Hominin Evolution Humans share - PowerPoint Presentation

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Hominin

Evolution

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Humans share

an extinct

common ancestor with primates

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Primate featuresOpposable thumbs – thumbs can touch fingers. This allows for grasping objects and climbingLarge forward-facing eyes and flattened face to allow for stereoscopic (3D) vision (overlapping fields of vision)

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Supra-orbital ridge (protective bony ridge at top of eye socket)Brachiation – shoulder is flexible due to ball and socket joint and can rotate arm behind body (good to swing between branches)

Primate features

Brachiation

in gibbons (a type of primate)

Supraorbital ridge

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Large cranial capacity (brain case) compared to body size

Primate features

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Hominid (Hominoid) – the group consisting of all modern and extinct Great Apes (that is, modern humans, chimpanzees, gorillas and orang-utans plus all their immediate ancestors).Hominin – the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).

Terms……

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Hominin

Cladogram

Note: Chimpanzees are not part of the

Hominins

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Bipedalism distinguishes hominins from the other primatesAdvantages of bipedalism (learn these!)Leaves hands free to carry and make items (cultural evolution), hunt and forageAble to see over rocks and other obstaclesCan regulate body temperature better (less surface area exposed to the sun)Utilises less energy to get around….extra energy can be used by the brain (belief that increased cranial capacity in hominins is linked to bipedalism)Fossil evidence shows that upright posture occurred before increases in cranial capacity (brain size)

Bipedalism (walking upright on 2 legs)

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Bipedalism and thermoregulation

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Position of foramen magnum (hole in skull where the vertebrae join it) is more central

Evidence of bipedalism in fossils

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Evidence of bipedalism in fossils

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S-shaped spine helps support weight and maintain centre of gravityShorter, wider pelvis indicates that the muscles attached to it are at such an angle that they are involved in walking upright with gravity centred through the middle of the organismFemur angled inwards ensures weight is kept central and directed towards the knees.

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Evidence of bipedalism

Forward facing big toe – centres weight

Non-

hominin

primates have their larger digit pointing outwards – good for grasping branches

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Before the genus Homo there was Australopithecus

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Australopithecus

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A robust body is heavy in skeletal structure and muscle (cannot move fast)A gracile body is lighter and more slender (faster)Fossil evidence suggests that the robust Australopithecines line became extinct.Therefore modern human ancestors (the Homo genus) came from the gracile Australopithecus lineage.

Our ancestors come from

Gracile

Australopithecus

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The genus Homo

Reduced canines from chimpanzee to genus HomoMore parabolic (curved) jaw shapeLoss of gap (diastema) between canines and premolarsLess molarsSuggests lesstough fibre andless reliance onmeat in genusHomo

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Larger cranial capacity (don’t write “larger brain size” as the brain is no longer present to directly observe)

The genus Homo

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With an increase in cranial capacity, more nerves needed to travel between the brain and the bodyThe hole in the centre of the vertebrae increased in size from Australopithecus to Homo, allowing extra space for the extra nerves (this feature was selected for)

The genus Homo

Central canal

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Flatter faces and use of tools (cultural evolution) in genus Homo

The genus Homo

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Transitional fossils between Australopithecus and Homo genus

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Zygomatic

arch and sagittal crest is smaller in genus Homo

Zygomatic

arch in a herbivore is larger to accommodate more jaw muscles for more chewing

Sagittal crest

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The sagittal crest is an attachment point for muscles involved in chewing. If it is larger, there is more

fiber in the organism’s diet.

Sagittal crest

Zygomatic arch

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Order the following from closest human to least closest human ancestor

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Phylogenic

Tree of Human Ancestors

First to use tools

First to use fire and leave Africa

Able to walk upright

Robust (not

gracile

)

Not a direct ancestor of modern humans

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Two theories:Multiregional hypothesis -modern humans evolved from different tribes of Homo erectus and evolved separately 2) Replacement hypothesis (Out of Africa hypothesis) -modern humans came from one tribe of Homo erectus and replaced all other tribes. -Neanderthals, therefore, were evolutionary dead ends

Separate species or interbreeding?

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Fossil evidence (transitional forms mostly found in Africa)Mitochondrial DNA (mtDNA variation is greater in African populations compared to other worldwide populations. Shows that African populations have been around longer and therefore more time for more accumulations in mutations to occur).Y chromosome DNA variations (as per mtDNA but inherited paternally)

Out of Africa Hypothesis is supported by more evidence

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mtDNA

haplogroups and Out of Africa Theory

Oldest

haplogroup

is L, followed by M

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Different regions have different selection pressuresThis results in different traits being selected for (e.g amount of pigmentation in skin)

Why do we all look different?

Skin pigmentation correlates with latitude because it serves as a

defense

against UV radiation.

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Learned behaviours transmitted throughout generations (development of customs and languages)e.g. music, art, pottery, writing, jewellery

Cultural Evolution

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Changes in technology which give humans more control over their environmente.g. development of tools, agriculture, medicine, space travel, communication devices

Technological Evolution