Primate evolution Flashcards
What are the features that all primate have
Body: not specialised, generally erect posture
limbs: unspecialised, flexible=more movement
hands/feet: pentadactyl (5xfingers/toes), nails (no claws), grasping fingers/toes w/friction ridges for gripping, first digit opposable
eyes: fwd facing=stereoscopic vision (increase depth perception), able to distinguish colour
sense of smell: poor
teeth: 4xincisors in upper/lower jaw
brain: large and complex, cerebrum size increases as primate becomes more evolved
reproduction: rhythmical sexual cycle, usually one offspring at time, long period of parental care
Describe how humans are classified as primates
Humans as primates are great apes. Part of the same family (Hominids).The species vary within this family due to change in DNA sequences
How do you differentiate between great apes and other primates
-larger, more complex brain than other primates (enables increased cognitive ability)
-five cusps in molar teeth of the lower jaw
-arms that can freely rotate at shoulder
-wide shallow chest cavity
-no external tail
-an appendix
-diurnal (active during the day)
How does variation in hominids come about
Via change to:
-relative size of cerebral cortex
-mobility of digits
-locomotion-adaptation to bipedalism/quadrupedalism
-prognathism and dentition
What is the evolutionary trend for the cerebral cortex
-47% of cortical surface is frontal lobe for humans while 33% is frontal for apes (higher functioning area of brain)
-increase brain size=increased depth+number of convolutions of cerebral cortex=increase SA
-anew ability of creating, not just using tools
-larger brain=increase cranium capacity-more skull used by humans to house brain
-humans lack a prominent brow ridge
-shortened snout=flat face with more prominent nose
Describe the evolutionary trend for mobility of digits
-increased mobility + independent digit movements
-first digit opposability+relatively longer than other digits
-claws give way to nails, thus human have no claws
-humans lack big toe opposability due to weight bearing bipedalism
-more mobility allows for manipulation of objects with great skill and precision grip
Describe the evolutionary trend for locomotion
Change overtime from quadrupedalism to bipedalism acted as a selective pressure during natural selection, allowing human ancestors to survive.
What are the adaptations for erect posture
-position of foramen magnum (centre vs back)
-curvature of spinal column (S vs C)
-centre of gravity
-jaw, pelvis, carrying angle, knee, foot
Describe the evolutionary trend of the foramen magnum
Hole where brain joins spinal cord
-position has gradually moved forward to become more central
-for humans: centre=no large neck muscles and skull balance on top of spine
-for gorillas: towards back=large neck muscles to hold head)
Describe the evolutionary trend for curvature of the spinal cord
-humans: double curvature (s-shaped) allowing upright position
-lumbar vertebrae wedge shaped
-improved balance, head on top of neck
Describe the evolutionary trend for the jaw
-change to flatter profile
-apes had protruding jaw=prognathism
-due to gradual reduction, skull balances better on top of spine
-less muscular effort to hold head
Describe the evolutionary trend for the pelvis
-broader/shorter in humans (wide)
-long/narrow in apes
-wider in females to allow infant passage during birth
-the gradual widening of pelvis allows attachment of muscles to move legs bipedally and keep erect posture
-support abdominal organs=less strain on abdominal muscles to hold in place
Describe the evolutionary trend for the carrying angle
-increases in femur
-pelvis shape (broad/short) allows hip joint to be directly under trunk and head
-wide pelvis allows femur (w/larger head) to converge twds knee (femur angled twds knee forms carrying angle)
Describe the evolutionary trend for the knee
-weight distribution remains close to central axis (centre of gravity falls in front of knee) and outside of knee
-good stability for walking (body can rotate about lower leg, footsteps follow straight line, creates striding gait)
-ligaments create resistance to knee bending bwds+outer ligament larger+stronger
-joints therefore need no energy to support standing position
Describe the evolutionary trend for the foot
-weight transferred from knee-tibia-ankle
-no prehensility
-big toe=larger inline with other digits
-metatarsals shaped to form 2x arches: longitudinal arch (front to back) and transverse (side to side)
-perfect bipedal locomotion
Describe the evolutionary trend for centre of gravity
point at which weight of body concentrated
-humans have longer legs than arms (increase stride length + lowers centre of gravity)
-lower centre of gravity creates stability during bipedal locomotion and standing erect
Describe the evolutionary trend for muscle tone
partial contraction of skeletal muscles
-supports upright position in hips, knees, ankle, abdominal and spine
Describe the evolutionary trend for striding gait
-full extension of hip and knee into straight position
-hominins are only animals w/this locomotion
-foot evolved to be weight bearing
How does striding gait occur
- Foot hits ground
- Weight transmitted form heel along outside of foot
- Weight crosses ball of foot
- Then to big toe
-trunk rotates about pelvis
-right arm swings fwd as left leg extends
Describe some advantages of bipedalism
-energy efficient means of moving
-hands free to use tools and carry items
-upright stance achieves height=ability to see further, less of body exposed to sunlight, increased exposure to breeze=cooling mechanism
Describe the evolutionary trend for number and shape of teeth (dentition)
-gradual decline in tooth size (canines especially)
-parabolic dental arcade
-decrease in number of teeth (due to reduction in jaw/face size)
-no diastema
Describe the evolutionary trend for prognathism and brow ridges
-fwd jutting jaw has decreased to flat face
-decrease in brow ridge size
-more prominent nose
-flatter face=central weight position=skull can balance during upright stance
-as size of frontal lobe increases, brain occupies more=reduced brow ridge
Define brachiation
What are it’s adaptations?
Arboreal locomotion. Movement accomplished by swinging from one hold to another by arms.
-longer arms than legs and flexible shoulder joints
-long, strong finger for grasping and holding body weight
