Evolutionary Trends in Hominids

Question 1

List the three forms of groups in classifying humans.

Answer 1

1. Family.
2. Subfamily.
3. Tribe.

Question 2

What does the ‘family’ group include in classifying humans?

Answer 2

• The Hominidae/Hominids.
• The Great Apes and Humans.

Question 3

What does the ‘subfamily’ group include in classifying humans?

Answer 3

• The Homininae/Hominines.
• The Humans, chimpanzees and gorillas, separated from orangutans.

Question 4

What does the ‘tribe’ group include in classifying humans?

Answer 4

• The Hominini/Hominins.
• The Humans and extinct ancestors separated from chimps and gorillas.

Question 5

List the 8 adaptations for erect posture and bipedalism in humans.

Answer 5

1. Position of the foramen magnum.
2. Curvature of the spinal column.
3. The jaw.
4. The pelvis.
5. The carrying angle.
6. The knee.
7. The foot.
8. The centre of gravity.

Question 6

What is the foramen magnum?

Answer 6

The opening beneath the cranium through which the spinal cord passes.

Question 7

Describe the position of the foramen magnum as an evolutionary trend.

Answer 7

• The foramen magnum has gradually moved forward to become more central.
• This means the skull can be balanced on top of the spine and large neck muscles are not required.
• The foremen’s magnum is found towards the back in Gorillas so they need large neck muscles to hold their head in place.

Question 8

Describe the curvature of the spinal cord as an evolutionary trend.

Answer 8

The smooth C-shaped curve in the spines of apes has evolved into an S-shaped curve in humans. The double curvature in the lumbar vertebrae is wedge-shaped from front to back. The curvature of the cervical vertebrae aligns with the vertebral column directly under the centre of the skull. This has improved balance and allows the head to be balanced on top of the neck.

Question 9

Describe the pelvis as an evolutionary trend.

Answer 9

The pelvis in humans is broader and shorter than apes and is bowl-shaped. Broad hip bones allow for the attachment of muscles to move legs and keep erect position.

Question 10

Why is the female pelvis slightly broader than males?

Answer 10

To allow the passage of an infant during childbirth.

Question 11

List the 3 points a bowl-shaped pelvis supports.

Answer 11

1. The abdominal organs.
2. Provides greater stability for bipedal locomotion.
3. Supports a developing foetus in women.

Question 12

What is the carrying angle?

Answer 12

The arrangement of the thigh bones to form an angle to the vertical.

Question 13

What is the femur?

Answer 13

The thigh bone.

Question 14

What is the acetabulum?

Answer 14

The socket of the pelvis in which the head of the femur fits.

Question 15

Describe the carrying angle as an evolutionary trend.

Answer 15

• The pelvis shape allows for the hip joint to be directly under the trunk and head.
• The large head fits into the acetabulum. A wide pelvis allows the femur to converge towards the knee. The femur angled towards the knee forms the carrying angle.
• Weight distribution remains close to the central axis. The carrying angle allows for good stability when walking.

Question 16

List the 3 points on how the carrying angle results in greater stability.

Answer 16

1. The body can rotate about the lower leg.
2. Each footstep follows a straight line.
3. Creates the striding gait.

Question 17

Describe the knee as an evolutionary trend.

Answer 17

• In a bipedal species, the weight of the body is distributed down the outside of the knee. The outer ligament is larger and stronger.
• Although the weight of the body is transmitted down the side of the leg, the centre of gravity falls in front of the knee. L
• igaments create a resistance to the knee bending backwards.
• The natural resistance produces a joint that requires no energy to support the body in a standing position.

Question 18

What are the metatarsals?

Answer 18

The bones of the foot are between the toes and ankle.

Question 19

List the 2 types of arches found in the Human foot.

Answer 19

1. Longitudinal arch.
2. Transverse arch.

Question 20

What is the longitudinal arch?

Answer 20

The arch of the bones of the foot, running from front to back.

Question 21

What is the transverse arch?

Answer 21

The arch of the bones of the foot, running from side to side.

Question 21

Describe the foot as an evolutionary trend.

Answer 21

Weight is transferred from the knee to the tibia to the ankle. It has lost its prehensility. This is most noticeable with the big toe, which in humans is large and algins alongside the other toes. Metatarsals are shaped to form longitudinal and transverse arches.

Question 22

What is the centre of gravity?

Answer 22

Is the point at which the weight of the body is concentrated.

Question 23

Describe the centre of gravity as an evolutionary trend.

Answer 23

Humans have legs longer than arms which increase the length of stride and lowers the centre of gravity. A lower centre of gravity creates stability during bipedal locomotion and standing erect.

Question 24

What is muscle tone?

Answer 24

The partial contraction of skeletal muscles.

Question 25

Describe muscle tone as an evolutionary trend.

Answer 25

Muscle tone supports upright positions in the hip, knee, ankle, abdominal and spine. For example, to keep the head erect and stop it from slumping forward muscles in the neck are partially contracted.

Question 26

What is the striding gait?

Answer 26

Is the full extension of the hip and knee into a straight position while walking.

Question 27

Outline the 4 steps of the striding gait in motion.

Answer 27

1. Foot hits the ground. 2. Weight is transmitted from the heel along the outside of the foot. 3. Weight crosses the ball of the foot. 4. Then to the big toe.

Question 28

Describe the striding gait as an evolutionary trend.

Answer 28

Homins are the only animals to perfect this locomotion. The foot has evolved to be weight-bearing. The trunk rotates about the pelvis. Forward-swinging arms compensate for movement. The right arm swings forward as the left leg extends. The swinging of arms keeps shoulders at the right angles.

Question 29

What is the average size of the human brain?

Answer 29

1350cm^3.

Question 30

What is the average size of an Ape brain?

Answer 30

400 to 500cm^3.

Question 31

What percentage of the human brain is dedicated to the frontal lobe?

Answer 31

47%.

Question 32

What percentage of the ape brain is dedicated to the frontal lobe?

Answer 32

33%.

Question 33

Describe the size of the cerebral cortex as an evolutionary trend.

Answer 33

The difference in size between humans and apes is associated with the cerebrum. There has been an increase in cranium capacity, as more of the skull is used to house the brain. This means humans lack prominent brow ridges.

Question 34

Describe prognathism and dentition as an evolutionary trend.

Answer 34

A forward jutting jae has decreased to a flat face. There has been a gradual decline in tooth size and a decrease in the brow ridge size. The dental arcade has changed from U-shaped to parabolic-shaped.

Question 35

What is brachiation?

Answer 35

Arboreal locomotion in which movement is accomplished by swinging from one hold to another by arms.

Question 36

What does arboreal locomotion refer to?

Answer 36

Tree living organisms.

Question 37

List 4 adaptations for brachiation.

Answer 37

1. Longer arms than legs. 2. Flexible shoulder joints. 3. Long and strong fingers for grasping. 4. Some primates have shorter thumbs.

Question 38

List 6 advantages of bipedalism.

Answer 38

1. More energy efficient. 2. Leaves the hands free to use tools. 3. Leaves the hands free to carry items. 4. An upright stance achieves greater height and thus the ability to see further. 5. An upright stance means that less of the body is exposed to sunlight. 6. Upright stance increases exposure to breezes, increasing cooling mechanisms.