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Flashcards in Evolutionary trends in hominids Deck (75)
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1

Hominidae

- = hominids
- Family name
- Includes great apes and lesser humans

2

Homininae

- = hominines
- Sub-family name
- Includes gorillas, chimpanzees and humans

3

Hominini

- = hominins
- Extinct and modern humans
- It is used to separate gorillas and chimpanzees from humans

4

Great apes

orang-utans
gorillas
chimpanzees

5

Lesser apes

gibbons
siamangs

6

How do hominins differ from apes?

- In their appearance, structure and behaviour
- Hominins are relatively hairless and their structure allows for a fully bipedal stance and gait
- Hominins have a unique erect posture and striding gait
- Hominins also have a greater development of the brain, changes in the size and shape of their teeth, development of speech and sexual characteristics

7

Bipedal locomotion

walking on two legs with the body upright

8

What is an adaptation?

Characteristics that help on organism survive and reproduce in its natural environment

9

Adaptations for an erect posture

- To stand upright and walk with a striding gait, humans require a modified muscular and skeletal structure
- These are considered adaptations as our erect posture helps our human ancestors to survive

10

Types of postural adaptations

1. Position of the foramen magnum
2. Curvature of the spine
3. Jaw size
4. Pelvis shape
5. Carrying angle of the femur
6. Knee structure
7. Foot structure
8. Centre of gravity

11

Foramen magnum

- Large hole at the base of the skull in which the brain joins the spinal cord
- In humans, it is directly under the skull
- In quadrupeds, it is 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-human require much stronger neck muscles to hold the head in position

12

Spine curvature in non-humans

- Non-humans have their vertebrae arranged in a single (C shaped) curve, causing the body to tilt forwards
- Their centre of gravity is in front of its hind feet

13

Spine curvature in humans

- Humans have a double curvature, giving them an S shaped spine which contributes to an upright stance
- The vertebrae in the lower, or lumbar region are wedge-shaped from front to back, thus forming a forward-jutting curve. This improves body balance in the upright position
- It enables the head to balance on the top of the neck
- The curves bring the head directly over the spine, this means that the centre of gravity runs straight through the head and spine

14

Pelvis shape

- The pelvis in humans is broader and shorter than that of other primates
- The human pelvis supports the abdominal organs during upright stance
- Broad hip bones provide space for the attachment of large buttock muscles, which move the legs and keep the upper body erect

15

Position of the hip joint (humans)

- The hip joint is directly under the head and body trunk (when we walk)
- This allows the weight of the body to be transferred to the legs

16

Pelvis and femur structure

- The pelvis is wide with two acetabulum
- The head of the femur is large and first into the acetabulum
- Femurs converge towards the knees
- Femurs are not directly vertical

17

Carrying angle

- The angle the femur makes with the knee joint
- Ensures that the weight distribution remains close to the central axis of the body when walking
- During walking, it enables the body to be rotated about the lower leg and foot, producing a striding gait (instead of swaying from side to side)
- Weight is transmitted through the outside of the femur

18

The knee

- The weight of the body is transmitted down the outside of the femur to the knee
- The knee consists of two ‘hinges’ with the ligaments in between (e.g. ACL)
- The outer hinge is larger
- Although the weight of the body is transmitted down the outside of the knee joint, the centre of gravity falls through a lone just in front of the knee (when standing)
- This force tries to bend the knee backwards, but the knee ligaments naturally resist it
- Therefore, no energy is required to support the body in a standing position

19

The foot

- Does not have an opposable toe
- No longer prehensile
- Human have both a longitudinal and a transverse arch
- Non-humans have only a longitudinal arch
- The arches facilitate a striding gait
- These two arches have enabled humans to perfect bipedal locomotion

20

Centre of gravity

- Apes have much longer arms and their legs are relatively short
- Shorter arms and longer legs in humans lower the human centre of gravity
- Apes → chest level
- Humans → pelvis level
- A lower centre of gravity gives greater stability during striding
- Longer legs in humans facilitates longer steps when striding

21

Stance and locomotion

- Hominins have an upright stance and a striding gait
- All homo-genera (habillis, erectus and neanderthalansis) and Australopithecines were upright

22

Muscle tone

- The partial contraction of many skeletal muscles
- Facilitated posture
- Sleep reduces muscle tone
- Humans require sustained muscle tone to support and upright stance

23

Areas with muscles that support the upright stance

- Spine
- Hip
- Knee
- Ankle
- Abdomen

24

What areas work together to maintain postural equilibrium?

The nervous system (sensory tract of the cerebral cortex) and sense organs

25

Knee extension

- In a striding gait, hominins have their hips and knees fully extended (straightened)
- Even when bipedal, apes have their knees bent and their bodies bent forward at the hip

26

Weight transmission

- 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
- The toe is parallel, as it is used for weight bearing rather than grasping

27

Rotation of the trunk

- With each stride, the trunk rotated about the pelvis
- Arms swing to oppose this rotation keeping the shoulders perpendicular to the direction of travel
- This reduces the need for energy to reverse trunk rotation

28

Footsteps

- Each footstep can follow in a straight line
- Apes lack a wide pelvis and carrying angle
- When bipedal, apes must swat from side to side so that the weight is over each leg in turn

29

Average human brain size

1350 cm3

30

Average ape brain size

200-500 cm3