Human Evolution: Evidence of Common Ancestors

KNOWLEDGE AREA:

Diversity, Change and

Continuity

TOPIC 4.2:Human Evolution

Evidence of Common Ancestors

for Living Hominids including

Humans



Before we look at the 

phylogenetic tree 

we must

first study the  

classification of humans

.



Humans are found in the 

class mammalia

.



They belong to the 

order Primates 

and then



They are found in the 

sub-order Anthropoidea



This 

sub-order

 is made up of 

2 families

.



These are 

family Hylobatidae

, and 

family

Hominidae

.



Humans fall into the 

family Hominidae

.



Then 

genus Homo



Finally 

species Homo

sapiens



This is all shown in the

picture alongside.



Here we often come

across the terms

hominid and hominin

.



Lets look at these 2

terms.

Classification of Humans



Hominid

 refers to the 

group

 which 

contains

modern humans, chimpanzees, gorillas and

orangutans

.



It also 

includes all their immediate ancestors

.



In other words 

all the organisms 

found in the

family Hominidae

.



Hominin

 refers to 

modern humans 

and 

all

the extinct human species

.



It also 

includes all our immediate ancestors

.



Now will look at how the 

humans are similar 

and

different to the African apes

.



The 

African

apes 

include the

gorillas, chimpanzee

and bonobos

.

Now lets look at the

phylogenetic tree

.

Chimpanzee

Bonobos



The phylogenetic trees on the next 2 slides gives

some information on human evolution.



We will use both these trees to trace human

evolution from about 6 million years ago.



Between  

6 to 7 mya the first bipedal primates

appeared.

These organisms had the following features:

a.

Small brain size

b.

Foramen magnum had a forward position.

c.

Small canine teeth



Then about 

4mya 

Australopithecus 

appeared.



They had 

features of both primitive apes 

and

modern humans

.



They had the 

head of primitive apes 

and from the

neck down they looked like the modern humans

.



Therefore they are 

often called ape-men

.

The features  shared

with primitive

apes were

…

1.

Protruding jaws

2.

Heavy brow ridges

3.

Slopping faces

4.

Small brain.

Australopithecus



A 

new genus

appeared between

4.32 and 4.51 million

years ago

.



This was the

Ardipithecus

.



This 

genus

 was made

up of 

2 species

.



They were 

A. ramidus

and 

A. kadabba



A. kadabba 

lived

about 

5.6 mya

.

A. ramidus

A. ramidus 

had the following features…

1.

A small brain

2.

A pointed face and poorly developed chin

3.

A grasping big toe for swinging from branch to

branch of trees.

4.

It was also adapted for bipedalism.



Then about 

2 mya the australopithecines 

gave rise

to 

Homo habilis 

(the handy man)



H. habilis 

was referred to as the 

handy man 

because

fossil evidence showed that they used tools

.



H. habilis 

was 

first of the early humans

.

H. habilis 

was different from the australopithecines in

the following way…

1.

Less pronounced

brow ridges

2.

More human like

teeth

3.

A flatter face

4.

A more rounded

head

5.

A brain capacity of

600 to 750ml.

homo habilis



It is thought that

about 

1.5 mya 

H.

habilis 

gave rise to

Homo erectus

.



H. erectus 

had the

head of an ape 

but

from the neck down it

looked like modern

man

.



It  was 

as tall as

modern man 

and had

a 

larger brain size of

700 ml to 1300ml

.

Homo erectus



Then about 

150 000 to 200 000 

years ago 

h.

erectus

 gave rise to 

Homo sapiens

.



We will look at these in a little more detail later

on.



Two groups 

of the 

African apes 

share a 

common

ancestor with humans

.



These 

2 groups of apes 

are the 

chimpanzee and

bonobos

.

We want to look at evidence that support the idea of a

common ancestor.



We look at 3 lines of evidence.

These are …



Fossil evidence



Genetic evidence



Cultural evidence

Lets look at each of these in some detail.

1.

Fossil Evidence:



From our earlier discussion we can see that

many hominin fossils 

have been discovered over

the years.



Hominin fossils 

belong to 

at least 20 species

.



These 

fossil provide evidence 

for a 

close

evolutionary relationship

between humans and

the great apes

.



The 

fossils use anatomy 

to show this

relationship.



The 

fossils provide 2 lines of evidence

.

These are…

a)

Transitional fossils:



This refers to the 

immediate  fossils between a

group and their ancestor

.



In this case the 

transitional fossils 

have

characteristics of both the apes and humans

.



The 

great –ape characteristics 

are also found in

the common ancestor

, but



The 

human characteristics occur only 

in the

hominins

.

b)

The Oldest fossils:



These fossils have 

more characteristics of the

great apes 

than the 

younger fossils

.



These 

younger fossils 

are 

more like the modern

human

.



Over a period of time 

we see that the 

fossils

become more human like than ape like

.



We shall look at the 

similarities and differences

between the great apes and humans 

a little

later.

2.

Genetic Evidence:



The 

DNA base pairing 

of 

humans and the Great

apes

 are 

almost identical

.



The 

human DNA sequence 

is 

most similar 

to the

chimpanzee

.



Humans and chimpanzee 

have 

98.76%

 of

the 

base pair sequence in common

.



Since 

DNA sequence is so similar 

it 

provides

evidence for a close relationship between

humans and chimpanzees

.

3.

Cultural Evidence

:



Fragments of sticks, burned bones, stone

weapons and tools 

etc, were used as 

cultural

evidence for human evolution

.



Chimpanzees also use tools 

, for example using

stones to open nuts

.



Young chimpanzee learn behaviour 

from

watching their mothers

.



Therefore it is believed that the 

common

ancestor of humans and chimpanzee 

also 

used

similar tools in a similar way

.



Many of the 

early mammals lived on trees

.



Many

 of the 

African apes 

are 

still adapted 

for an

arboreal life

.

Humans share the following characteristics with

the African apes and other primates…

1.

The upper limbs

2.

The brain

3.

Vision

4.

Number of Offspring

5.

Upright posture

1.

The Upper Limbs:



Primates

 have 

very long arms

, which 

they move

freely

.



They are able to 

move their arms freely because

…

1.

The 

socket

 is 

very shallow

.

2.

The 

scapula is not attached 

to the 

vertebral column

.



They 

do not have claws

, instead 

they have flat nails

.



Their 

fingertips are bare 

and 

contain a large

amount of nerve endings

.



Finally all 

primates have opposable thumbs

.



The 

long arms 

are 

used to gather fruit 

from the

tips of tree branches

.



Their 

bare fingertips 

are 

very sensitive

, this

makes 

precision work possible

.  Therefore they

are able 

to make and use tools

.



The 

opposable thumbs 

makes the 

power grip and

precision grip possible

.



Like primates humans have…



 opposable thumbs,



flat nails instead of claws and



freely moving upper limbs.

2.

Brain:



We find that when we 

compare the brain to

body size

, the 

primates have large brains

compared to their body size

.



This 

enables them 

to 

process large amounts of

information

.



Parts of the brain responsible 

for 

interpretation

information coming from the hands 

and 

eyes

are enlarged

.



The 

olfactory organ 

is 

much reduced 

because

primates do not depend 

on the 

sense of smell

.

3.

Vision:



Their 

eyes are found 

in the 

front

.



They display both 

stereoscopic and binocular

vision

.



They have 

rods and cones 

to 

enable a more

clear and colour vision

.

4.

Number of Offspring Produced:



Primates 

produce far less offspring

.



Parental care 

is 

intensive

.

5.

Upright Posture

:



They have an 

upright posture

, which 

allows for

the primates to walk on two legs

.



This allows for 

better view of the surroundings

.



Upper limbs are free for carrying things 

such as

food, babies and tools.



List the characteristics that humans share with the

African apes.

1.

Large brains compared to their body mass.

Therefore a large skull.

2.

Reduced sense of smell due to a reduced olfactory

center in the brain

3.

Parts of the brain that process information from

hands and eyes are larger.

4.

Retina contains cones to make color vision possible.

5.

Stereoscopic vision

6.

Binocular vision

7.

Long upper arms

8.

Upper arms – full and free movement

9.

Forearm can rotate because of elbow joint

10.

No claws, nails are flat

11.

No hair on fingertips-bare fingertips

12.

Opposable thumbs

13.

Upright posture.

This is a good learning tool use it to learn the

similarities.



Anatomy 

refers to 

structural make up 

of an organism.



In this section we will look at how the humans and

African apes are structurally different from each other.

The following anatomical differences occur between

the humans and the African Apes…

1.

Bipedalism

2.

Brain size

3.

Dentition

4.

Flat face/Prognathism

5.

Cranial ridges

6.

Brow ridges



There is 

fossil evidence to support these anatomical

differences

.

Now lets look at each of these in some detail

1.

Bipedalism:



The 

African apes sit upright 

and are 

able to walk on

2 feet

.



However 

they do this 

only sometimes

,

while 

humans walk on 2 legs 

all the time

.



Animals that show 

bipedalism

 have 

a different

arrangement of the vertebral column 

to the 

head



Therefore the 

position

of the foramen magnum

had to 

change

.



It moved from the 

back

of the skull to a forward

position at the bottom

of the skull 

as shown

alongside.



This means that in

animals that show

bipedalism

, the 

foramen

magnum is in a forward

position at the bottom

of the skull,

 while

Position of Foramen Magnum



The animals that show 

quadrupedalism

 have a

foramen magnum at the back of the skull

.



In addition 

animals

with bipedalism 

had a

much wider and

shorter pelvis

,

because the 

pelvic

girdle had to support

the weight of the

body

.



While 

quadrupeds

have long, narrow

pelvic girdles

.

Comparison of pelvic girdle of

human and chimpanzee



Finally the 

spine of

an organism 

with

bipedalism

 is

straighter

 than a

quadrupedal

.

Comparison of the Spine

2.

Brain Size:



Over the time the 

brain size of the hominin

species has gradually increased

.



Homo sapiens 

have a 

brain size twice 

that of

Homo habilis

.



The 

brain size of the first bipedal apes 

was 

half

the size of the brain of 

Homo habilis

.



The 

brain of the modern man 

is the 

biggest

.



It 

ranges in size 

from 

1200ml to 1800ml

.



The 

advantage of the large brain size compared to

their body masses over those apes

 that had a 

smaller

brain compared to their body mass size is greater

intelligence

.



But it must be noted that this 

does not apply to

modern humans

.



Since humans have a 

larger brain they also have a

larger skull

.

3.

Dentition:



Apes have 

large canines that protrude

.



In 

humans

 the 

canines are much smaller 

and is

shaped almost like an incisor

.



The 

incisors in humans do not stick out

, while in

chimpanzees they stick out spatulas or spoons

.



The dental formula a of humans is 

2.1.2.3

2.1.2.3



The dental formula of the oldest primates are

2.1.3.3

2.1.3.3



The 

apes

 have a 

u-shaped jaw 

with 

parallel sides and

the front is slightly rounded

.



The 

incisors are found at the front and canines

,

premolars and molars are on the side

.



Humans

 have a 

gently curved jaw

.

4.

A flat face / Prognathism:



Modern humans have a 

flat face

.

The following features ensures that humans have a

flat face…

1.

The 

foreheads 

of 

modern humans do not slope

backwards 

while the 

forehead of the ape men

slope backwards

.

2.

Humans have  a well developed chin 

on their

lower jaws

.  

Human chins 

are 

square shaped

,

this is thought to be an 

adaptation for speech

.

Chimpanzees

 have 

rounded chins

.

3.

The 

bones of the nose and jaws stick out 

in the

ape man 

in other words ape men were

prognathous

.  Modern humans are 

not

prognathous

, this means that the 

bones of the

nose and jaws do not stick out

.



Humans have 

shorter palates than apes

.



The chimpanzee have 

a parallel-sided palates

.



While the 

palates of the 

Australopithecus

have a

U-shaped palate

.

5.

Cranial ridges:



Cranial ridges 

are found 

at the back 

of the 

skull

.



Cranial ridges of humans do not protrude 

as

those of 

ape men

.

6.

Brow ridges:



The 

ape men have larger brow ridges 

than

humans.



In most cases the 

brow ridges in humans are

absent

.

3.2.1

A – Gorilla

B – Modern human

3.2.2

3.2.3 

B

3.2.4  

Allows total awareness of the environment in

sensing

danger/looking for food

- Enables hands to be free to use  implements

/carry 

objects or offspring/throw/protect

- Exposes a large surface area for thermo-

regulation /lose body heat to surroundings in hot

conditions/reduce overheating therefore reduce

need for water

- Display of male/female sex organs as part of

courtship behaviour



You can use these answers to enhance or

even make your studying easier.



You can use the table to learn the

differences between the African Apes

and modern human.



The answer to question 3.2.4 can be used

to learn the advantages of bipedalism

3.1.1

(a) 

Pan troglodytes/chimpanzee/C

(b) 

Homo erectus/A

(c) 

Homo sapiens /B

OR

(a) 

Homo erectus/A

(b) 

Pan troglodytes/chimpanzee/C

(c) 

Homo sapiens /B (3)

Remember

: 

that if scientific names are

not underlined you will lose the marks!!!!

3.1.2

Learn this table too

The following essay appeared in the Nov 2013 paper

1.

4.3 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 .

4.3

Foramen magnum

- The foramen magnum was in a backward position in the ape-like

beings

- but in a forward/ central/ ventral position in modern humans

Significance

- This represents a change from quadrupedalism in ape-like beings

- To bipedalism/(walking upright) in modern humans, leading to the

following in modern humans:

o Increased awareness of the environment

in sensing danger/food

o Freeing of the hands to use implements/ carry objects/ weapons/

offspring

o Exposure of a large surface area for thermoregulation/losing body



Display of sex organs /breasts as part of courtship

behaviour

Cranium

- Modern humans have a larger cranium

than the

ape-like beings

-

Modern humans have a less sloping forehead

than

the ape-like beings

-

Modern humans have a cranium that is more

rounded

than the ape-like beings

Significance

- This allowed space for a larger brain

in humans

than in ape-like beings, making the following

possible:

o Better co-ordination of movement

o Processing of a large amount of information

o Processing information faster

o Development of spoken and written languages to

communicate



Jaws

- 

Humans have smaller jaws

than the ape-like

beings

-

Humans have jaws that are non-prognathous/ flat

face

-

compared to the jaws of ape-like beings which are

prognathous/sloping face

-

Humans have C-shaped jaws

/jaws that are gently

curved

-

compared to the U shaped jaws

in the ape-like

beings

Significance

-

This corresponds with a change in diet from hard, raw

food

in the ape- like beings

-

To softer, cooked foods

in humans

Dentition/Teeth

- In ape-like beings there are gaps/diastema between

incisors and canines

- but no gaps

between the teeth in humans

- Humans have smaller teeth/incisors and canines 

than

the ape-like beings

- Humans have flatter molars and pre-molars

than the

ape-like beings

Significance

- This corresponds with the decreased need to bite and tear

-

and an increased need to grind and chew

in humans  in

view of the change in diet to soft, cooked food

Eyebrow ridges

- Humans have eyebrow ridges that are smaller

than those of

the ape-like beings



Significance

- There is a decreased need to strengthen the skull

of humans

- due to the smaller size of the jaws

-

Chin

- In humans the chin is more developed

compared 

to the ape-like

beings

Significance

- Developed chin assists with speech 

in humans

Zygomatic arch

- In humans the zygomatic arch/cheek bone is less developed

than

in the ape-like beings

Significance

- This corresponds with the decreased need for attachment of

strong muscles

-

due to the decreased jaw size

in humans



Hominid

: refers to the group including modern

humans, chimpanzees, gorillas and orangutans.



Hominin

: refers to modern humans and all the

extinct human species



Transitional fossils

: refers to the immediate

fossils between a group and their ancestor



Arboreal

:  

refers to living in trees



Stereoscopic vision

:  

refers to see the depth and

solidity of objects



Binocular vision

:  

the process of looking at an

object with both eyes



Opposable thumb

:  

the thumb is opposite the

fingers



Bipedalism

:  

refers to a type of locomotion where

the animal moves on 2 hind legs in an upright

position



Dentition

:  

refers to the development of teeth and

the way they are arranged in the mouth



Prognathous

:  

refers to the projection of the jaws

and nose that leads to a pointed face.

1.

Characteristic/s that humans share with other

primates…

A.  Opposable thumbs

B.  Binocular vision

C.  Both A and B

D.  Neither A nor B

2.

Homo habilis

…

A.  was called Handyman because he was a

toolmaker.

B.  had a larger  brain capacity than 

Homo

erectus

.

C.  was the first Homo species without brow

ridges.

D.  was the first Homo species to leave Africa.

3.

An opening on the primate skulls through which

the spinal cord passes…

A.  Foramen magnum

B.  Vertebral column

C.  Spine

D.  Vertebrae

4.

Capable of bipedal locomotion…

A.  

Homo erectus

B.  

Australopithecus africanus

C.  Both A and B

D.  Neither A nor B

5.

A branched diagram showing the evolutionary

relationships between species…

A.  Cladogram

B.  Phylogenetic tree

C.  Both A and B

D.  Neither A nor B

6.

The group consisting of modern humans,

chimpanzee, gorillas and orangutans and all

their ancestors is…

A.  Hominid

B.  Hominin

C.  Both A and B

D.  Neither A nor B

7.

Australopithecus, Panantropus 

and 

Ardipithecus

belong to…

A.  Hominid

B.  Hominin

C.  Both A and B

D.  Neither A nor B

8.

Walking on 2 legs…

A. Bipedalism

B.  Quadurpedalism

C.  Both A and B

D.  Neither A nor B

9.

A fossil that is intermediate between a group

and their ancestor…

A.  Middle fossil

B.  Mean fossil

C.  Transitional fossil

D.  None of the above

10.

Having a long face that sticks forward…

A.  Prognathous

B.  Non-prognathous

C.  Diastema

D.  Flatter face

11.

Chimpanzee…

A.  Prognathous

B.  Non-prognathous

C.  Both A and B

D.  Neither A nor B

12.

Humans…

A.  Prognathous

B.  Non-prognathous

C.  Both A and B

D.  Neither A nor B

13.

Structure or parts of the body…

A.  Ancestor

B.  Anatomy

C.  Both A and B

D.  Neither A nor B

14.

U-shaped jaw…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

15.

Prominent brow ridges…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

16.

Absence of cranial ridges…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

17.

Binocular vision…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

18.

Altricial development…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

19.

Forward foramen magnum…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

20.

Spatula shaped incisors…

A.  Humans

B.  

Australopithecus

C.  Both A and B

D.  Neither A nor B

1.

C

2.

A

3.

A

4.

C

5.

C

6.

A

7.

B

8.

A

9.

C

10.

A

11.

A

12.

B

13.

B

14.

B

15.

B

16.

A

17.

C

18.

C

19.

C

20.

D