chapter 18 - evolutionary trends of hominids

Question 1

what is a tribe

Answer 1

• classification between subfamily and genus
• hominini: humans and our distinct ancestors, separates us from chimps, gorillas, and their extinct ancestors (differ in appearance, structure and behaviour)

Question 2

what are characteristics of hominins and who was lucy

Answer 2

• erect posture, unique striding gait, increased brain development, bipedal locomotion
• lucy: fossilised footprints in laetoli, belong to extinct humans with bipedal locomotion (73 million years)

Question 3

describe the trends in human ancestors, australopithecus and homo

Answer 3

• human ancestors: first humans developed and evolved from ancestral ape
• australopithecines: genus australopithecus, first humans
• homo: evolved into homo habilus, erectus, neanderthals and eventually sapiens

Question 4

what is an adaptation

Answer 4

• any characteristic that helps an organism survive and reproduce
• erect posture: allowed for humans to survive, foramen magnum, curvature of spine, jaw, centre of gravity, pelvis, carrying angle, knee and foot

Question 5

describe the position of the foramen magnum

Answer 5

• opening beneath cranium through which spinal chord is located
• H: located centrally underneath skull, gradually moved forward so skull can balance on top of vertebral column, don’t need large neck muscles
• A: located towards the back of the skull, need large neck muscles to hold up skull

Question 6

describe the curvature of the spine

Answer 6

• H: have a double curvature (s), contributes to upright stance
• lumbar vertebrae: wedge shaped, forming forward jutting curve to improve balance in upright position, enables head to balance on spine
• cervical curve: brings vertebral column directly under centre of gravity of skull

Question 7

describe the jaw

Answer 7

• H: flat facial profile, reduced in size to allow for skull to balance on top of spinal column, weight on either side of the foramen magnum is equal, reduces muscular effort
• A: protruding jaw, foramen magnum behind, increased weight / size of jaw leads to very large neck and shoulder muscles

Question 8

describe the pelvis

Answer 8

• H: broader, shorter, bowl shaped (supports organs during upright position)
• broad hip bones allow for attachment of muscles that move legs and keep body upright
• A: longer and skinnier, don’t need to support upper body as much

Question 9

describe the carrying angle

Answer 9

• arrangement of thigh bones to form an angle to vertical
• H: hip sockets are wide apart but femur converges towards knees, allows transferral of weight from pelvis to legs
• weight distribution: kept to central axis when walking
• stability: increased, body rotates around lower leg / foot, straight line footstep
• striding gait: rather than sway, weight transmission falls outside femur
• A: does not form angle, femur is directly over knee, weight transmission falls inside femur

Question 10

describe the foot

Answer 10

• transmission: knee, tibia, ankle, talus, tarsals, metatarsals, phalanges (via arch)
• human: distinct adaption to bipedal locomotion, lost prehensility / opposability, big toe is large and alongside others (parallel)
• arch: longitudinal (shape of tarsals) and transverse arch (unique to humans)
• striding gait: hip and knee are fully extended
• apes: opposable toe (abboreal), longitudinal arch is minimal

Question 11

describe the knee

Answer 11

• A: centre of gravity is away from knee, no force, not weight bearing, joints are same size, not able to be straightened
• H: weight of body is transmitted down outside of femur to knee, knee has two part hinge (outer is larger), centre of gravity falls just in front of knee, force that tries to bend knee backwards (resisted due to ligaments)

Question 12

describe the centre of gravity

Answer 12

• COG: point through which the mass of the body is considered to act
• H: longer legs than arms (1/2), COG at pelvis, contributes to stability
• A: shorter legs (1/3) COG higher up at chest (move on all fours)