Evidence for the Evolutionary Relationship

Biochemical/Genetic Evidence An evolutionary tree can be drawn up from the slight differences in the composition of different proteins in the present-day hominoids. From this it has been determined that humans and chimpanzees are closely related, and did not break away from a common ancestor until quite recently.

Behavioural Evidence The apes form social groups with mutual grooming and quite complicated heirarchy arrangements. We can see echoes of our own behaviour.

Human Behaviour This is characterised by some of the following abilities: Behave co-operatively. Suppress or channel rage and aggression. Sustain motivation or drive for long periods of time. Form close affectionate ties with adults of the opposite sex. Make and use tools. Comminicate with speech.

Differences Between Humans and Apes Many of the body changes to allow upright bipedal walking relate to shifting the centre of gravity of the body.

The Skull This consists of a rounded brain case surrounding and protecting the enlarged brain. It provides attachment for muscles. It is balanced on the vertebral column. The part of the skull that articulates with the vertebral column is called the Occipital Condyles. In humans this is relatively far forward.

The Skull In humans, the Foramen magnum (the hole that the spinal cord passes to the brain), is positioned underneath the skull. In quadrapeds it faces towards the back. In humans the are for the attachment of the neck muscles is small and directed downwards. Apes have large faces with heavy jaws and large neck muscles attached to a large area at the back of the skull, which has a prominent ridge called the Nuchal crest.

Gorilla and Human Foramen Magnum

The Skull Jutting out from the top of the ape’s head is a bony ridge, the saggital crest for the attachment of the heavy chewing muscles. Humans have large brains (1400cm3 apes – 400-500cm3). In humans the face is relatively flat, and the forehead rises from the eyes. In apes the forehead slopes back from the eyes and there is a bulge across the top of the eyes called brow ridges.

The Skull Apes have the lower face and jaw projecting in front of the upper parts of the face. Are Prognathic. Some early humans have wide flaring cheekbones called zygomatic arches prominent in Paranthopus robustus. Modern humans have a chin and a nose which sticks out. Apes have no chin and a flat nose.

The Teeth and Jaw Human teeth are unique. Both males and females have small incisors and canines that do not project further than the other teeth. In apes both are larger and are used mainly for asserting dominance and in aggressive displays. Apes have a diastema (gap) in the lower jaw in which the canines fit. These canines shear against the first premolars.

The Teeth and Jaw The first premolar has only 1 cusp; the second has 2. In humans both premolars have 2 cusps. In humans the roof of the mouth or Palate is arched and the row of teeth is shaped like a rounded ‘V’. In apes the palate is flat, and the teeth row is shaped like a ‘U’ with parallel sides.

The Pelvis and Backbone In Humans the backbone is ‘S’ shaped. In apes, the spine is arched. The pelvis in humans is broad, shallow from top to bottom and bowl-shaped. Apes have narrow, elongated pelvic bones. In humans the centre of gravity is just behind the lower back above the legs, giving better balance in an upright stance.

The Pelvis and Backbone In humans the large gluteus maximus muscles support the femur and pelvis in an upright position. Apes have much smaller gluteus maximus muscles and support their body with their arms on the ground.

The Legs In humans the heads of the femurs are far apart, while the knee ends are close together. This forms an angle to the vertical, the valgus angle. This helps to shift body weight closer to the centre of gravity.

The Legs Where the femur meets the knee are 2 bone projections called the Condyles. In humans, because the weight is shifted to the outside of the femur, the outer condyle is larger than the inner one. In apes the opposite is true. In humans the legs are longer than the arms. In apes the arms are longer than the legs.

The Feet In humans the toes are short. The big toe is longer and lies close and alongside the other toes. In apes there is a gap between the big toe and the rest. In humans the weight is taken on the outside of the foot, the inner side is arched. Apes have flat feet.

The Chest Humans have broad, narrow chests which are flattened from front to back. In apes the the chest is flattened at the sides. Humans have longer clavicles. In humans the shoulder blades lie on the back rather than along the sides of the chest as in quadrapeds.

Other The human thumb is longer and more mobile than the apes’. The sensitive pads of the thumb can be opposed to the sensitive pads of the other fingers, which allow fine manipulative work. In apes the thumb is short and the fingers are long, so there is no precision grip.

Other In humans the mobile hand is controlled by an improved brain. Humans are relatively hairless, although we have as many hair follicles as the apes.

Bipedalism: The Good and The Bad…… ADVANTAGES DISADVANTAGES See further Back-arches Frees hands, can throw stones and wield sticks Painful birth Can carry babies Takes a long time to learn to walk Can keep cooler Varicose veins Look larger and more menacing More visible to predators Greater display of sexual organs