Human evolutionary trends

Question 1

Hominid

Answer 1

Any member of the group consisting of all modern and extinct humans and great apes (including gorillas, chimpanzees and orangutans) and all their immediate ancestors

Question 2

Naming organisms

Answer 2

Named according to the genus and species to which they belong (E.g homo sapiens belong to the genus homo and species sapiens)

Question 3

Hominid evolutionary trends

Answer 3

Directional change in a character state, or set of character states, resulting in a significant change through time: Relative size of cerebral cortex, Mobility of the digits, Prognathism and dentition, Locomotion- adaptions to bipedalism and quadrupedalism

Question 4

Evolution in the relative size of the cerebral cortex

Answer 4

An average increase in cerebrum, in particular the cerebral cortex (frontal lobe), Cerebral cortex is important for its role in vision, memory, reasoning and manipulative ability, A larger cerebral cortex facilitates more accurate visual and tactile perception along with better co-ordination, Both have increased enormously as primates have evolved, Number of cerebral convolutions has also increased dramatically as primates have evolved, Greater surface area of cortex has had far-reaching effects on development (tool making and use, behavioural responses, greater survival chance)

Question 5

Evolution in the mobility of digits

Answer 5

Primates are pentadactyl, Digits are highly mobile due to arboreal (living in trees) ancestry and prehensile (capable of grasping), Evolutionary trend is toward increasing ability to move digits independently of one another, thumb is most evolved, Thumbs are independent and opposable (can be placed opposite the fingers of the same hand), There have been varying degrees of opposability throughout evolution (longer the relative length of the first digit, the more opposable it is)

Question 6

Opposable thumb

Answer 6

Allow the digits to grasp and handle objects which enables a precision grip

Question 7

Power grip

Answer 7

Any carrying or grasping task where the finger flex toward the palm, most forceful grip available to the human hand and allows gross motor skills

Question 8

Precision grip

Answer 8

When an object is pinched between the thumbs and fingers

Question 9

Evolution in prognathism

Answer 9

A projecting lower jaw or chin, Human jaw is smaller and less-prognathic than in the ape groups

Question 10

Evolution in dentition

Answer 10

Dental arcade in humans- parabolic with all teeth very similar in height, Dental arcade in apes- have parallel sides, large canines and diastemas, Trend- towards smaller, more uniform teeth in hominins

Question 11

Locomotion

Answer 11

Humans require a modified muscular and skeletal structure to stand upright and walk with a striding gait, These modifications are considered adaptions (characteristics that help an organism survive and reproduce in its natural environment)

Question 12

Postural adaptations (6)

Answer 12

Position of foramen magnum and prognathism, Curvature of spine, Pelvis shape, Carrying angle of femur, Knee structure, Foot structure

Question 13

Foramen magnum

Answer 13

Large hole at the base of the skull, In humans- directly under the skull, In quadrupeds- further towards the back of the skull, Having the foramen magnum directly under the skull enables the skull to balance on the top of the vertebral column, Non-humans require much stronger neck muscles to hold the head in position, Because the human jaw is smaller and less-prognathic, the skull can balance on the spine as the weight in front of the foramen magnum is approximately the same as the weight behind it

Question 14

Spine curvature

Answer 14

Non-humans have their vertebrae arranged in a single (C-shaped) curve meaning the body tilts forward and its centre of gravity is at chest level, Humans have a double curvature (S-shaped spine), Lumbar vertebrae are wedge-shaped, providing a strong lumbar curve which brings the head directly over the spine meaning the centre of gravity runs straight through the head and spine

Question 15

Pelvis shape of humans

Answer 15

Broader and shorter than that of other primates, Supports the abdominal organs during upright stance, Broad hip bones provide space for large buttock muscles to attach, Broad pelvis allows the femurs to attach further apart

Question 16

Carrying angle

Answer 16

Angle away from the vertical, ensures that the weight distribution remains close to the central axis of the body when walking, allows the body to be rotated about the lower leg and foot, Enables the body to be rotated about the lower leg and foot, producing a striding gait (instead of swaying) when walking

Question 17

Evolution in carrying angle

Answer 17

Hip joint is directly under the head and body trunk allowing the weight of the body to be transferred to the legs, Pelvis is wide with two acetabular, Head of the femur is large and fits into the acetabulum, Femur converges towards the knees and is not directly vertical, Weight is transmitted through the outside of the femur, Means each footstep can follow a straight line, Apes lack a wide pelvis and carrying angle meaning, when bipedal, they must sway from side to side so that the weight is over each leg in turn

Question 18

Evolution of the knee

Answer 18

Weight of the body is transmitted down the outside of the femur to the knee, Consists of two ‘hinges’ with the ligaments between, Although the weight of the body is transmitted down the outside of the joint, the centre of gravity falls through a line just in front of the knee, Force tries to bend the knee backwards, but the knee ligaments naturally resist it meaning no energy is required to support the body in a standing position, Unlike apes’ knees that are always flexed, human knees are capable of full extension and they lock into place when the other leg is in swing phase, providing a stable supporting leg

Question 19

Larger knee hinge

Answer 19

Accommodates the carrying angle as weight is distributed through the outside of the femur

Question 20

Foot structure of humans

Answer 20

Humans feet have changed dramatically from a mobile, grasping structure to a rigid, supporting one, Human foot doesn’t have an opposable toe and is no longer prehensile, Human toes are parallel which provides a pedestal, Human heel bone is large and robust providing support for balance, Humans have both a longitudinal and transverse arch

Question 21

How foot structure helps walking

Answer 21

Big toe provides strength and push off during bipedal locomotion, Arches facilitate a striding gait and provide from spring and shock absorption, In a striding gait, the weight is transmitted from the heel along the outside of the foot to the ball of the foot, at the final moment of the stride, the weight is transferred to the big toe, Toes are parallel as they are used for weight bearing rather than grasping, Arms swing to oppose the rotation of the trunk around the pelvis keeping shoulders perpendicular to direction of travel which reduces the need for energy to reverse trunk rotation

Question 22

Laetoli

Answer 22

Name of a site in Tanzania where the footprints of three hominids were preserved in ash

Question 23

Muscle tone

Answer 23

Continuous and passive part contraction of muscles helps to maintain posture

Question 24

Adaptations for climbing trees (5)

Answer 24

Rotating shoulder joint, Short clavicle, high shoulder blades, Long arms/shorter arms to leg ration, Long curved fingers with long thumbs well adapted to grip branches/hang from branches

Question 25

Adaptations for climbing trees

Answer 25

Rotating shoulder joint, Short clavicle, high shoulder blades, Long arms/shorter arms to leg ration, Long curved fingers with long thumbs well adapted to grip branches/hang from branches

Question 26

Human brachiation

Answer 26

Due to the shape of the pectoral girdle, humans are the only living hominid that can throw objects accurately and at speed, Homo sapiens have a straight shoulder line whilst Australopithecines and chimpanzees have an upward curve to their shoulder line, Curved shoulder line supports climbing and suspension in trees

Question 27

Speciation (5)

Answer 27

Variation- present in individuals, wide variety of genes present, Isolation- isolation of gene pool/barriers to gene flow, Struggle- individuals with suitable genes are more likely to survive and produce off spring, Selection- only suitable genes are passed on, Speciation- no longer able to reproduce with others/new species