Evidence of a Common Ancestor for Living Hominids & Differences

Question 1

Why is it important to show that hominids have a common ancestor?

Answer 1

• if there is a common ancestor we will be able to trace the evolution of humans from this ancestor
• through the series of early hominin species to today’s humans

Question 2

When did the common ancestor of African apes and humans exist?

Answer 2

• about 6 million years ago

Question 3

What are the anatomical similarities of all living hominins?

Answer 3

• upright posture
• lack external tails
• freely rotating arms
• hands with an opposable thumb
• digits with flat nails, instead of claws or hooves
• eyes that face forward
• molar and premolar teeth with low and rounded cusps
• eyes with cones for colour vision
• sexually dimorphic
• large brain compared to body mass

Question 4

Why do hominins have eyes that face forward?

Answer 4

• so that the eyes’ visual fields overlap to five stereoscopic vision

Question 5

Why do hominins have flat nails?

Answer 5

• probably to allow for manipulation that is more sensitive

Question 6

What does it mean to be sexually dimorphic?

Answer 6

• this means that males and females vary in some physical trait
• e.g. males are about 5 to 10% larger and have an upper body with larger muscles

Question 7

What are the anatomical differences between humans and African apes largely related to?

Answer 7

• the evolution of habitual bipedalism in humans

Question 8

What is bipedalism?

Answer 8

• the ability to walk upright on 2 legs

Question 9

What are the differences between humans and apes in terms of limb structure?

Answer 9

Apes:
- arms that are usually longer than the legs
Humans:
- arms that are shorter and weaker than the legs (long arms were no longer needed for climbing)

Question 10

What are the differences between humans and apes in terms of digits?

Answer 10

Apes:
- fingers and toes that are long and curved for grasping branches
- big toes that are divergent
Humans:
- fingers and toes that are short and straight
- thumbs that can grasp objects precisely and firmly between the tops of the fingers and thumb

Question 11

What characteristics do apes have in terms of their hipbones and why?

Answer 11

• ilia (hipbones) that are large, elongated and parallel to the spinal column
• this is to support the legs and trunk in the bent-over posture necessary for quadrupedal knuckle-walking

Question 12

What are the differences between humans and apes in terms of spines?

Answer 12

Apes:
- a bow-shaped, less curved spine
Humans:
- a spine curvature that has two major curves, the thoracic and the lumbar

Question 13

Why do humans have S-shaped spines?

Answer 13

• to keep the trunk of the body, and the weight of it, centred above the pelvis
• which is crucial for efficient upright walking

Question 14

What characteristics do humans have in terms of their pelvis and why?

Answer 14

• a shorter, broader and more bowl-shaped pelvis
• which supports the legs and trunk in an upright position
• thus providing greater stability for walking and running

Question 15

What characteristics do humans have in terms of their femurs and why?

Answer 15

• longer femurs that are set farther apart at the hips than they are at the knees and slant toward the midline
• to keep the knees close together
• making walking and running more efficient

Question 16

What characteristics do humans have in terms of their feet and why?

Answer 16

• a large strong heel
• tiny toes with the large big toe moved into line with the other (convergent)
• longer feet with a stable arch, which supports the body better
• adapted to support the whole weight of the body and for walking or running

Question 17

What is the main difference between the brains of humans and apes?

Answer 17

• humans have a much larger brain
• especially the cerebral cortex

Question 18

What is the larger more complex brain of the human responsible for?

Answer 18

• the unique behavioural qualities of humans

Question 19

What do the unique behavioural qualities of humans include?

Answer 19

• using their hands with greater dexterity to make simple tools
• the use and control of fire
• the use of a highly developed language

Question 20

What is the difference between the skull of an ape and a human in terms of the brow ridge?

Answer 20

• humans do not have the pronounced brow ridges of an African ape

Question 21

What is the difference between the skull of an ape and a human in terms of the foramen magnum?

Answer 21

Apes:
- foramen magnum is at the rear of the skull
Humans:
- foramen magnum is found centrally under the skull

Question 22

Why is the foramen magnum situated under the skull in humans?

Answer 22

• so that the head is held firmly upright
• the body’s centre of gravity is directly over the legs
• reducing the energy needed to balance

Question 23

Why is the foramen magnum situated at the rear of the skull in apes?

Answer 23

• to allow for the attachment of strong neck muscles
• and to place the head at an angle
• the proper position for walking on all fours

Question 24

What is the difference between the skull of an ape and a human in terms of structure?

Answer 24

Apes:
- small braincase
- large jaws
- a sloping face
- no chin
Humans:
- large braincase
- small jaws
- nearly vertical face
- a chin

Question 25

What do the structural differences between the skull of an ape and a human suggest?

Answer 25

• that the cranial capacity of the African ape is smaller than that of humans
• that their diet is different

Question 26

What is the difference between the skull of an ape and a human in terms of teeth?

Answer 26

Apes:
- large
- pointed
- project beyond the other teeth
Humans:
- relatively small