Hominid Evolution Flashcards
primate
closest living relative of our own species e.g chimp,, close ancestor/relative
characteristics of primates
- body is not specialised for particular environment
- limbs are generally unspecialised
- pentadactyl fingers
- nails instead of claws
- grasping fingers and toes with friction ridges for gripping
- first digit opposable
- forward facing eyes for 3D (stereoscopic) vision, able to distinguish colour
- poor sense of smell
- four incisors in both upper and lower jaw
- large and complex brain, cerebrum size increases as primates become more highly evolved
- not restricted to breeding season, rhythmical sexual cycle, usually one offspring at a time, long period of parental care for offspring
hominid
member of family of homindae includes humans and other apes
characteristics of hominids
- large complex brain, increased cognitive ability
- five cusps in molar teeth of lower jaw
- arms that move freely at shoulder
- wide shallow chest cavity
- no external tail
- have appendix
- diurnal: only active during the day
changes in relative size of cerebral cortex
- larger brain: as a result of arboreal (living in trees) environment, would have allowed more accurate visual and tactile perception as well as better coordination between sensory stimuli and muscular response
- reliance on vision to move and locate food generates large amounts of sensory info that must be processed and stored (done by cerebral cortex)
- progressive expansion of cerebral cortex has resulted in it covering the rest of brain
- human brain size ranges from 900-2200 cm cubed, but averages 1350cm cubed
- frontal lobe has greatest enlargement in surface area, makes up most of cortical surface and responsible for higher function of thinking, planning, reasoning, processing
- strong pattern of of convolutions that enable surface area of cerebral cortex to be increased cerebrum becomes larger and more convoluted as we evolve
- tool making involves predetermined image of what completed tool will look like so only possible with highly developed brain
cerebrum
part of the brain responsible for complex functions: vision, memory, reasoning, and manipulative ability
mobility of digits
- pentadactyl: have 5 digits on each limb and highly mobile
- prehensile: grasping refers to digits that can grasp (essential for climbing trees)
- evolutionary trend toward increasing ability to move digits independently
- big toe is not opposable, lost opposability when it became a weight bearing
- high mobility of digits allows humans to manipulate objects with greater skill
- human hand is short and broad with short straight fingers and long strong thumb, gives thumb great degree of freedom allows precision grip (holding pen, small delicate objects) and power grip (happens when thumb and fingers apply force against palm
locomotion
- change from quadrupedalism to bipedalism
- position of foramen magnum: where n joins the spinal cord, has gradually moved forward and became more central, weight of skull bone is held by vertebral column so large neck muscles are not required
- curvature of the spine: during evolution curvature of spine has changed to allow upright posture from C shaped curve in apes to S shaped in humans: improved body balance on top of neck
- double curvature of spine is achieved by vertebrae in lumbar region being wedged from front to back
prognathism
having a protruding jaw, during evolution size and protrusion of jaw has decreased this is important in allowing the skull to balance on top of spine
pelvis
- broader and shorter from top to bottom, and bowel shaped which supports abdominal organs when standing straight, provides greater stability for bipedal locomotion and in females supports foetus
- broad hip bones provide space for attachment of large buttocks muscles which move legs and keep body straight
carrying angle
- shape and orientation of pelvis results in hip joint being directly under trunk and head, allows weight of body to be transferred from pelvis to legs
- femur bone is large and fits into hip socket of pelvis, femur converges toward the knees this arrangement of femur forms an angle to the vertical ensures weight distribution remains close to central axis of body
- in humans weight tends to fall through outside of femur whereas in othe apes reverse is true
- carrying angle allows greater stability and when walking enables body to be rotated about lower leg and foot and each footstep follows more or less straight line enables humans to have striding gait instead of swaying from side to side like gorillas do when walking on two legs
knee
in bipedal species weight of knee is transmitted down to outside of femur to knee, knee joint is two part hinge joint which one hinge on either side of ligaments, weight is transmitted to outer hinge and it is larger and stronger than inner
- weight is transmitted down outside of each leg and centre of gravity falls in front of knees produced joint that requires no energy to support body in standing position
foot
from knee weight of body is transmitted from through tibia to ankle tibia is larger and stronger and weight is transmitted to ankles to tarsals then metatarsals then phalanges via arches o foot
- metatarsals are shaped in a way they form two arches: longitudinal arch: running from front to back and transverse arch: running from side to side (unique to humans), have enables humans to perfect bipedalism
striding gait
walking upright in a way that hip and knee are fully straightened, when foot hits groin weight is transmitted from heel along outside of foot, crosses ball of foot via transverse arch and carried by big toe
- when walking trunk rotates about pelvis forward swinging of arms compensates for natural rotation of body, swinging arms reduces amount of energy spent
advantages of bipedalism
- more energy efficient means of movement
- hands are free to use tools and carry items,
- upright achieves greater height and ability to see further, less of body is exposed to sunlight: increases exposure to breeze and increased cooling mechanisms
