B3. 6

B3. 6

Biological Evolution
1. Trends in the biological evolution of the:
  1. Hands
    1. The thumb is long and fully opposable enabling precision grip. Used fro making and using tools. Finger bones are straight and short in comparison to an ape.
  2. Foor
    1. 1. The shape of the foot has changed to become a platform. The toes are short, with the big toe beside the others and forward thrusting (i.e. non-opposable)
    2. The weight is placed on the outer edge with the inner side elevated into an arch. This provides a shock absorber effect and a spring that facilitates long distance travelling
  3. Brain
    1. Increased in complex linkages between brain cells, learning grows new connections
    2. Outer cortex, the amount of folding has increased by 40% which has increased the surface areas of the brain
    3. Frontal lobes, seperates us from neanderthals it is the seat of imagination, memory, creativity and abstract thought
    4. Speech in relation to the brain
      1. Wernickes's area is the section of the human brain that is involved in the understanding and comprehension of spoken language
      2. Broca's area is the section of the human brain that is involved in language processing speech production and comprehension
    5. Diet in relation to brain size
      1. Cooking food- easier to digest, bacteria in meat is destroyed resulting in a better quality diet
      2. Hunting lead to more meat in our diets= more protein
  4. Skeleton in relation to bipedalism
    1. Post-cranial
      1. Rib cage
        Flattened from front to back which moves the centre of gravity closer to the spine which improves balance.
      2. Spine shape
        CHanged from a 'C' shape to 'S' shaped. This allows the weight of the chest to sit above the pelvis rather than further forward. This improves both balance and absorbs the shock of walking.
      3. Pelvis Shape
        The pelvis has become short and more bowl shaped. this results in= improved balance, the support of the upper body,enlarges the valgus angle. The bowl shape also enlarges surface area for muscle attachment of the gluteus maximus.
      4. Femur length and shape
        The femur is longer and angled inwards from the hip so that the knees nearly touch(increased valgus angle). This assists the upper body to be positioned above the centre of gravity for walking.
      5. Knee joint
        The bottom of the femur has a buttress bone called the lateral condyle, that stops the sideways deflection of thigh muscles during walking.
    2. Cranial
      1. Position of the foramen magnum
        Moved from the back to the centre of the skull- allows skull to balance on the top of the spine and less energy expenditure is required by the muscles in the neck to keep the skull upright.
      2. Position of the occipials condyles
        They have moved from the back of the skull to the middle of the skull to keep the head above the ventre of gravity
Survival advantages of Bipedalism
1. Efficient locomotion
  1. Bipedalism provides an energy efficient method which favours low speed and long distance movement
2. Seeing over the grass
  1. Being up right allowed humans to be able to see better over the tall grass. This may have helped them to spot predetors or locate carcasses at a distance.
3. Freeing the hands
  1. This would've allowed humans to: a) Carry objects such as tools and food(form where it was killed or gathered back to the home base) and allowed mothers to carry the babies as they became relatively hairless. b) Use objects including weapons and tools. An upright stance made wielding a stick or throwing a stone much more effective. c) Make tools and weapons this freed the hands would've encouraged the making and evelopment of tools.
4. Decrease in exposure
  1. The body is exposed to direct sunlight by about 70%, the upright position helps to cool the body in the hot climate of the African savannah.
5. Applicable to all: this is an advantage as it aids survival and increases chance of reproduction
Dispersal Theories
1. Out of Africa
2. Likely dispersal routes
  1. The likely dispersal of modern humans from Africa would've been through the Middle East to Europe/Asia. They may have interacted with other pre-existing hominin populations as they dispersed further, i.e. Neanderthal and Denisova. The The hominin populations would've been similar as they shared a common ancestor/ DNA link, and different as they subsequently evolved in different areas/ came under different selection pressures. Denisovans and Neanderthal are more similar as they share a more recent common ancestor/ DNA link, whereas modern humans share a less recent one.
3. Compare and Contrast nuclear DNA And mDNA
  1. mtDNA is more useful compared to the nuclear DNA to calculate genetic distances. mtDNA has a known rate of mutation therefore can be used as a molecular clock and therefore can be used to date the lat common ancestor/ how long ago speciation occurred. Because mtDNA is only inherited from the mother to the child whereas nuclear DNA involves processes such as crossing over/segregation/IA that mis up existing alleles. Because mtDNA is unaffected by selection pressures whereas nuclear DNA is subjected to environmental selection pressures.
4. Reasons for hominin populations genetic differences and similarities
  1. Different groups/populations (dispersed to) in different areas / habitats therefore cam under different selection pressures so evolved differently.

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	Created by hayley.dresser over 10 years ago