HUMAN EVOLUTION 26 AUGUST 2015

Section A: Summary Content Notes

Evidence of common ancestors for living primates, including humans

We looked at the use of fossils as evidence for evolution in the previous chapters.

We can now use that knowledge to explain the origin of modern humans

Humans share a common ancestor with two closely related groups of African apes, namely

chimpanzee and bonobos. This common ancestor lived about seven million years ago and

gave rise to humans and their direct ancestors (homnins)

A common ancestor is an ancient species that gives rise to two or more new species. The

new species are descended from the common ancestor.

The phylogenetic tree below shows that gibbons, gorillas , orang-utans, chimpanzees and

humans descended from a common ancestor that lived 35 million years ago

Scientists use different kinds of evidence to construct a phylogenetic tree.

One kind of evidence is to compare anatomy of two closely-related living species.

Similarities in the anatomy were probably present in the ancestor

Differences have evolved since the common ancestor divided into two new species

A phylogenetic tree for apes

and humans

Anatomical similarities between African apes and Humans

Enlarged and more complex brain relative to body size

Reduced snout with reduced sense of smell

Eyes in front of skull- stereoscopic vision

Eyes have cones

Two hands – five digits

Mobile opposable thumbs

Digits with flat nails

Long, slender limbs that rotate freely at shoulders and hips

Sexual dimorphism –male and female clearly distinguished

Have molars and premolars with rounded cusps

Anatomical differences between African apes and Humans

When we look at the differences you must be able to compare the following:

o Bipedalism (foramen magnum, spine and pelvic girdle)

o Brain size

o Teeth (dentition)

o Prognathism

o Palate shape

o Cranial ridges

o Brow ridges

o

There are three main lines of evidence that that indicate hominids have a shared common

Fossil evidence

Genetic evidence

Cultural evidence

1. Fossil evidence Palaeontologists study fossils to provide more information about structure,

movement, lifestyle, and environment

In search for a common ancestor for hominids , palaeontologists look at the

following features

Bipedalism

Dentition (teeth)

Palate shape

Brain size

Prognathism

AFRICAN APES HUMANS TYPE OF MOVEMENT

Quadrupedal – knuckle-walkers/

walk on all fours

Bipedal – walk upright on two legs

Foramen magnum at back of skull Foramen magnum closer to front of

the skull

C-shaped vertebral column S-shaped vertebra column

Long and narrow pelvis Short and wide pelvis

BRAIN SIZE

Smaller less developed brain Large well developed brain

TEETH (dentition)

Large prominent canines Smaller canine

Thin tooth enamel Thick tooth enamel

PROGNATISM

Large prominent jaw bone with no

chin (prognathism)

Rounded jaw with developed chin

Wider, sloping face Narrow flat face

PALATE SHAPE

Narrow rectangular palate Wider more curved palate

CRANIAL and BROWRIDGES

Prominent cranial and brow ridges Reduced cranial and brow ridge

2. Genetic evidence

DNA comparisons are made between living hominids , as DNA breaks

down in dead cells and its very rare to extract DNA from a fossil

Organisms have two types DNA

o Chromosomal DNA – in the nucleus

o Mitochondrial DNA (mt DNA in the mitochondria)

3. Cultural evidence Tools – Oldowan, Acheulian, Mousterian

Fire-making, burial rites, art and hunting techniques

Development of speech and language

MAJOR PHASES IN HOMINID EVOLUTION Humans and their fossil ancestors between the common ancestor and modern

humans are classified as hominids

The three main genera (phases) of human evolution are:

Ardipithecus

Australopithecus

Homo

Section B Practice Questions

Question 1 (Taken from DBE Feb-March 2013 Paper 1)

Professor Lee Berger and his colleagues studied the fossils they found in a cave at the Cradle

of Humankind. The skeletons from the cave are ranked amongst the most complete finds to

date. The adult female, Australopithecus sediba, was remarkably well preserved and some

of the following characteristics were identified:

Images showing the structure of the skull and bones of the palm of A sediba

1.1. Write down THREE characteristics from the list above that also apply to the Homo

species. (3)

1.2. State TWO advantages of A. sediba being bipedal. (2)

1.3. Professor Berger called Australopithecus sediba a transitional fossil. Using the

information in the list above, explain why he called A. sediba a species in transition. (2)

Question 2 (Taken from KZN Prelim Paper 1 2012) The diagrams below show the skull capacity of extinct hominid species and the time they

occurred

2.1. Draw a bar graph to compare the skull capacity of the above hominid species (6)

2.2. What trend can be observed from the graph above? (3)

2.3. Describe TWO visible differences between A. Afarensis and H. Sapiens. (4)

2.4. List FOUR characteristics that humans share with other primates. (4)

2.5. Homo sapiens are considered to be the most developed species. Although

Homo neantherthalensis has a brain capacity of 1 500cc Homo neantherthalensis

is extinct but Homo sapiens are still in existence. Explain how this is possible. (3)

Question 3 (Taken from DBE Exemplar Paper 1 2011)

Diagrams A and B below illustrate the skulls of Homo sapiens and Homo erectus. The diagrams are drawn to scale.

3. 1 Which of the diagrams (A or B) represents the following:

a. Homo sapiens b. Homo erectus (2)

3. 2 Tabulate TWO visible differences between the skulls in diagrams A and B that

represent changes in the structure that characterises human evolution. (5)

Question 4 (Taken from DBE Nov Paper 2 2010)

Study the diagrams below of the upper jaw, skull and the foot of two organisms A and B.

The diagrams are NOT drawn to scale.

4. 1 With regard to the drawings above:

a. Tabulate TWO visible differences between the upper jaws of organisms A and B

(5)

b. Name ONE visible difference between the feet of organisms A and B. (2)

4. 2 Which organism (A or B) is more likely to be bipedal? (1)

4. 3 Give a reason for your answer to question 4.2. (2)

Question 5 (Taken from DBE Feb-Mar Paper 1 2012)

The diagram below represents a cladogram (phylogenetic tree) showing primate evolution.

The letters, A to E, indicate the characteristics which are shared by the different species of

primates which follow the letter. The point where various species of primates differ from

each other is indicated by the branching-off/split into new species.

5.1. Which LETTER represents a common characteristic of all primates? (1)

5.2. List THREE structural characteristics represented by the LETTER named in QUESTION

(3)

5.3. Which organism is most similar to the chimpanzee? (1)

5.4. Name any TWO structural characteristics of the skull that make the organism named

in QUESTION 5.3 different from the chimpanzee. (2)

5.5. Write down the names of the organisms that display the characteristic C but not

characteristics D and E. (2)

Question 6 (Taken from DBE Nov Paper 1 2013)

Describe the structural changes to the skull that characterise the evolution of modern

humans from their ape-like ancestors, and explain the significance of these changes.

(20)

Section C: Solutions

Question 1

1.1. Projecting noseSmaller canines Bipedal

1.2. They had a wider view to spot danger

They could carry offspring/food/tools

Large surface area for thermoregulation

1.3. Have characteristics of both Homo species and Australopithecusspecies

Question 2

2.1.

2.2. The younger the skull, the larger he skull capacityOR

The older the skull, the smaller the skull capacity

2.3

2.4. Enlarged and more complex brain relative to body size

Reduced snout with reduced sense of smell

Eyes in front of skull- stereoscopic vision

Eyes have cones

Two hands – five digits

Mobile opposable thumbs

Digits with flat nails

Long, slender limbs that rotate freely at shoulders and hips

Sexual dimorphism –male and female clearly distinguished

Have molars and premolars with rounded cusps

2.5. Did not have a languagetherefore could not communicate unlike Homo sapiens

that had a lanugauge and could comminicate

Homo sapiens had the ability to inhabit different environments to suit their needs

unlike Homo neanderthalensis who could not and therefore became extinct

Question 3

3.1 a. B b. A

3.2

Diagram A Diagram B

Smaller brain capacity Larger brain capacity

Brow ridge pronounced Brow ridge not as pronounced

Lower jaw had a poorly developed chin Lower jaw has a much better developed

chin

Question 4

4.1

b Differences in Feet

In A the big toe is close to the other 4 smaller toes/faces forward

In B the big toe is apart/opposable from the other 4 smaller toes/points outwards

OR

In A the heel bone is relatively larger and in B it is relatively smaller

OR

In A the bones in the foot are straight and in B they are curved

OR

In A phalanges are relatively shorter and in B they are relatively longer

4.2 A

4.3 Foramen magnummore towards the centre of the skull in A/ more forward

OR

In B the foramen magnum more towards the back of the skull

Question 5

5.1. A

5.2. Opposable thumbswith power and precision grip

• Bare fingertipswith nails

• Long arms

• Freely rotating arms

• Eyes in front

• Stereoscopic vision

• Eyes with cones

• Large brain size compared to body mass

• Two mammary glands

• Sexual dimorphism

• Olfactory brain centre reduced

5.3. Humans

5.4. Shift in the position of foramen magnumto a forward position

• Gently curved jaws

• Flat face

• Well developed chin

• Not prognathus

• Forehead less sloping

• No pronounced brow ridges

• Smaller canines

• Spaces between teeth bigger

• Larger brain size

5.5. Rhesus monkey Gibbon

Question 6