hominid evolution Flashcards
order
Primates:
Primates include tarsiers, lemurs, lorises, monkeys, apes and humans
Family
Hominidae
Hominids include all modern and extinct orangutans, gorillas, chimpanzees and humans
Tribe*
Homini:
Hominins include extinct ancestors of humans and modern humans
Genus
Homo:
Homo includes some extinct ancestors of humans and modern humans
Species
sapiens:
Homo sapiens are modern humans
are there a singular characteristic that can be used to separate the primates from all other mammals
no
what are most features of a primate a result of?
having evolved in an arboreal, or tree-like, environment.
primate characteristics: body
not specialised for a particular environment
primate characteristics: limbs
Generally unspecialised
primate characteristics: hands/feet
Pentadactyl - five fingers or toes
Nails instead of claws
Grasping fingers and toes with friction ridges for gripping
First digit opposable
primate characteristics: eyes
Forward facing for three-dimensional (stereoscopic) vision
Most are able to distinguish colour
primate characteristics: Sense of smell
Very poor
primate characteristics: Teeth
Four incisors in both the upper and lower jaw
primate characteristics: Brain
Large and complex
Cerebrum size increases as primates become more highly evolved
primate characteristics: Reproduction
Not restricted to a breeding season
Rhythmical sexual cycle
Usually only one offspring at a time
Long period of parental care for offspring
humans are in same family as?
great apes (orang, chimp, gorilla, bonobos)
characteristics all species in the family Hominidae share
- larger, more complex brain than other primates → increase cognitive ability → recognise self in a mirror
- five cusps in the molar teeth of the lower jaw as diet was mainly fruit
- arms that can freely rotate at the shoulder
- wide, shallow chest cavity
- no external tail
- an appendix
- diurnal (active during the day)
variations that reflect changes in the DNA nucleotide sequences during evolution
- relative size of the cerebral cortex
- mobility of digits
- locomotion – adaptions to bipedalism and quadrupedalism
- prognathism and dentition
the cerebrum progressively ___________ in size
increased (especially cerebral cortex)
change in cerebrum size results
- higher-order functions (vision, memory, reasoning, manipulative ability)
- necessary to cope successfully with environmental change
why did primates have large brains for their body size
- due to tree dwelling environment
- pressure of natural selection in arboreal environ. → favoured more accurate visual and tactile perception, better coordination b/w sensory stimuli + muscular response
- reliance on vision to move, locate and manipulate food → large amount of complex sensory info to be processed and stored (carried out by cerebral cortex)
- pressure of natural selection in arboreal environ. → favoured more accurate visual and tactile perception, better coordination b/w sensory stimuli + muscular response
apes average cerebral cortex size
b/w 400-500 cm
which lobe had the greatest enlargement in surface area and why?
frontal lobe; higher functions – thinking, reasoning, planning
Pattern of convolutions (folds) purpose
Enable surface area of brain to be increased
Effect on life of primates due to increase in size of CC
- Move around and locate food
- Develop social skills
- Tool making
- Involves predetermine image of what completed tool should look like (higher skill)
- Greater variety of behavioural responses to meet variety of problems
- Most primate species → daily life involves interactions with relatives, allies, adversaries
- Mutual cleaning and grooming → reinforce relationships
- Threats → lead to fighting → maintain hierarchy of dominance
- Behavioural flexibility taken place of further physical specialisation
- Most primate species → daily life involves interactions with relatives, allies, adversaries
was the Early hominin brain fossilised
no
endocast
an impression of the inside of the brain case, either artificial or natural, made of rock or some other solid material
purpose of endocast
determine brain size by measuring volume inside cranium using an endocast = cranial capacity
two areas of the brain have become highly developed in modern humans
- broca’s area
- wernicke’s area
broca’s area
speech production
Controls the muscles of the lips, jaw, tongue, soft palate and vocal cords during speech
wernicke’s area
comprehension of language - ability to listen
Pentadactyl
5 digits on each limb
Digits are highly mobile why?
related to arboreal way of life
why are prehensile digits essential?
essential for climbing, wrapping long curved digits around branches of trees
Evolutionary trend of the mobility of digits
increasing ability to move digits independently of one another
which digits were most highly developed
Thumb and big toe
Opposability
first digit can be moved in such a way that it can touch each of the other digits
what does opposability depend on
Depends on relative length of the first digital compared to other four
how did primates lose opposability
Lost opposability when human foot became weight bearing rather than grasping
precision grip
Humans have longest thumb of all primates → allows us to manipulate objects with our hands
quadrupedalism
walking on four limbs
bipedalism
walking on two legs
bipedalism is an adaptation that…
that helps human ancestors to survive → acted as a selective pressure during natural selection
Foramen magnum
where the brain joins the spinal cord through a hole in the skill
what happened to the foramen magnum due to evolution
Gradually moved forward to become more central (due to evolution of modern humans)
- Allows skull to balance of top of vertebral column
Gorilla foramen magnum position
needs large neck muscles to hold head in position
humans foramen magnum position
weight of skull is born by vertebral column→ large neck muscles not required
Curvature of the SC Evolution (structure)
Smooth C shaped curve (apes like gorillas) → evolved to S shaped curve (double curvature)
curvature of the SC Evolution results
allow upright posture
- Improves body balance in upright position
- Enable head to balance on top of neck
jaw for apes and humans
- Apes = protruding jaw (prognathism)
- Humans = flatter facial profile
evolution effects on the jaw
- Size and protrusion reduced due to evolution
- Allows the skull to balance on the top of the spine (weight in front of FM is = to weight behind it)
- Balanced achieved with min of muscular effort
humans pelvis structure
broader, shorter from top to bottom, bowl shaped
humans pelvis benefits
- Bowl shaped supports abdominal organs when standing erect
- Provides greater stability for bipedal locomotion
- Supports developing foetus during pregnancy
- Broad hip bones provide space for attachment of large buttock muscles → move legs; keep upper body erect
the carrying angle
shape and orientation of the pelvis → hip joint being directly under the trunk and head
what does the carrying angle allow for?
- Allows the weight of the body to be transferred from pelvis → legs
- Allows for greater stability in an upright posture
changes to femur due to evolution
- Head of femur is larger, fits into acetabulum of pelvis
- Pelvis is broad → hip sockets wide apart→ femurs converge towards knees
- Femur arrangement forms angle to the vertical = carrying angle
weight distribution due to changes to femurs
- Ensures the weight distribution remains close to the central axis of the body when walking
- Weight tends to fall through the outside of femur (reverse in apes)
what does walking enable?
- enables the body to be rotated about the lower leg and foot; each footstep follows a near straight line
- Allows humans to have a striding gait instead of swaying from side to side like gorillas or chimps when walking on two legs
knee adaptation
- Bipedal species = weight of body transmitted down outside of femur → knee
- Knee joint = two-part hinge joint
Natural resistance
produces a joint that requires no energy to support body in a standing position
Centre of gravity
Centre of gravity of body tends to fall through a line just in front of knees → results in force that tried to bend knee backwards but resisted by knee ligaments
how is body weight transmitted at the ankle
From knee joint, most of body weight transferred through tibia → ankle
BW transmitted from tibia through talus (ankle bone) → other tarsal bones → metatarsals → phalanges via arches of foot
Human foot distinctive adaptation for bipedal locomotion
- Lost its grasping ability/prehensibility – now a highly specialised locomotory organ
- Seen in big toe
- Metatarsals shapes to form two arches (enabled humans to perfect bipedal locomotion)
- Longitudinal arch (front to back)
- Transverse arch (side to side)
effects of humans having longer legs than arms
- Long legs increase length of stride when walking
- Serve to lower centre of gravity of body (point at which all the weight of the body appears to be concentrated) – pelvis level
- Contributes to stability when moving bipedally/standing erect
location of centre of gravity for apes and humans
apes: Higher centre of gravity (chest level)
humans: lower centre of gravity (pelvis level)
Muscle tone
partial contraction of skeletal muscles