AS 91606 Human Evolution External

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Why was bipedalism so evolutionary?

: freed the hands, allowing us to take advantage of our larger brain

• more energy conserved for reproduction

• greater chance of survival

quadrapedialsm

: organisms that walk on all four limbs

bipedalism

: organisms that walk on two feet

environmental conditons that triggered bipedalism 

the tectonic plates of the earth were moved and the himalayas were formed as india moved up. weather conditions changed, therefore airflow changes, and africa changed from an abundant rainforest to a savannah

which two species experienced an evolutionary deadend in 3.9-2.5 mya? 

A. robustus and P. boisei

which hominin species provided evidence for bipedalism?

a.afarensis

• approx 4mya in rift valley

which hominin species began to develop tools? (inc. time frame)

h.ergaster (1.4 - 1.7 mya) 

which hominin species began the development of fire/discovered fire? (inc. time frame)

h.erectus

• 1.6 - 0.2 mya

where and when was lucy (a.afarensis) discovered?

in rift valley between kenya and ethiopia approx. 4 mya

forum magnum and the change that occured

a hole in the skull that balances the skull over the spine 

• centralised - changed from being positioned at the back of the head (apes)

explain the change in the forum magnum 

forward facing head means less muscle attatchment needed and center of gravity is more central

zygomatic arches and the change that occured

the cheekbones

• quadrapeds = LARGER zygomatic arches 

• bipeds = SMALLER zygomatic arches 

explain the change in the zygomatic arches

there is no need for really strong chewing muscles, muscle attatchment points, or teeth due to refined diet (throughout evolution)

sagittal crest and the change that occured

ridge at the top of the skull to which the jaw muscles are attached (also connected to the zygomatic arches and jawbone)

• quadrapeds = LARGE saggital crest 

• bipeds = NO sagittal crest

explain the change in the sagittal crest 

change in diet 

• less chewing, less jaw muscle required and therefore was decreased overtime (evolution)

brow ridge and the change that occured

heavy bone over the eyes to protect the eyes 

• quadrapeds = LARGE brow ridge 

• bipeds = NO brow ridge 

explain the change in the brow ridge 

initially, brow ridges were prominent due to powerful chewing action, causing stresses in the lower jaw. overtime, bipedalism meant skull stucture changed and therefore, brow ridges were no longer required

ribcage and the change that occured

structural framework that surrounds and shields vital organs

• quadrapeds = BROADER and WIDER

oriented more horizontally (facing the floor), larger gut and organs need more support 

• bipeds = TIGHTER and SMALLER

vertical to accommodate walking upright and lung function 

explain the change in the ribcage

quadrapeds to bipeds changed from leaning downward to standing upright

• shift in center of gravity (no longer on all fours but two feet) 

• optimized for upright locomotion and adaptation 

arm:leg ratio and the change that occured

length of arms to legs 

• bipeds display SHORTER arms and LONGER legs

• quadrapedals display LONG arms and LONG legs

explain the change that occured in the arm-leg ratio

• long arms were no longer for brachiating - no longer needed (evolutionary changed)

• quadrapeds required SAME arm:leg ratio for climbing and 4-limb walking - bipedalism allowed lengthened legs for efficiency and supporting body weight

spine shape and the change that occured

c-shaped spine to s-shaped spine

• bipeds - begun to have s-shaped spines to support bipedalism

for upright walking (balancing the head and torso directly above the pelvis), shock absoption, and keeps the body’s weight centered over the hips and feet (stability)

• quadrapeds - had c-shaped spines to support walking on all fours

forward-leaning posture, less shock absorption (which is also why apes walk with a bent posture when on two legs!)

explain the change that occured in the spine shape 

when bipedalism was discovered early homins began walking upright (on two feet).

around h. erectus, the spine had evolved from ape-like, somewhat curved spines to more prnounced curves that support efficient upright walking and running'

• was optimised for bipedal locomotion and balance

valgus angle and the change that occured

: the inward angle formed between the thigh bone and the vertical axis of the body - also causes knees to point slightly inward.

• bipeds: femur angles inward to bring the knees closer to the center of body 

centers the body’s weight over the feet - improves balance, stability, and efficiency when walking bipedally 

• quadrapeds: minimal or none

capable of bipedal walking but the vertical angle of the femur makes it less efficient. (almost mixed bipedal walking) 

explain the change that occured in the valgus angle

: reflects the shift from tree-climbing and quadrapedal movement to efficient upright walking

• allowed early hominins to walk and run effectively over long distances.

fingers and hands and the change that occured

: function shift from locomotion and climbing to precision grip and tool use

bipeds

• thumb: fully opposable - allows for precision grip and fine motor control 

• fingers: shorter compared to thumb 

quadrapeds

• thumb: less opposable - not specialised for precision grip 

• fingers: long and curved - suitable for grasping branches and climbing (branchaiting) 

explain the change that occured in the fingers and hands

: as hominins began walking upright, their hands were no longer needed for locomotion, allowing them to evolve for manipulation (using them for other purposes)

enabled for:

• crafting tools

• building shelters

• using the thumb and fingers to hold, create, etc.

toes and feet and the change that occured

: transformation from grasping and climbing to weight-bearing structures optimised for walking on two feet 

bipeds

• toes: shorter - improved stride effeciency 

• forward facing toes: distributes weight evenly across the foot, helps propel the body forward with each step

quadrapeds

• toes: longer toes for grasping 

• big toe: divergent and opposable 

explain the change that occured in the toes and feet

: driven by the shift from tree-climbing and brachiating in quadrapedal movement to upright, bipedal walking 

• allowed for walking and running long distances with minimal/gradual energy loss 

• lost climbing agility and foot dexterity, but gained walking efficiency

arch in foot and the change that occured

: longitudinal arch and transverse arch that runs through the foot

• bipeds: significant foot arch

shock absorption, improving balance and stability by acting like a spring to store and release energy during locomotion 

• quadrapeds: flat or minimally

flexibility for grasping and climbing , better contact with brances and surfaces

explain the change that occured in the arch in foot

: allowed early hominins to walk and run long ditances efficiently, supporting endurance, hunting, and migration

• without these arches, the foot would collapse under body weight - leads to instability and fatigue

explain the change in the major potruding skull structures (zygomatic arches, sagittal crest, brow ridge)

large groups of muscles attatch to the jaw and travel thorugh wide zygomatic arches and attatch near the top of the skull to a prominent saggital crest. 

a prominent brow ridge helps disperse the tension forces created by these powerful muscles during masitication.

diastema and the change that occured

: (in apes) the lower canine fits into a gap - the diastema - so that the jaw can close  

• humans: NONE

• apes (quadrapeds): PRESENT

explain the change that occured in the diastema 

: as hominins evolved, canines became smaller. this reduced the need for a diastema to accommodate large lower canines 

• how this happened: diet - softer/processed food 

canine and the change that occured

: pointed sharp teeth located between the incisors and premolars 

• humans: four SMALL (very minimal) canines, cone shaped with pointed tip 

for tearing food, guiding the bite 

• early hominins: LARGE (much much more prominent) 

used for defence, threat display and combat 

(also for eating and ripping food) 

explain the change that occured in the canines

: from physical dominance and raw chewing power to social intelligence, communication and tool use

• shift reflects changes in diet, reduced aggression, and social cooperation 

also resulted in the disappearance of the diastema

prognathism and the change that occured

: snout/muzzle - forward projection of the jaw

• humans: DO NOT show prognathism 

• early hominins: LARGE prominent snout - showing prognathism 

for chewing harder food

explain the change that occured in the prognathism

: prognathism decreased signficantly as a result of a changed diet during human evolution resulting in flatter faces seen in modern humans.

• the need for powerful jaws were reduced as cooking was introduced

• respositioned jaw allowed for better control of the tongue and vocal tract 

dental arcade and the change that occured

: the shape formed by the rows of teeth in the upper and lower jaws 

• humans: bow-shaped (parabolic) 

• early hominins: U- shaped

present to accommodate large canines

explain the change that occured in the dental arcane

: as food became softer - jaw size reduces, tooth arrangement changed

• smaller canines eliminated the need for a distema and allowed for compact dental arch

who hit an evolutionary deadend after h-heidelbergenesis (approx. 300-35kya)? and time frame

h. neanderthalis (125-32 kya)

who are we (current) and from what time frame

h. sapiens (100 kya - present)

who came after a.afarensis and what time frame?

h.habilis (2.5 - 1.5 mya)

• south + east africa

what are the negatives of bipedalism? (there are 5)

1. flat arches

• body isn’t using shock absorption efficiently

• too much weight on only two limbs/feet (instead of four) 

2. too much weight on a small part on the spinal bones compared to quadrapeds which have a more even weight distribution (**)

3. varicose veins 

• as bipedals, our blood collects overtime in vein valves as blood cannot travel efficiently to the heart 

• with quadrapeds: the heart is closer to the feet/hands so they don’t suffer from this problem 

4. hernia 

• bulging intestines 

5. small birth canal (**)

• childbirth in difficult and painful as the pelvis must be tight to hold all intentines and organs inside of our body

what is the early stone age - paleolithic period - relative brain size and what tools were present at this time?

: earliest and longest phase of human prehistory marked by the first use of stone tools by early hominins

tools: oldowan and acheulean 

brain size: 500-650cm (cubed)

what is the late stone age - upper paleolithic period - relative brain size and what tools were present at this time?

: a period of dramatic cultural, technological, and cognitive advancements amoung early hominins 

tools: mousterian (middle) and then to needles, hooks, spears, arrows, etc. (later)

brain size: 750-1250cm (cubed) 

mousterian tools - what, who created them, and time frame

: sophisticated and finely worked scrapers, spear tips and axe heads often mounted on wooden shafts and used as spears or bow and arrow.

• tear-shaped tool

who: h. neanderthals and early h.sapiens

time: approx 1 mya (middle - upper paleolithic)

acheulean tools - what, who created them, and time frame

: broad, flat tools with a straight cutting edge for chopping and butchering - carefully crafter with a slight buldge on each face (called a bi-face)

• A-shaped tool (hard to differentiate between acheulean and mousterian so be careful) 

who: h. erectus and h. heidelbergenesis

• possibly also h. ergaster, and late h. habilis

time: apprx 2 mya 

oldowan tools - what, who created them, and time frame

: very simple, basic stone tools, often called “pebble tools” 

made by striking one stone against another to produce sharp-edged flakes 

who: h.habilis (developers) to h.ergaster

time: approx 2.3 mya 

what was the big change in complexity in cultural evolution (tools) and the change in brain size?

: the shift from simple, generalized stone tools to highly sophisticated tools (around the upper paleolithic time period)

tools like: spears, arrows, blades, etc.

brain size: 1400-1500cm (cubed) 

• larger brains enabled better memory and as knowledge passed down, tools evolved to suit conditions, different climates, resources, etc.

• reflected cultural identity and status.

what are tools such as needles, spears, and arrows classfied as if not entirely mousterian?

: upper paleolithic tool tradition (before the neolithic period - farming, domestication, argiculture)

who: h.neanderthals and early h. sapiens

time: 50,000 years ago

what are the advantages of discovering/developing fire 

1. construction of weapons 

• wooden spear tips could be hardened in fire - sharper and improving their penetratic power 

• rocks heated in a fire became britte - easier to shape into tools (ex. blades and spearheads) - blade also holds a sharper edge

2. hunting tool/predator tool 

• setting fire to forest to drive out food sources 

• used for protection to drive off predators 

3. provides light 

• used as a torch to explore dark places (ex. caves)

• helped with bonding - sitting around the campfire to connect

4. warmth 

5. cooking food

• food was made easier to chew and digest - releasing energy quicker for the body to use

• kills parasites, bacteria, and diseases

• preserve food - meat: smoked - vegetables: dried

how might fire had been discovered and by who

: by h. erectus - may have been “captured” from natural sources

ex. bush fires caused by lightning 

• later, humans developed techiques to create fire on demand 

what are the negatives of fire (there are 3) 

1. predators can see you 

• firelight and smoke can draw attention especially at night 

2. burning yourself

• with minimal understanding - could faace accidental burns or injuries when handling fire 

3. fire could spread 

• damages vegetation, threatening shelter or even killing