AN UNUSUAL APE W.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.

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.

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.