IB Biology Review
Human Evolution
Taxonomy of Humans
Kingdom:
Phylum:
Class:
Order:
Family:
Genus:
Species:
Animalia
Chordata
Mammalia
Primate
Hominidae
Homo
Sapiens
Chronological Line of Human Evolution
Australopithecus afarensis
Australopithecus africanus
Australopithecus robustus
Homo habilis
Homo erectus
Homo sapiens
Which species are alive?
Only Homo sapiens
Biochemical Evidence for
Human Evolution from Apes
similar amino acid sequence
similar DNA sequences
remember, chimpanzees share 98% of their
genes with humans
Anatomical Evidence for
Human Evolution from Apes
Both humans and apes have
grasping limbs
opposable thumb
stereoscopic vision
retention of juvenile features (hairless at birth)
similar cranial features
no tail
rotatable shoulder joint
What four physical traits
define humans as primates?
Have opposable thumb / power grip
Have well developed cerebral cortex / brain
Have limber shoulder joints
Have finger pads / fingerprints / nails (not
claws)
When did bipedalism come about?
bipedalism evolved in hominids
about 5 million years ago
fossil footprints found
(at Laetoli) 3.6 million years ago
anatomy of hominids suggests
bipedality at 4.4 million years
ago
How did bipedalism change
the life of early hominids?
bipedality provides greater field of view for
foraging, detecting predators or traveling
bipedality is an efficient way to move
bipedality frees hands for manipulation
Which anatomical features
help humans to be bipedal?
arches on feet
support weight and absorb shock
stronger bones in legs / stronger legs
allows for all the weight to be carried by two limbs
instead of four
longer legs
bigger stride, more efficient to walk
shorter arms
long arms not needed to help individual move
non-opposable big toe
supports weight distribution in foot
Which anatomical features
help humans to be bipedal? cont.
foramen magnum
positioned at back and bottom of skull so head can be held
upright and still be balanced
knees closer together
enabled smooth stride
wide pelvis
enabled leg bones to fit into to hips to allow bipedalism
lumbar spine curved
absorbs shock from each step
larger muscles on legs
powered two limbs to move body instead of four limbs
Position of the Foramen Magnum
Humans
Directly under head
Resting above spine
Humans stand straight up,
don’t need spine to be angled
into head
Ape
Towards back of head
Spine slanted into head
Apes don’t stand straight up
How was Australopithecus afarensis
the prototype human?
Had non-opposable big toe
Had a broad pelvis
Had more vertical posture
Skull on top of vertebrae
Long legs indicating bipedality
Curved finger bones meaning it was still living
in trees
Why did Australopithecus
start walking on two legs?
Environment changed
It used to live in dense forest
Drought killed off forest
Became savannah
Had to leave trees
Had to travel far distances to
get food and water
What is genetic evolution?
Evolution through variation and inheritance of
genes
Changes the physical features of the body
What is cultural evolution?
Evolution through customs like languages, etc.
that are taught/learned
Why does cultural evolution
depend on increases in brain size?
Organisms can’t use a part of the brain that
isn’t there!
The new parts of the brain (neocortex) deal
mostly with language and art
Language and art could not be developed
before the brain capacity was there
IB Exam Question
1. State the order, class, family, genus and
species of human beings.
(1 mark)
Order: Primate
Class: Mammalia
Family: Hominidae
Genus: Homo
Species: sapiens
IB Exam Question
2. Discuss the anatomical and biochemical
evidence which suggests that humans
arose from a species of ape.
(6 marks)
biochemical evidence:
similar amino acid sequence (e.g. cytochrome,
hemoglobin);
similar DNA sequences;
anatomical evidence:
grasping limbs;
opposable thumb;
stereoscopic vision;
retention of juvenile features (hairless at birth) /
neoteny;
similar cranial features;
no tail;
rotatable shoulder joint;
IB Exam Question
3. State four major physical features
which define humans as primates. (4 marks)
opposable thumb / power grip;
well developed cerebral cortex / brain;
limber shoulder joints;
finger pads / fingerprints / nails (not claws);
IB Exam Question
4. Discuss the origin and consequences of
bipedalism in hominids.
(4 marks)
Origins:
bipedalism evolved in hominids about 5 Mya;
fossil footprints found (at Laetoli) 3.6 Mya;
anatomy of hominids suggests bipedality at 4.4 Mya;
but the fossil record is limited before this date;
bipedality possibly associated with a change in habitat
/ climate / woodland to savannah;
Consequences:
bipedality provides greater field of view for foraging /
detecting predators;
bipedality is an economical form of locomotion
bipedality frees hands for manipulation / carrying
things / gesture;
IB Exam Question
5. Discuss the anatomical features that
enable bipedalism in humans. (3 marks)
arches on feet;
stronger bones in legs / stronger legs;
longer legs;
shorter arms;
non-opposable big toe;
foramen magnum;
knees closer together;
wide pelvis;
lumbar spine curved;
larger muscles on legs;
IB Exam Question
6. Outline the trends illustrated by the
fossils of Australopithecus afarensis. (3 marks)
non opposable big toe / broad pelvis / more
vertical posture / skull on top of vertebrae;
short legs indicating bipedality;
curved finger bones / phalanges;
indicating it was still arboreal;
dentition more like a chimp / larger canines /
parallel molars;
IB Exam Question
7. Discuss the possible habitat of Australopithecus
and the ecological changes that might have
prompted its origin.
(3 marks)
about five million years ago;
it became drier;
it became cooler;
dense forest was replaced by thin woodland /
clearing;
evolution of bipedalism (started leaving trees);
vegetarians;
incompleteness of fossil record causes
uncertainties about human evolution;
IB Exam Question
8. Outline the difference between genetic
and cultural evolution.
(2 marks)
genetic evolution through variation and
reproduction / inheritance of genes;
cultural evolution through customs /
languages, etc. taught/learned;
IB Exam Question
9. Discuss how cultural evolution in humans
depended on increases in brain size. (3 marks)
large brain size correlates with language;
large brain correlates with improvements in
tool-making
improved tools allow more nutritious diets for
further brain development (especially hunting
tools);
increased brain size leads to written history /
cave art / symbolic thought;
IB Exam Question
10. Discuss the relative contributions of genetic
and cultural evolution in the evolution of humans.
(6 marks)
In genetic evolution, the unit of genetic inheritance is the gene;
genetic evolution leads to changes in anatomy/physiology;
such as large brain / bipedality / other example;
unit of cultural inheritance is word /gesture /image /symbol /language /tool;
culture is largely acquired / Lamarkian;
genetic inheritance is Darwinian;
cultural evolution linked to technology / cultural revolutions (e.g.
agriculture);
both genetic and cultural evolution allow humans to rise above
environmental limiting factors such as food / water / shelter / disease;
cultural evolution more rapid than genetic evolution;
genetic evolution still occurring (through changes in allele frequency
due to differential reproductive rates of certain races);
e.g. sickle cell anaemia and resistance to malaria / HIV resistance / other
example;
genetic inheritance precedes cultural evolution;
brain size increases through genetic evolution enabling cultural evolution;
IB Exam Question
11. Explain why the approximate date and
distribution of H. habilis are uncertain. (3 marks)
2 (±0.5) million years ago in (sub-Saharan)
Africa;
uncertain because
fossils lacking or not in good form;
soft parts do not fossilize;
interbreeding of species;