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Hominins
This is the Hominid sub group made up of human and their human like ancestors
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Several other hominin forms are now
extinct such as Homo Habilis and Australopithecus
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This means they they
are not only capable of walking on two legs, but that it is their habit to do so
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The features of Hominins ultimately relate to their bipedal lifestyle
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Describe trends of biological evolution with respect to skeletal changes linked to
bipedalism
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Humans have taken this to the extreme and walk on two
legs all of the time
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It is
thought that being bipedal allowed humans to exploit the ground niches, which probably
offered more variety of food at a time when forests were shrinking
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This change to bipedalism was
probably the most important step in our evolution because it freed the hands, allowing us to
take advantage of our larger brain
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● The human pelvis is relatively short and strong in a bowl shape in order to carry the
weight of an upright body whereas Apes have a longer narrower pelvis
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This brings the knees and feet nearer the midline, which enables more efficient two
legged walking compared to chimpanzees
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In apes the knees bend outwards under the hips as their
femur angled into the knee so when they lift one foot off the ground they lose
balance
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This produces a swaying
movement as they walk
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This is so that the eyes can face forwards when standing
upright
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Their feet are
also flat
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● Human​ hands​ are much smaller than a chimpanzee’s, the thumb is relatively long
and more mobile
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A
chimpanzee's hand is not suited to a precision grip but human hands can have both a
power grip and a precision grip
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Like all primates both can grip
objects with a ​power grip​, but only humans can also use a ​precision grip​
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Apes had a ​flatter brain case​ (smaller brain) which allows for greater muscle attachment
sites needed for aggressive facial displays
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It is very likely that large
teeth and large jaws are associated with diets high in fibrous plant food
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These stresses are resisted by the ​brow ridges above the eye sockets and
the ‘siminian shelf’​ that strengthens the inside of the lower jaw
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● Canine teeth ​in males and females are the same size in humans but in apes they are
much larger in males
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​ Not the case in humans
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● Hair loss helped as our ancestors lived in tropical Africa and lived and worked
outside, so it helped to evaporate sweat and keep cool by having thin hair
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● Apes had a shorter ​Pharynx tract​ this was one of the reasons they cannot have
spoken language
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● Increase in brain size is mainly due to the increase in
size of the ​cerebrum​
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● Wernicke’s area ​is a sensory region concerning the
interpretation of sound
● Broca’s area ​is a motor region, responsible for the interpretation of sound into
meaningful sequences
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● Cranial capacity changed from about 400cc to 1500cc
Apes have a much smaller brain size 450cm​3 ​vs 1400cm​3
Chimpanzee’s have a brain size of 400cm​3

Apes (quadrupedal)

H
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Pelvis is long and narrow

Pelvis short and
wide

Supports organs above​, also must allow
for bigger head during birth
Changed ​shape of the hominin pelvis
beneficial in locomotion:
Changes ​position of muscle attachmen​t
more efficient locomotion;
Carrying angle​ – more efficient
locomotion because movement
notside to side (or implied) /
balance /stability when walking
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Position of the occipital condyles (the part of
the skull that articulates with the vertebral
column)

They have moved from the back of the skull to the
middle of the skull to keep to keep the head above
the centre of gravity

Rib cage

Flattened ​from front to back ​which moves the
centre of gravity closer to the spine
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Spine shape

Changed from ‘C’ shape to ‘S’ shaped
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This improves both balance and
it absorbs the shock of walking
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This results in:(a)​ ​Improved balance
(b)​ ​The support of the upper body
(c)​ ​Enlarges the valgus angle
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Femur length and shape

Femur is stronger, ​longer​ and angled inwards from
the hip so that the knees nearly touch (increased
valgus angle)
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Overall the legs are longer than the arms in humans
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Shape of the foot

The foot has changed in two main ways:(a)​ ​The foot has changed to become a platform
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The foot has lost all grasping
ability
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This provides
a shock absorber effect and a spring that
facilitates long distance travelling
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You should be able to see that the
top of the femur increases in size, which reflects the increased weight load on the joint as
humans spent more time walking on two legs and grew larger in size
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In humans however, the thumb is enlarged
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Humans are the only ape which can achieve the full thumb tip to
finger tip ​precision grip​
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Lastly, the
bones of the fingertip have an enlarged apical tuft, which increase the surface of the finger
tip for grasping fine objects
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sapiens

Reason for change

Smaller cranial
capacity (~450cc)

Bigger cranium
(~1450cc)

Increased brain development

Sagittal crest
Large zygomatic
arch
Large jaw
Teeth bigger
Brow ridge

No Sagittal crest
Small zygomatic arch
Small jaw
Teeth smaller
No brow ridge

More refined diet, no need for really
strong chewing muscles, muscle
attachment points, or teeth

Nuchal crest

No Nuchal crest

Head vertical on spine – less
muscle attachment needed

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