Ch. 18 Evolutionary Trends of Hominids Flashcards
what is the ranks of primate tribe
Hominidae (Hominids) (humans, orang, gorillas, chimps) >
Homininae (Hominines)(gorillas, chimps, humans) >
Hominini (hominins) (humans)
define adaption
any characteristic that helps an organism survive and reproduce in its natural environment
what are the 8 adaptions for erect posture
o Position of foramen magnum, curvature of spinal column, jaw, the pelvis, the carrying angle, the knee, the foot, center of gravity
what is the difference in position of foramen magnum between humans and apes
Humans
Located centrally underneath skull
apes= back
why did foreman magnum change position
(During evolution) FM gradually moved forward until skull is able to balance on top of vertebral column
what is the difference in neck muscles between humans and apes
Humans- Weight of skull is borne by vertebral column so large neck muscles not required
apes- Needs large neck muscles to hold head in position
what is the difference in curvature of spine between humans and apes
o Apes: C shaped
o Humans: Double curvature= S shape (contributes to upright stance)
what is a feature of the human spine, lumbar vertareb
- Humans developed: Vertebrae in lower, lumbar, region (small of back) = wedged shaped from front to back= forming forward- jutting curve
what are three things that the lumbar curve provide
o improves body balance in upright position
o enables head to balance on top of neck
o cervical curve in neck= brings vertebral column directly under center of gravity of skull
what is the difference in jaw between humans and apes
- Apes= Protruding Jaw
- Human= flatter facial profile
why did jaw reduce and become flatter (what did it allow)
o Change Important in allowing skull to balance on top of spine, because weight in front of foramen magnum is approx.. equal to weight behind
o // balance achieved with minimum muscular effort
what is the difference in pelvis between humans and apes
- pelvis in humans= broader + shorter from top to bottom than in apes
what does the bowl shape pelvis allow
supports abdominal organs while standing erect + females to support developing fetus during pregnancy
what does broad hip bones allow space for
- Broad hip bones= space for attachment of large buttocks muscles= which move the legs and keep upper body erect
why does the femur converge inward
Because pelvis= broad= hip sockets wide apart
what does the carrying angle allow
♣ Ensures weight distribution remains close to central axis of body when walking
♣ Allows for greater stability when walking as enables the body to be rotated about the lower leg and foot, and each footstep to follow more-or-less straight line
♣ Enables humans to have a striding gait instead of swaying side to side (as gorillas) when walking on two legs
where does weight transmission fall along legs in humans
outside femur
why is the outer hinge larger in humans
o Because weight transmitted to outer hinge= its larger + stronger than inner one
explain the natural resistance of the knee
- Although weight of body transmitted down outside of each leg, center of gravity tends to fall through a line just in front of knees
♣ = force that tries to bend knee backward but is resisted by ligaments making up knee joint
♣ This natural resistance produces knee joint that requires no energy to support standing body position
what is best evidence to show humans loss of prehensility in foot
toe aligned, non opposable
explain the two arches that enable bipedal locomotion
o Enabled humans perfect bipedal locomotion a. Longitudinal arch ♣ Running from front to back b. Transverse arch ♣ Running from side to side ♣ Unique to humans
define striding gait
- Humans walk bipedally using striding gait- walking in such a way that hip and knee are fully extended
what does humans having longer legs than apes cause
o Increase length of stride when walking
o Serve to lower center of gravity of body, the point at which all weight of body appears to be concentrated
why are human centre of gravity lower
- In contrast to humans (where almost half of total height= in leg length) ape only about one third of total height taken up in leg length
o Results in center of gravity being further up body
o Apes Centre of gravity at chest/ humans= level of pelvis
♣ Humans lower COGravity= contributes to stability when moving bipedally or standing erect
where is muscle tone evident
- Essential elements for maintaining upright stance= muscle tone
- mostly evident in muscles that support body in upright position
explain movement of apes (when compared to striding gait)
apes have bent knees and bodies bent forward at hips
what is the movement process of striding gait
foot hits ground, weight= transmitted from heel along outside of foot as far as ball, crosses ball (via transverse arch) and finally borne by big toe > whole weight of body propelled by big toe
what does swinging of arms allow
- When walking, trunk rotates about the pelvis
- Forward swinging of arms compensates for natural rotation;
o right arm naturally swings forward as left is extended and vice versa - Swinging of arms=
♣ keep shoulders at right angles to the direction of travel
♣ reduces amount of energy expended
o If arms did not move as they do, energy wasted in reversing rotation of body after each stride
why do apes not have carrying angle
lack wide pelvis + carry angle // must sway
difference in dental arcdade of humanoid and apes
humans= parabolic apes= u
why did brow ridge decrease
- Gradual enlargement of cranial portion of skull to accommodate increasing size of frontal region of brain= more distant forehead + reduction in size of brow ridge
SCASA: what are species within the great ape family differentiated by
dna nucleotide sequences
SCASA: what has the differences in dna nucleotide sequences resulted in differences of:
- relative size of the cerebral cortex
- mobility of digits
- locomotion (adaptations)
- prognathism and dentition
