AN UNUSUAL APEW.A.L.T- Describe trends in human evolution by discussing skeletal

changes linked to bipedalism.

BIPEDALISM

• Humans – only primates to stand on two legs easily for long periods.

BIPEDALISM

• Humans – only primates stand on two legs easily for long periods.

• This depends on a number of features in our muscular and skeletal systems.

SKULL

• Foramen magnum – the hole in the skull where the spinal cord leaves.

SKULL

• Foramen magnum – the hole in the skull where the spinal cord leaves.

• In an ape, the FM is at the rear – large neck muscles are needed to prevent the head from sagging.

SKULL

• Foramen magnum – the hole in the skull where the spinal cord leaves.

• In an ape, the FM is at the rear – large neck muscles are needed to prevent the head from sagging.

• In humans, the FM is in the centre – skull is balanced on the first neck vertebra = little muscular energy required.

SKULL

• Foramen magnum – the hole in the skull where the spinal cord leaves.

• In an ape, the FM is at the rear – large neck muscles are needed to prevent the head from sagging.

• In humans, the FM is in the centre – skull is balanced on the first neck vertebra = little muscular energy required.

• https://www.youtube.com/watch?v=xT8Np0gI1dI

VERTEBRAL COLUMN (BACKBONE)

• Ape – single curve

VERTEBRAL COLUMN (BACKBONE)

• Ape – single curve

• Human – 3 curves, giving an ‘S’ shape. This helps to keep the chest more directly above the hips = body weight is concentrated in a near-vertical line above the feet.

HIP GIRDLE

• In Quadrupedal mammals (4 footed) the hip bone is long.

HIP GIRDLE

• In Quadrupedal mammals (4 footed) the hip bone is long.

• Humans – hip bone forms a bowl-shape. This supports the abdominal organs.

HIP GIRDLE

• In Quadrupedal mammals (4 footed) the hip bone is long.

• Humans – hip bone forms a bowl-shape. This supports the abdominal organs. The reduced height of the pelvis brings the sacro-iliac joint closer to the hip joint.

Hip joint

HIP GIRDLE

• In Quadrupedal mammals (4 footed) the hip bone is long.

• Humans – hip bone forms a bowl-shape. This supports the abdominal organs. The reduced height of the pelvis brings the sacro-iliac joint closer to the hip joint. This reduces the stress on the ilium – transmitting the entire weight of the upper body from the backbone to the hip joint.

FEMUR & KNEE

• Humans – ‘knock-kneed’ = knees almost directly under the centre of the hip girdle.

FEMUR & KNEE

• Humans – ‘knock-kneed’ = knees almost directly under the centre of the hip girdle.

• Valgus angle – between the femur and the mid-point of the hip girdle.

FEMUR & KNEE

• Humans – ‘knock-kneed’ = knees almost directly under the centre of the hip girdle.

• Valgus angle – between the femur and the mid-point of the hip girdle.

• Results in – humans don’t sway when walking, apes do.

• https://www.youtube.com/watch?v=fJSYQ9l-Xdw

• https://www.youtube.com/watch?v=HBUKRFXGuqo

FOOT

• The human foot differs from that of the great apes.

1. The foot is arched and ligaments on the underside prevent sagging. These act like springs when stretched (foot on ground) therefore releasing energy to push the foot upwards.

FOOT

• The human foot differs from that of the great apes.

1. The foot is arched and ligaments on the underside prevent sagging. These act like springs when stretched (foot on ground) therefore releasing energy to push the foot upwards.

2. The big toe is enlarged and points forward (in apes it goes out to the side) = final thrust against the ground. We can’t grip branches anymore though

FOOT

• The human foot differs from that of the great apes.

1. The foot is arched and ligaments on the underside prevent sagging. These act like springs when stretched (foot on ground) therefore releasing energy to push the foot upwards.

2. The big toe is enlarged and points forward (in apes it goes out to the side) = final thrust against the ground. We can’t grip branches anymore though

3. Toes are straight in side view compared with apes which are curved.

SOME PROBLEMS

• Inner-vertebral discs can become damaged – lower back pain.

SOME PROBLEMS

• Inner-vertebral discs can become damaged – lower back pain.

• The foot arch may be flat = not able to walk as far comfortably.

SOME PROBLEMS

• Inner-vertebral discs can become damaged – lower back pain.

• The foot arch may be flat = not able to walk as far comfortably.

• Bipedal posture can make it harder for blood to be returned to the heart from the legs if too sedentary = varicose veins.

HANDS

• Hands are essential for manipulating objects.

HANDS

• Hands are essential for manipulating objects.

• The thumb is longer, and is able to touch the tip of any other finger (opposable).

HANDS

• Hands are essential for manipulating objects.

• The thumb is longer, and is able to touch the tip of any other finger (opposable).

• All primates can use the ‘power grip’ but only humans are capable of the ‘precision grip’ as well.

TEETH AND JAWS

• Much smaller in humans than apes – linked because with the development of tools = less important.

TEETH AND JAWS

• Much smaller in humans than apes – linked because with the development of tools = less important.

• In apes, the lower canine fits into a diastema (gap) between upper canine and first pre-molar. Humans have no diastema.

BRAIN

• The largest expansion of the human brain was in the cerebrum.

BRAIN

• The largest expansion of the human brain was in the cerebrum.

• Our brains are extensively folded to increase surface area.

BRAIN

• The largest expansion of the human brain was in the cerebrum.

• Our brains are extensively folded to increase surface area.

• This area is reasoning, maths abilities, language, abstract thought and imagination (as well as sensory perceptions).

SPEECH

• Development of speech – one of the most significant advances in human evol.

SPEECH

• Development of speech – one of the most significant advances in human evol.

• Involves structure of the pharynyx but also the organisation of the brain.

SPEECH

• Development of speech – one of the most significant advances in human evol.

• Involves structure of the pharynyx but also the organisation of the brain.

• Sounds words complex sequences sentences. As well as listening and understanding.

SPEECH

• Development of speech – one of the most significant advances in human evol.

• Involves structure of the pharynyx but also the organisation of the brain.

• Sounds words complex sequences sentences. As well as listening and understanding.

• Broca’s area – organisation of sounds into meaningful sentences.

• Wernicke’s area – interpretation of sounds that are heard.