Human evolution skeletal changes Flashcards
Skull in a quadruped (foramen magnum)
the foramen magnum lies towards the rear of the skull so the large neck muscles are needed to prevent head from sagging forwards.
(An opening close to the rear of the skull implies a quadrupedal habit of locomotion the head is held upright by powerful neck muscles.)
Skull in humans
the foramen magnum lies in the centre directly under the skull. Enabling the skull to be balanced on the spine rather than hanging from it.
Little muscular energy is needed to support the skull, and this helps overcome the gravity when walking upright.
- An opening located more centrally on the skull implies a bipedal habitat of locomotion: the head balances on the spine and less power of neck muscles
Spine in biped
is “s” shaped, and flexible which allows shock absorption while walking. It keeps weight of the upper body to be carried nearly directly above the hip (centre of gravity) for efficient walking.
spine in quadruped
the spine has a single curve (straight/ “c” shape) counterbalances the force of all of their organs pushing downward due to gravity when walking on all fours.
power grip in humans
enabled human to wrap the thumb and fingers on an object
precision grip in humans
enabled humans to hold and pick objects steadily using their fingers.
precision grip note: fingers directly opposing thumb allows precision grip and thus …..
able to create tools with precision
Hands in quadruped (brachiating, power grip)
-Curved fingers for brachiating (swinging)
-Power Grip: fingers and thumb wrap around the object
- less motor skills
(short thumb, curved phalanges, power grip, no saddle joint, less sensitive fingertips, clumsier motor control, long fingers)
Hands in biped
-straight fingers
-precision grip : thumb & finger grip objects more fine motor skills
-better able to use tools, acquire food
-opposable thumb
Compare and contrast points of biped and quadruped (hands)
- fingers
- thumb
- size, mobility, sensitivity
Humans have straight fingers, whereas primates have curved fingers
Thumb of humans is proportionally longer than other primates. This allows humans to have both power and finger grip.
Human - longer + mobile thumb give us precision grip. + sensitive finger pads enables us to manipulate objects better than apes.
Pelvis in apes
the pelvis is long and narrow. Because their femur joint is vertical
Pelvis in humans
Have a shorter and broader pelvis.
what is the purpose of a human having a shorter and boarder pelvis
The shorter and boarder pelvis (forming a bowl shape) supports the abdominal organs when standing upright.
Also it allows the attachment of the gluteus maximus muscles, for walking.
the position of the gluteus maximus helps the hamstrings to pull the leg back whereas it does not have, this function in quadruped.
The reduced height brings the sacro-iliac joint closer to the hip joint reducing stress on the ilium that transmits the entire weight of the upper body from the spine to the pelvis
[FEMUR SHAPE AND LENGTH]
IN A BIPED
The femur is longer angled inwards from the hips, so that the knees almost touch. This allows the knee and the food to be directly under the centre of gravity, allowing greater stability when walking in an upright stance.
[KNEE JOINT]
IN HUMAN
The bottom of the femur (knee joint) has a buttress of bone (lateral condyle) that stops the sideways deflection of the lower leg during walking.
[FOOT]
IN HUMANS
the foot is arched. The weight is placed on the outer edge of the foot with the inner side elevated into arch providing a shock absorbing effect and spring for long distance walking.
Human toe (non opposable)
The non opposable big toe that is aligned with other toes allows the balance and thrust when moving forward. The heel provides balance and support.
opposable big toe apes
crucial for aboreal lifestyle to grasp and climb onto branches
Apes cranium size
smaller cranial capacity (450 cc)
H. sapiens cranial capacity
bigger cranial capacity (1450cc)
why did the cranial capacity increase from apes to humans
brain development
Describe (brief) for apes
- sagittal crest?
- zygomatic arch
- jaw
- teeth size
- brow ridge?
-Sagittal crest
-Large zygomatic arch
-Large jaw
-Teeth Bigger
-Brow ridge
Describe (brief) for homo sapiens:
-sagittal crest?
-zygomatic arch
- Jaw
-Smaller
-brow ridge??
- no sagittal crest
-Small zygomatic arch
-Small Jaw
-Teeth Smaller
-No brow ridge
Is there a nuchal crest in apes
yes
is there a nuchal crest in humans
no
why did the nuchal crest disappear from humans to apes
Head vertical on spine - less muscle attachment needed
in apes the foramen magnum is located….of the skull
at the rear
in humans the foramen magnum is located….. of the skull
at the centre
Does the apes have a brocas and Wernickes area.
no
do humans have a brocas and Wernicke’s area?
yes
what is the purpose of the brocas and wernicke’s area
used for language.
what’s the difference between the folding of the cortex of humans and apes.
Less folding of the cerebral cortex in apes, and more folding of the cerebral cortex in humans
why is the cerebral cortex more folded in humans than in apes?
Related to memory attention language awareness and thought etc.. developed as social structure allows more time and hands free to carry out abstract tasks
Cerebellum is …. developed in apes
less
Cerebellum is …. developed in humans
more
what is the purpose of the cerebellum
Needed for balance as well as coordination and tool use
