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Evolution - Coggle Diagram
Evolution
Dispersal of Hominins
H. erectus was the first hominin to leave Africa
Migration from Africa was possibly linked to climate change in Africa that resulted in a cooler, drier climate with open savannah and subsequent reduction in food supplies.
Dispersal began early in their evolution and occurred rapidly - it took only about 200,000 years for H. erectus to appear is Asia and about 300,000 years for the species to appear in Europe
Out Of Africa Theory
Archaic H. sapiens evolved into anatomically modern H. sapiens solely in Africa (between 200,000 and 150,000 ya)
The highest level of genetic variation in mt DNA in humans occurs in African populations - implies modern humans arose in Africa so have had a longer time for the accumulation of genetic differences
The first dispersal of H. sapiens from Africa occurred possibly as early as 130,000 ya, with a second wave of dispersal occurring sometime between 70,000 and 40,000 ya.
The earliest successful migration (ie, those who left living descendants) is widely accepted as occurring 60,000 ya
Migrants of the second wave replaced earlier human populations - such as H. erectus, H. neanderthalensis - in Europe and Asia
It is considered that the recent single origin of modern humans was in East Africa (Rift Valley location)
There are few differences in the DNA (genotype) of H. sapiens, geographic variations in physical appearance (phenotype) seen in modern-day humans resulted from natural selection, sexual selection and genetic drift
Genetic drift is a mechanism of evolution. It refers to random fluctuations in the frequencies of alleles from generation to generation due to chance events. Genetic drift can cause traits to be dominant or disappear from a population. The effects of genetic drift are most pronounced in small populations.
Founder and Bottleneck effect.
The low level of genetic diversity in present-day humans suggests a relatively small population of only 10,000 to 50,000 left Africa sometime between 125,000 and 50,000 ya; this population (or populations) may also have been subjected to the bottleneck effect during migration.
The further away from Africa, the less genetic diversity in modern human populations.
Multiregional Theory
Says that after H. erectus left Africa and dispersed, regional populations of them slowly evolved into modern human,
Regional, geographically isolated populations adapted to their environment through natural selection.
Gene flow existed between adjacent populations ad this mixing of alleles prevented speciation (no reproductive isolation).
Therefore, all modern humans are descended from H. erectus who left Africa about 2 mya; there has been a single, continuous, human species since then
Fossils have been found in Asia that show an intermediate between H. erectus and H. sapiens
DNA sequencing
Analysis from both nuclear and mtDNA allowed comparisons to be made between genomes of different species/populations. The fewer the differences, the more closely related the populations/species.
mtDNA analysis
Mitochondria are present in the ovum, not the sperm - they are therefore inherited through the maternal line. Mitochondria is not subject to natural selection or independent assortment, therefore changes in sequence result from random mutation only. These mutations tend to occur at a steady and comparatively rapid rate, so can be used as a 'molecular clock' for tracing ancestry, determining relationships and compiling phylogenetic trees.
Y-chromesome DNA
The Y-chromosome is a short chromosome with only a few genes and is not as prone to crossing over as other larger chromosomes. As only sperm contain the Y-chromesome, it is inherited through the paternal line. Therefore, as the Y-chromesome is inherited largely unchanged over generations, it can also be useful tool in tracing ancestry and determining relationships.
Biological Evolution
Biological evolution results from the transmission of genetic material from generation to generation.
Biological evolution is random and tends to be slow, with the rate determined by mutation, natural selection and environmental change.
Mutations occur by chance; they do not occur in response to a need.
Trends In Biological Evolution
Changes in the skull and endocranial features
Skull
Changes in diet including the impact of controlling fire and being able to cook food increased the size and complexity of the brain
high forehead
large cranium
no brow ridge
Changes in diet as cooked food became more common (tenderised meat, easier to chew)
small canine
reduced zygomatic arch
reduction in sagittal crest
short, circular/parabolic jaw
flat face, no prognathism
prominent chin
Brain
Increase in size and volume
Increase in complexity and specialisation of the brain, especially the cerebrum - the outer layer of this (the cerebral cortex) is folded extensively in modern humans
associated with reasoning, problem solving, abstract thought and communication
Broca's area (associated with the organisation of sounds into speech)
Wernicke's area (associated with the interpretation of speech)
Improvements in brain size and complexity and functioning are related to improvements in diet - both the quantity and quality of food. The change in brain size, complexity and therefore functioning only became possible when our diet changed to provide more fat and protein.
Positive feedback loop between biological evolution and cultural evolution.
Changes in the manipulative ability of the hand
Bipedalism meant the freeing of the hand, which allowed for the evolution of of specialised grasping hand with its precision grip.
Precision grip really important for the development, manufacture and use of tools
Key adaptation is the fully opposable thumb that is relatively longer than that of apes and early hominids
Flexible structure of the wrist allows for the thumb to be brought across the hand so it can touch the tip of every finger.
All primates have a power grip, but only humans have a precision grip
The hands lost the distinctive curve seen in apes and early hominins, and which is an adaptation to brachiation.
Skeletal changes linked to bipedalism
Defining characteristic of hominins, and it is likely to be the driving force for subsequent hominid evolution.
Developed at least 4.2 mya, possibly as early as 6 mya
Bipedalism evolved before the expansion of the cranium/brain
two-legged bipedal stance is much less stable / more prone to tripping the the four-legged quadrupedal stance, therefore, any chances in skeletal structure that maintain the centre of gravity inside the body enable dance and will be selected for
A body is balanced when the centre or gravity falls within the base of support. Quadrupedal organisms have a wide base of support; bipedal organisms have a much narrower base of support
Centralisation of the foramen magnum under the skull.
Allowing the skull to balance on top of the skull
reduction in the nuchal crest (site of attachment of the neck muscles) as there is a reduced need to support the head
Spine s-shaped
to act as a shock absorber and keep body weight / centre of gravity above the hips
rib cage is flattened from back to front
allowing the centre of gravity to be close to the spine
pelvis is short and wide (bowl-shaped)
reducing the stress of the upper body weight on the hips and to support the internal organs
the strong bones of the pelvis support the late muscles associated with walking
the wide pelvis also allows Abbies to be born with comparatively wide skulls
femur is long, with a pronounced valgus angle
results in the femur angling in towards the knees, which are brought under the body so that the body weight is centred though the middle of the pelvis when walking
the knee end of the femur has buttresses of bone (lateral formal condyle), which atto prevent sideways slippage when walking, increasing stability
feet are arched
Acts as a shock absorber
toes are aligned forward
the foot pivots over the big toe at the end of each step
The most important advantage of bipedalism is that it freed the hands to carry out a variety of functions.
Carrying food/tools/weapons/babies
Gathering food
wielding weapons
(subsequently) manufacture and use of tools
Miscellaneous Advantages
greater height
individuals could look over grass
appeared more imtimidating
bipedal movement is more efficient that quadrupedal movement
increased ability to keep cool as air flow around body increases
Disadvantages of bipedalism
giving birth, as the large brained baby has to pass through the narrow pelvis during birth (this resulted in high infant and maternal mortality prior to modern medicine)
more stress on lower back, hips, knees and feet
About 5 mya, the African climate changed, becoming cooler and drier, with dense forest giving way to open savannah (grasslands with scattered trees experiencing seasonally dry, hot seasons).
Cultural Evolution
Results from the transmission of learning/knowledge between and within generations.
Knowledge (eg, ideas, beliefs, customs and values) results from higher-level thinking and is stored as memory as well as in written form, and is transmitted by language (both spoken and written).
Cultural evolution is directional and tends to be rapid.
Trends in cultural evolution
manufacture and use of tools (stone/bone/wood)
Oldowan
H. habilis
2.6 - 1.7 mya
Made from river stones by striking flakes off to produce a cutting edge, these tools were probably used as choppers and hammers to crack bones for marrow, to cut and soften meat and to cut plant material and wood
Acheulean
H. erectus and archaic H. sapiens
1.5 mya - 150,000 ya
The flattened hand axe was produced by striking multiple flakes off a central core, resulting in a bifacial tool with a characteristic teardrop, oval, or disc shape. It is likely these were multi-purpose tools for cutting carcasses, scraping/cutting hides or cutting/breaking wood.
Mousterian
H. neanderthalensis
200,000 - 30,000 ya
These tools were more varied and sophisticated than Acheulean tools, with over 60 different kinds identified. Made from flakes that had been struck from a core (rather than using the core itself), they were used as blades, points chisels, scrapers and spear tips (attached to wooden handles)
Upper Palaeolithic
H. sapiens
40,000 ya to now
bone, antlers, ivory, wood, leather, sinew, handles, composite tools
Perforation resulted in the manufacture of needles and fish hooks
controlled use of fire
H. erectus
Evidence from hearths
Rings of stone
Presence of charcoal
Heat-altered sontes
Charred bones of animals
Advantages of fire
Keeping predators away
Providing light, which 'extended' daylight hours
providing a warm meeting place, thus enhancing all aspects of social interaction
source of warmth, allowing new locations with new resources to be inhabited
Improved hunting success as a result of using fire-hardened spear points, as well as using fire to drive animals into traps / over cliffs
Cooking food
Cooking makes food softer and therefore easier to chew and digest, releasing more nutrients.
Improves food hygiene by killing parasites and detoxifying some plant poisons
Improved diet led to improved health and survival and increased the supply of nutrients, which were essential for the development of a large, complex brain.
The significant changes in diet (eg, increased amounts of proteins and fat) that resulted from co-operative hunting, together with evolution and the controlled use of fire, all greatly facilitated brain development. The brain increasingly became an organ of learning adapted for survival, with the mental functions of thinking, learning and memory. A positive feedback loop between biological and cultural evolution was occurring.
ability to make clothes and shelters
communication, especially language / abstract communication / art
Over time communication became more effective, resulting in a great improvement in the ability to plan and co-ordinate activities
Early humans could much more effectively work together, co-operating in activities such as hunting, gathering food, designing and manufacturing stone tools, building dwellings, sharing ideas and making decisions, and establishing and maintaining complex societies.
Art and aesthetics became possible - eg, cave painting, body ornaments and figurines, ritual burial of the dead. Art enriched the environment. It acted to bind members of a community together, thus enhancing survival. Also used for instructional purposes.
food gathering - hunter-gathering / co-operate hunting
Early hominins led a hunter-gatherer lifestyle
They were nomadic
12,000 - 10,000 ya H. sapiens made the transition from being nomadic hunter-gatherers to become settled farmers.
They began to build permanent dwellings, cultivate crops and domesticate farm animals
They realised they could control the breeding and growth of certain plants and animals - selective breeding
Advantages
More dependable source of food throughout the year, with surplus stored or traded (for needed resources)
Improved health, survival, life expectancy (which had a flow-on effect to cultural evolution - eg, more opportunities to pass on knowledge to younger people)
Time spent on food gathering was greatly reduced, which allowed for specialisation and downtime for thought, reflection, socialisation, art, planning, development of tool technology, etc.
Supply of hides and wool increases, resulting in increased production of clothing, containers, tools and housing.
Animals - horses, cattle - could be used for transport, facilitating movement of people and goods.
The advantages of the settled lifestyle over time outweighed the disadvantages, resulting in it gradually replacing the hunter-gatherer lifestyle (now only found in certain areas of the world).
Disadvantages
Increased density of both plants and animals resulted in greatly increased incidence and spread of disease
Increased density of people resulted in increased spread of disease throughout populations, especially those diseases resulting from poor sanitation
Increase in pests and parasites
The seasonal supple of food required monitoring of supply and careful storage.
The annual crop was dependent on favourable weather conditions
As settlements were fixed, catastrophic environmental events could wipe out the settlement and its crops/animals/stores.
domestication and farming of animals and plants, with development of permanent settlements
Primates
Hominids (great apes and humans)
Hominins (a subfamily of hominids that includes all living and fossil species belonging to the human lineage)
Ardipithecus and Australopithecus
Ardipithecus ramidus
4.5 mya in East Africa
About 1.2 m tall, weighing 50 kg
350 cm^3 brain
Foramen magnum relatively far forward, indicating bipedalism
Relatively long arm bone, curved hands and grasping big toe all indicate an arboreal existence.
Australopithecus anamensis
A. afarensis (Lucy)
4-3 mya in East Africa
1 m (females), 1.5 m (males), indicating sexual dimorphism
385-450 cm^3 brain
Valgus angle, indicating bipedalism
A. africanus
A. robustus
A. boisei
evolutionary dead end
Earliest known pre-humans, with a fossil record dating from about 4.4 mya to about 1.2 mya.
All australopithecine fossils have been found in Eastern or Southern Africa
Bipedal
Small brains (350-600cm^3)
Small stature (1.2-1.5m, 30-50kg)
Sexually dimorphic
Reduced canines, not protruding.
Homo
Homo habilis
2.4-1.4 mya
Body form similar to australopithecines; 1.3 m; 37 kg
600cm^3 brain
Hunter-gatherer
Oldowan tools
H. erectus
1.8 mya - 300,000 ya
First to leave Africa, dispersing through Asia and Europe
1.8 m, 68 kg
750 to 1250 cm^3, average about 930 cm^3
Large brow ridges
Evidence of Broca's area in skull indicates language ability.
Hunter-gatherers
Acheulean tools
First evidence of controlled use of fire.
H. floresiensis
H. luzonensis
H. naledi
H. heidelbergensis
700,000 - 200,000 ya
Up to 1.8 m
100 kg +
Broca's and Wernicke's areas indicate language ability.
Dispersed into Europe by 600,000 ya
Evolved into H. neanderthalensis by 300,000 ya
Acheulean tools
H. neanderthalensis
200,000 - 30,000 ya
Shorter and stockier
1.64-1.68 m (males), 1.52-1.56 m (females)
Robust skull with prominent brow ridges
1500^3 brain
Presence of Broca's area and the FOXP2 gene (associated with the development of language and speech) indicate language ability.
Mousterian tools
Cave-dwelling (and there is evidence that they built shelters)
Hunter-gatherers
Cave art
Cared for injured/aged
Burial of dead
DNA analysis indicated interbreeding with H. sapiens
Outcompeted by H. sapiens
H. sapiens
Evolved from H. heidelbergensis about 200,000 ya in Africa and then dispersed throughout the world
1.5 - 1.8 m, gracile skeleton
Hands display precision grip
Flat face with prominent chin, high vertical forehead, small brow ridges
Teeth small and uniform
1350 to 1450 cm^3 brain
Upper Palaeolithic tools
Sophisticated language
Complex societies
Trends over the Homo genus
Average height and weight increased
Brain progressively became larger and more complex, with the cranium becoming larger and more rounded
Development of Broca's and Wernicke's Area
Face became flatter
Forehead became steeper
Jaws and teeth size reduced
reduction in brow ridges
limb bones becoming increasingly gracile with legs becoming longer than arms, became completely bipedal