chapter 12 Flashcards
Family Hominidae: chimps, bonobos, gorilla, orangutans, humans – members are hominids
chimps, bonobos, gorilla, orangutans, humans – members are hominids
great apes
7 characteristics
Larger, more complex brain than other primates.
Enables ↑ cognitive ability –
5 cusps in the molar teeth of the lower jaw
Arms that can freely rotate at the shoulder
A wide, shallow chest cavity
NO external tail
An appendix
Diurnal – active during the day
Variations to Family Hominidae Characteristics
Relative size of cerebral cortex
Mobility of the digits
Locomotion – adaptations to bipedalism (2 legs) and quadrupedalism (4 limbs)
Prognathism and dentition
Cerebral Cortex - change in relative size
Large & complex brain for body size – greater information processing
Human brain:↑ in size (volume) Av size 1350cm3
Frontal lobe: 47% of total surface area (cf 33% apes) – thinking, problem solving, planning, processing, motor functions,memory
↑ in convolutions (folds) = ↑surface area = ↑in cerebral cortex size
Effects on primate way of life: ……
Endocast
an impression of the inside of the brain case, to determine volume/ size/ cranial capacity = 1350 cm3
(Can determine cc + no. of convolutions +
frontal lobe size / development from endocast)
Mobility of Digit
Primates have unspecialised pentadactyl (5 digits) limbs
Grasping or prehensile digits (to climb, swing in the trees, arboreal lifestyle.
Opposable thumbs and big toes (except humans – lost when foot became weightbearing.
Manual dexterity: ability to coordinate hand, finger movements to grasp + manipulate objects
Human hand is short and broad, with short straight fingers, long + strong thumb
Precision grip: able to grasp objects with precision eg writing pen, needle when sewing versus power grip.
Nails
– flattened out to protect tip of finger, better grip, no claws (claws limit grasping)
Friction ridges (fingerprints)
to allow better grip between digits + object.
Ridges in skin = increase grip
Patterns unique to individual
9 adaptions for bipedalism -Locomotion
Position of foramen magnum
Curvature of spinal column
The jaw
The pelvis
The knee
The foot
Centre of gravity
Muscle tone
Striding gait
Position of foramen magnum
opening beneath the cranium through which the spinal cord passes.
This allows the skull to balance on top of the vertebral column
Curvature of the spinal cord
Smooth C’ shape curve ----- S’ shaped
Human: double curvature achieved by lower vertebrae in lumbar region
Cervical curve – brings vertebral column directly under centre of gravity of the skull
The Jaw
size + protrusion of jaw reduced.
Apes – show prognathism - protruding jaw. Humans flatter facial profile
mainly due to softer food, large jaw for chewing tough plant material not
needed.
Change allows skull to balance on top of spine because, weight in front = weight behind.
Balance achieved with minimal muscular effort
The Pelvis
Broader + shorter from top to bottom
Bowl-shaped – (i) supports the abdominal organs when standing,
(ii) provides greater stability for bipedal walking (iii) supports developing foetus during pregnancy
F (broader than M) —à passage of infant at birth
Broad hip bone —-àattachment for large buttock muscles import. in leg movement and keeping upper body erect
The Carrying Angle
Hip joint is directly under trunk + head —– weight of body transferred from pelvis to legs
Large head of femur – fits into the acetabulum.
Pelvis broad-hip sockets far apart, but femurs tend to converge towards the knee
Femur forms angle= carrying angle
Ensures weight distribution remains close to the central axis of the body when walking.
Allows for greater stability in upright posture
When walking: body rotates about the lower leg + foot + each footstep follows a straight-line.
Striding gait – a way of walking in which the hip + knee are fully extended.
6) The Knee
bipedal species: weight of body transferred down the outside of the femur to the knee.
Knee joint = 2-part hinge joint, with 1 hinge on either side of the cruciate ligaments in the middle of the joint. Weight is transmitted to outer hinge – (of femur + tibia) it is larger + stronger than the inner one.
7) The foot
From knee – most of body weight(BW) transmitted through tibia to ankle
(Tibia larger + stronger than fibula
Big toe – large + aligned with others
Foot has 2 arches: longitudinal - runs front to back, transverse - runs side to side (this one unique to humans)
Arches absorb energy as the foot comes down, which enables the foot to be pushed back up again like a spring recoil \
Non-opposable big toe for weight bearing
Centre of Gravity (CofG)
Humans: legs longer than arms, this ↑ the length of stride when walking
This also ↓ centre of gravity
The lower the CofG =more stability
) Muscle tone
Muscle tone - the partial contraction of skeletal muscles to ensure the body is kept in an upright position/stance.
Striding gait –
walking upright in such a way that the hip and knee are fully straightened.
When a step is taken weight is transferred from (1) heel — along (2) outside of the foot to (3) ball of foot — across ball of foot (via transverse arch) to (4) big toe then, big toe thrusts off.
Advantages of bipedalism 6
A more energy efficient means of moving
Leaves the hands free to use tools
Leaves the hands free to carry items
Upright stance achieves greater height – can see further
Upright stance means – less of the body exposed to sunlight
Upright stance - ↑ exposure to breezes, increasing body cooling mechanisms
diastema
– have a gap
Molar teeth evolved from
3-cusps (early mammals) —– 4-cusps upper molars (+) —- 5-cusps lower molars (Y)
Evolved from mainly fruit diet of the ap
During Evolution of primates the (4)
Diastema has been lost
The number of teeth and prognathism has ↓
The number of cusps on the molars has ↑
The jaw has become more parabolic in shape
The Laetoli footprints
The Laetoli footprints are evidence that early hominins existed over 3 million years ago. Although there have been a number of interpretations of these footprints, with different numbers and sexes for the individuals who made them, most scientists agree that they were made by Australopithecus afarensis (a separate species of australopithecines) 3.56 million years ago. The footprints indicate a bipedal form of locomotion.
‘Lucy
‘Lucy’ is a female skeleton that was 40% complete. ‘Lucy’ has been classified as Australopithecus afarensis based on evidence gained from the dental arcades, the size of the canines and the prominence of the cusps on the cheek teeth.
