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16. HOMINID FOSSILS Command term = DESCRIBE
Australopithecus afarensis (A. afarensis):
Most complete skeleton found – nicknamed “Lucy”
Approx. age: 4.0–2.5 million years
Distribution: Ethiopia and Tanzania (south & east Africa)
Size: height ~ cm and weight ~29-42kg
Brain capacity: ~380–430cm3
Features:
It was bipedal, leaving their hands free
They had an ape-like face
Diet was more omnivorous
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17. HOMINID FOSSILS Command term = DESCRIBE
Australopithecus africanis (A. africanis):
It is similar to A. afarensis
Started moving on to the savannah and out of the trees
Approx. age: 3.2–2.5 million years
Distribution: south & east Africa
Size: height ~ cm and weight ~30-41kg
Brain capacity: ~435–530cm3
Features:
It was bipedal
Larger molars for plant based diet
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18. HOMINID FOSSILS Command term = DESCRIBE
Homo habilis (H. habilis):
Nickname – the “handy man”
Used stone tools
Approx. age: 2.4–1.6 million years
Distribution: south & east Africa
Size: height ~ cm and weight ~32kg
Brain capacity: ~700cm3
Features:
Smaller teeth and jaw for meatier diet
Reduced brow ridge
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19. HOMINID FOSSILS Command term = DESCRIBE
Homo erectus (H. erectus):
Java man and Peking man were both H. erectus fossils
Suspect that they had use of fire and very basic language
Approx. age: 1.8–0.1 million years
Distribution: north, south & east Africa, west & east Asia
Size: height ~ cm and weight ~40-68kg
Brain capacity: ~880cm3
Features:
Thick skull bones
External nose
Meat a significant part of diet
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20. HOMINID FOSSILS Command term = DESCRIBE
Homo neanderthalensis (H. neanderthalensis):
Nickname – “Neanderthal man”
Lived in caves
Approx. age: 200,000–30,000 years
Distribution: Europe, west Asia
Size: height ~ cm and weight ~54-65kg
Brain capacity: ~1500cm3
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21. HOMINID FOSSILS Command term = DESCRIBE
Homo neanderthalensis (H. neanderthalensis):
Features:
Neanderthals mostly lived in cold climates. Their bodies were short and solid, with short limbs – adapted to the cold.
Their bones are thick and heavy, with powerful muscle attachments – they would have been very strong.
A large number of tools and weapons have been found
Neanderthals were good hunters.
Neanderthals were the first people known to have buried their dead, indicating that they had ideas about the afterlife.
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22. HOMINID FOSSILS Command term = DESCRIBE
Homo sapiens (H. sapiens):
Approx. age: 140,000 - present
Distribution: worldwide
Brain capacity: ~1440cm3
Features:
a sharply rising forehead
flatter face
small eyebrow ridges
a prominent chin
a light bone structure
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23. HOMINID FOSSIL TRENDS Command term = DESCRIBE
More downward facing foramen magnum (bipedalism)
S-shaped curvature of the spine (erect posture)
Lower and broader pelvis (bipedalism)
Shorter arms and longer legs (bipedalism)
Increased size of heel bone and alignment of big toe (bipedalism)
Flatter faces, with reduced brow ridges and jaw protrusion
Larger cranial capacity with increased brain size (greater intellectual prowess)
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24. HOMINID FOSSIL TRENDS Command term = DESCRIBE
Smaller teeth and jaws more V-shaped (changing dietary requirements – more meat, less vegetation)
Marked reduction in body hair
Shift in muscle groups (bipedalism)
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25. HOMINID FOSSILS Command term = DESCRIBE / STATE
There are some periods of overlap!
(there are also species missing from timeline that are not required for exams)
H. sapiens
H. neanderthalensis
H. erectus
H. habilis
A. africanus
A. afarensis
Ar. ramidus
millions of years ago
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26. HOMINID EVOLUTION Command term = STATE
At various stages in hominid evolution, several species may have coexisted.
Homo habilis may have co-existed with various species of Australopithicus
Homo neanderthalensis likely co-existed with Homo sapiens
Some propose that Homo sapiens hybridised with Homo neanderthalensis .
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27. INCOMPLETENESS OF THE FOSSIL RECORD Command term = DESCRIBE
Fossilization is a rare occurrence.
Most components of dead organisms decompose relatively quickly following death.
Fossilization tends to favour hard body parts.
Exposed fossils are soon destroyed/weathered, reducing the chance of them being found;
Fossilization favours species that lived for a long time.
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28. INCOMPLETENESS OF THE FOSSIL RECORD Command term = DESCRIBE
Very few fossils have been found so picture is incomplete
Individual fossils may not be representative of species (ARE YOU?!?!!)
Very few complete skeletons have been discovered
Relies on a relatively small amount of data to draw conclusions.
New discoveries regularly come to light, leading scientists to re-interpret previous assumptions in the light of the new data.
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29. RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS
What are the benefits of a bigger brain?
Higher order thinking – like planning, hunting, inventing
More complex tools
Mastery of fire – for cooking, warmth, protection
Ability to learn and pass on knowledge to the next generation to improve survival chances
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30. RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS
What are the costs of a bigger brain?
Longer gestation period
Longer period of development until they are self- sufficient
Large period of brain development post-birth
Energetically expensive!
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31. RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS
Tool making first associated with H. habilis.
This would have required a larger brain.
Larger brain requires vast amounts of energy, creating a demand for changes in diet.
Changing to a higher calorie diet may have allowed further increase in brain size.
Animal tissues (meat) can provide the necessary structural lipid for human brain expansion.
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32. RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS
As brain size increased, language and cognitive abilities also developed.
Larger brain also allowed for better hunting and gathering, increasing the calorie intake even further.
Changes in the dental fossil record are indirect evidence for such a change in diet.
The increase in brain size in hominid fossils has been closely correlated with an increased intake of meat.
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33. CULTURAL & GENETIC EVOLUTION Command term = DISTINGUISH
Is controlled by genes.
Limited by the genotypes of the populations.
Controlled by natural selection and selective advantage.
eg. increase in cranial capacity in hominids
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34. CULTURAL & GENETIC EVOLUTION Command term = DISTINGUISH
Cultural evolution:
Based on skills/info passed from one generation to another
New skills/info can be transmitted between different groups
It is learned/taught.
It is language dependent.
Only possible because of large brains of the Homo species allow for learning.
Allows more rapid evolution.
eg. tool making, religion, art
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35. RECENT HUMAN EVOLUTION Command term = DISCUSS
Changes in genotype have lead to cultural evolution in humans by promoting intelligent behaviour.
Larger brain sizes have promoted increased learning/thinking capacity.
Prolonged gestations have promoted social interactions and family networks.
Bipedalism has promoted extensive migration and improved socialisation.
Shorter finger bones and reduced reliance on forelimbs for locomotion have promoted increased tool manipulation.
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36. RECENT HUMAN EVOLUTION Command term = DISCUSS
Evolution of culture (eg. art, science, language) has been more rapid and recent than genetic evolution (which requires many generations).
Further cultural evolution (through genetic engineering and reproductive technology) may hasten changes in our genetic evolution.
Certain products of cultural evolution (eg. medicines) may reduce genetic evolution via natural selection.
Other products of cultural evolution (eg. pollution) may increase genetic evolution (increased mutagenic rate).
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37. Sample questions a) Outline a method for dating fossils using 14C. [2]
Q1 (5 min)
a) Outline a method for dating fossils using 14C. [2]
b) Outline the trends illustrated by the fossils of Ardipithecus and Australopithecus. [3]
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38. Sample questions
Q2 (4 min)
Outline, using named hominid fossil species, trends in hominid skull evolution. [3]
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39. Sample questions A1
a) most carbon is 12C but there is small amount of (radioactive) 14C; organisms absorb the same ratio of 12C:14C as in the environment; after death, no more atoms accumulate; 14C steadily breaks down so amount decreases/ half-life (~5730 years); the less 14C in a sample the older the fossil / 14C useful for dating samples suitable for fossils 1, ,000 years old; [2]
b) Ardipithecus is an older genus (5.2–4.4 million years ago) than Australopithecus (4–2.5 million years ago);
toe structure shows that both genera were probably bipedal;
tooth structure changed as diet changed from soft fruits/leaves/seeds/
nuts to omnivorous diet;
large canines seen in Ardipithecus to smaller canines in Australopithecus;
increasing height —Ardipithecus is smaller (the size of a chimpanzee);
change in face from projecting to flat face / from tall to small lower
jaw / development of high forehead / loss of brow ridges; [2]
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40. Sample questions Q2
Australopithecus afarensis (A. afarensis) had a relatively small skull
with a low forehead/moderate sized brow ridges;
A. Africanus (and A. robustus) evolved from A. afarensis with increases
in cranial capacity/larger brow ridges/low forehead;
Homo habilis (H. habilis) had a small cranial capacity/small brow
ridges/increased forehead;
H. erectus/H. neanderthalensis/H. sapiens followed H. habilis
and show increased cranial capacity;
As the Homo sp evolved, the forehead increased;
As the Homo sp evolved, the orbital ridges decreased; 3 max
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