Human evolution

Primates

Human classification

Kingdom: Animalia

Phylum: Chordata

Class: Mammals

Order: Primates

Suborder: Anthropoidea

Superfamily: Hominoidea

Family: Hominidae

Genus: Homo

Species: sapiens

Phylum ChordataSub phylum Vertebrata

Animals with a dorsal nerve cord surrounded by bony vertebrae.

Class Mammalia

Mammals suckle their young on milk secreted from mammary glands.

The have hair and sweat glands They are homeothermicThey have a four chambered heart and a

diaphragm They have an external ear (pinna)

More features of mammals

They have four different kinds of teeth – incisors, canines, premolars and molars

They are highly intelligent because they have a larger forebrain than other animals

Three groups of mammals

Monotremes – lay eggs

Marsupials – carry their babies in a pouch for a large part of their development

Placental mammals – nourish their young in a uterus via a placenta

Hominoidea - Superfamily

Hylobatidae (family)(family)

Gibbons

Hominins, hominids and hominoids

• Hominoids – humans, great apes (chimps and gorillas) and lesser apes (gibbons)

• Hominids- humans and great apes

• Hominins - humans and ancestral species

Order Primates

The features of primates are largely related to their arboreal (tree living) way of life.

Brain size• Large and more complex than other mammals.

Collar bone

• Is well developed and the arms have a wide range of movement.

Posture

• More upright, particularly in the upper body. Associated with sitting, standing and in some cases walking.

ReproductionUsually have only one baby at a

time – this baby is born well developed after a relatively long gestation period.

The mammary glands are pectoral (on the chest) so the mothers suckle their young in a sitting position.

Limb joints

Bones of the lower limbs (radius and ulna, tibia and fibula) are not fused.

Primitive skeleton – has undergone less evolutionary change than other animal groups.

Hands and feet

Hands and feet have five digitsGrasping hands, (not claws) with nails -

both fore and hind limbsTips of the fingers have ridges which make

them more sensitive most have opposable thumb

Plantigrade foot posture – whole foot is in contact with the ground

Teeth shape and dental arrangement

• Dental pattern seen in most primates, particularly in the molars. Unspecialised teeth mean primates can adopt a flexible omnivorous diet.

Face shape and snout

Reduced snout.

Olfactory (smell) regions of brain are reduced. Smell is less important in the life of a tree-living animal than vision.

Vision

Forward facing eyes which allow binocular vision – makes it easier to judge distance

Colour vision and ability to see detail.

Social organisation

Live in social groups where the individuals gain protection from predators, food is shared, rearing of young can be shared and individuals can learn from each other.

Page 328 – fill in

APE FEATURES

Features of apes:

• No tail

• Rib cage is flattened

• Molars have 5 cusps (monkeys have 4)

• Locomotion is brachiating, knuckle-walking, or bipedalism.

• Posture partly (or fully) erect… leaving the hands free

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The Y5 molar pattern

Trends in human biological evolution

A trend refers to a change over a period of time

We will look at 3 trends in human biological evolution:

• 1) Trends in changes linked to skull and endocranial features;

• 2) Trends in changes linked to bipedalism

• 3) Trends in changes to the manipulability of the hand.

Differences between ape and human skulls

329 Biozone

Pages 343 and 344

Apes H. sapiens Reason for change

Smaller cranial capacity (~450cc)

Bigger cranium (~1450cc) Increased brain development

Sagittal crestLarge zygomatic archLarge jawTeeth biggerBrow ridge

No Sagittal crestSmall zygomatic archSmall jawTeeth smallerNo brow ridge

More refined diet, no need for really strong chewing muscles, muscle attachment points, or teeth

Nuchal crest No Nuchal crest Head vertical on spine – less muscle attachment needed.

Foramen magnum on angle/back of skull

Foramen magnum central/bottom of skull

Vertical spine with skull on top

No Broca’s and Wernicke’s areas

Broca’s and Wernicke’s areas present

Used for language

Less folding of cerebral cortex Cortex much more folded Related to memory, attention, language, awareness, thought, etc… developed as social structure allows more time, and hands free to carry out abstract tasks

Cerebellum less developed Cerebellum more developed Needed for balance, as well as coordination and tool use

Skull and endocranial changes

Brain size

• The human brain is much larger at 1400 cm3 compared to 450cm3 in apes.

Brain development

• The cerebral cortex is much larger in humans allowing for higher order thinking, speech and language.

• The cerebellum allows for hand eye co-ordination and fine motor skills.

• These are both larger and more developed than apes.

cerebellum

2. In modern humans 2 areas of the brain (cerebral cortex) have become highly developed:

a) Broca’s area – this is concerned with speech. It controls the muscles of the jaw, lips, tongue, soft palate and vocal chords during speech.

a) Wernicke’s area – this is concerned with language of comprehension and the ability to listen.

Page 342

• Look at chimp, human and gorilla skull. Using notes, see if can identify parts.

Brow ridge

• Area of support for large jaw muscles and jaw bone. It is thought that when chewing occurs some stresses can be minimised with the help of the brow ridge

Pelvic inlet

This is the large space in the pelvis.

This is much larger in humans compared to apes and other hominins

This is due to larger brain size of young needed a larger opening during birth

Direct comparison between human and ape skulls

• Read page 263 and 264. Make a table comparing the skull anatomy of humans and apes. Also do ‘teeth’ on page 265.

Trends in skeletal changes linked to bipedalism

• http://www.youtube.com/watch?v=l0tAQcpLILQ&feature=video_response

• http://www.youtube.com/watch?v=IHi3xYS3cOs

• http://www.youtube.com/watch?v=ubEi-dyVDyo

• http://www.youtube.com/watch?v=qPag2gVcRe8

Why did bipedalism evolve ?

Mammals thought to have originated in the Permian age (225-280 million years ago), branching from primitive reptiles.

Survival during time of dinosaurs indicates intelligence and development of keen senses.

Once dinosaurs disappeared, mammals flourished.

• At end of Cretaceous period (63 million years ago) the two supercontinents, Laurasia and Gondwanaland, started breaking up and moving apart.

• In the Palaeocene and Eocene, land masses started to look like they do now. Earliest primates evolved.

• Shifting continents caused great changes in climate. North America and Europe became cooler and plants changed from sub-tropical vegetation to tougher trees and grasses.

Changing climate and bipedalism

Page 360

Advantages of bipedal walking - copy

1) See better over greater distances – advantageous to see predators or prey.

2) Easy harvesting of fruit from small trees

3) Hands free to carry food, tools etc.

4) Can carry babies. – necessary when no longer hairy.

• http://www.youtube.com/watch?v=NAFwd-4CkMM

5) Heat stress in savannas is greater compared with shade of forest. Bipedalism aids in cooling by:

a) reducing amount of sunlight that falls on body – falls on head and shoulders only;

b) increasing exposure to wind and breezes, helping with sweat evaporation. Breezes are faster 2m off the ground than 1m.

6) Standing upright makes wielding a stick or throwing a stone easier, to fend off attackers.

7) Dominance, standing up is more menacing to a would-be attacker.

8) Walking on 2 legs is more energy efficient than walking on 4 legs. BUT running on 4 legs is more efficient than running on 2.

Disadvantages of bipedalism - copy

• S-shaped spine and bowl-shaped pelvis makes humans prone to backache;

• Birth of large headed baby painful;

• Human child takes about a year to walk, crawls first. Four-legged mammals often walking within a few hours of birth.

Adaptations for bipedalism (use for 362 Lucy)

Do page 361 and 362

Page 362 biozone

a) The spine

b) The pelvis and legs

• Pelvis - Humans transmit weight to legs; broader and shorter for greater upper body stability. Apes is narrower and longer; tipped forward.

Humans have larger gluteus maximus to hold femur and pelvis in upright position.

Arms and legs

• Humans Legs are longer than our arms. This allows us to cover more ground per step compared to apes.

Human - Gorilla - Chimpanzee - Orangutan - Gibbon(Note the finger tip level gradation)

c) Feet

Apes and humans have a plantigrade feet- their whole foot is in contact with the ground

d) Knee joint

• Read 266 and 267 textbook

Trends in changes in the manipulative ability of the hand

• Ape fingers are longer and slightly curved. Human fingers are shorter and straight.

• Ape opposable thumb is short and less dexterous. Human opposable thumb is longer and more dexterous

Trends in changes in the manipulative ability of the hand

• The Humans opposable thumb allows for a precision grip. This is because the thumb can be in direct contact with the tips of our fingers. This allows greater control of objects (tool) and to manipulate even small objects.

• In apes, the thumb is short and fingers are long so no precision grip.

Selection for nakedness

Hominid evolution- evolution of humans and pre-humans

A 1960s view of hominid evolution was that evolution progressed in a linear fashion-from a primitive ape-like ancestor to modern humans.

• http://www.youtube.com/watch?v=faRlFsYmkeY

• http://www.youtube.com/watch?v=Lc6U7_-BeGc

BUT Fossil record does not show gradual changes from one species

to next

Now Human Evolution thought of as a succession of adaptive radiations.

• First radiation: early bipedal apes

- Australopithecines evolved

Second radiation: - Paranthropines evolved

Third radiation – Genus Homo evolved

Australopithecines

Paranthropines

This represents one possible

interpretation of the fossil data:

HUMAN ORIGIN Ardipithecus ramedus

Australopithecus anamensis

A. afarensis

A. africanus

Paranthropus robustus P. Boisei

Homo habilis

H. ergaster

H. heidelbergensis

H. neanderthalensisH. sapiens

H. erectus

H. florensiensis

6 m.y.a.

5

4

3

2

1

0.5

Present

The megadonts – vegetarians. a.k.a.

robust A.s

gracile Australopithecines

H. rudolfensis

Manual pg 344/5/7

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Early hominids of Africa

Sahelanthropus tchadensis (toumai)

• Dated at 6-7 mya

• Found in Chad

• might not be bipedal

• ape-like skull and dentition

• Lived in a forest environment

• May be a common ancestor to humans and chimpanzees

• http://www.youtube.com/watch?v=RViD7xiZBjE

Orrorin tugenenesis - claimed to be oldest hominid described. Volcanic rock in area dated to 5-8-6.1 million years ago.

Teeth intermediate between those of chimp and human.

Orrorin tugenenesis – found near village of Tugen, Kenya.

IMPORTANT BIPEDAL FINDSImportant “first” bipedal species finds include:

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Australopithecus africanus

- 1942 (2.5 m.y.a) “Tuang boy”

Australopithecus afarensis

- “Lucy”, 1972

- “The first family”, 1975 (3 m.y.a)

- “Laetoli footprints”, 1977 (3.75 m.y.a)

Ardipithecus ramidus

- 1995 (4.4 m.y.a)

Orrorin tugenensis

- 2001 (6 m.y.a! 1.5 my before thought)

Ardipithicus ramidus

•Ramidus means “root” in the afar language (Ethiopian).

•Fossils found about 4.4 million years old in Ethiopia.

• Teeth part way between apes and Austalopithicus afarensis

• Scientists divided as to whether A. ramidus is an ancestor to chimps or whether an ancestor to australopithicenes.

•Cannot tell if it was bipedal or not.

Key features of Australopithicines

• Australopithecus anamensis, afarensis, and africanus, and Kenyanthropus platyops are collectively known as gracile australopithecines, because of their relatively light, slender build.

• All the gracile species were still more robust than modern H. sapiens.

• Bell shaped cranium• Brain size 380-550cm3

• Large face, no chin• Bipedal• Jaw and teeth moving from being ape-like

to more human-like.• May have spent some time still in the forest

as well as in the open savannah.• Diet probably nuts, fruit and seeds, possibly

scavengers.• Existed 4.2-2mya.

http://images.google.co.nz/imgres?imgurl=http://img23.imageshack.us/img23/8493/090211111005large502529ln6.jpg&imgrefurl=http://chem11.proboards.com/index.cgi%3Fboard%3DUFO%26action%3Dprint%26thread%3D2222&usg=__OIa2QFmPSuByEwApEiVmtXcieSc=&h=418&w=400&sz=25&hl=en&start=1&um=1&tbnid=BoMXSWh2abcRCM:&tbnh=125&tbnw=120&prev=/images%3Fq%3Dbell%2Bshaped%2Bcranium%2Bin%2Bhominids%26hl%3Den%26sa%3DN%26um%3D1

Australopithecus anamensis

• At least 4.2-3.9 mya• Found in Kanapoi, Kenya by Meave Leaky.• Though to be ancestor of A. afarensis.• Evidence suggests living in woodland and open

savannah.• Lower jaw similar to chimps. Leg and ankle

bones similar to A. afarensis, evidence of bipedalism. Upper arm bone very human-like.

Australopithecus anamensis

Laetoli footprints- about 3.8 million years old.

http://www.youtube.com/watch?v=w1Lu4VggDH0

• Footprints showed big toe, ball of foot and arch of foot. Real evidence for bipedalism.

• Two individuals walking closely together.

• Fossils footprints thought to be made by Australopithecus afarensis.

Australopithecus afarensis – the Southern Ape from Afar

• “Lucy” discovered by Don Johanson and his team at Hadar, Ethiopia.

• 40% complete skeleton – 47 bones.

• Dated at 3.2 million years old. Other fossils show A. afarensis around 3.9-2.9 myo.

• Pelvis shape indicated female skeleton.• Short legs indicated 1.1-1.2m tall.• Ape-like face, brow ridges, flat nose and no

chin. Rest of body more human-like.• Bipedal.• Gracile (light, not heavy build).• Sexual dimorphism. Males larger than

females. Other scientists think two different species.

• Brain 375-550cm3.• Smaller canines.

• Teeth are small and unspecialized, indicating a mixed, omnivorous diet of mostly soft foods, such as fruits. The canines, highly developed in existing ape species, are small and undeveloped, in this species, much as in human beings.

• Geographic distribution- East Africa.

• In same area (Afar) the “First Family” uncovered. Fossils of 9 adults and 4 children found.

Australopithecus africanus (southern ape of Africa)

• Thought to have evolved from A. afarensis.

• The partial skull of a six year old child found in Taung, Southern Africa.

• Existed between 3 and 2 mya.

• Less ape-like than A. afarensis

• Large molars, smaller canines (more human-like)

• Foramen magnum at centre of skull - bipedal.

• 1.1-1.4m tall

• Gracile

• Slightly larger brain than A. afarensis ranging from 420-500cm3.

• Diet – fruit and leaves, probably also dug up tuber and roots and may have scavenged meat from dead animals.

Australopithecus garhi

• Discovered in 1997.

• “garhi” means surprise.

• Dated at 2.5 mya.

• There is much controversy about the classification

• Cranial capacity at 450 cm3

The genus Paranthropus

• The paranthropines are thought to have evolved as a side branch (adaptive radiation) from Australopithecus afarensis.

• They were originally clasified as “robust” Australopithicines, ie A. aethiopicus, A robustus and A. boisei. But many scientists think the differences between this branch and the gracile Australopithicines are so great that they should be given there own genus.

Features of paranthropines

• Heavily built, slightly larger that A. africanus.

• Large molars, very heavy jaws, powerful chewing muscles all specialised for eating a bulky, low grade vegetarian diet, probably of roots, shoots and other food.

• Robust skull – large crests for muscle attachment.

• Existed 2.5-1.1mya

Paranthropus robustus

• Existed 2-1.5 mya• Brain size: 530cc3

• Massive flat face with brow ridges, no forehead.

• Bipedal – but long arms and a heavy build.• Huge grinding molars, very large lower

jaw, relatively small incisors and canines. Diet probably tough plant food and roots that require lots of chewing.

• 1.1-1.3m tall• May have used bones as digging tools

Paranthropus boisei

Paranthropus boisei

• Existed 2.1-1.1mya• Brain size: about 530cc3

• 1.1-1.4m tall• Skull – similar to P. robustus but larger face

and larger molars. Diet same as P. robustus.

• Prominent nuchal crest (where neck muscles attach)

• Broad, flat face, large zygomatic arches (cheekbones)

Paranthropus aethiopicus

• Thought of have lived 2.7 – 2.5 mya

• Small brain 410 cc• Thought to be the

direct descendant of A.afarensis because of its similarities.

• Limited other information.

What happened to the Paranthropines?

• Paranthropines co-existed with Australopithicines and early Homo species.

• They were driven to extinction, probably by an intense period of cooling and drying caused by the Ice Age.

• Other species may have been better adapted to changing environment.

There is good fossil evidence that four kinds of hominid lived about 1.8 mya in what is now part of northern Kenya.

They foraged in the same area around Lake Turkana.

We have no idea how, or if, these different species interacted.

Once We Were Not Alone

P. boisei H. habilis H. rudolphensis H. ergaster

Photos courtesy of: SkullsUnlimited.com

General features of the genus Homo

• Changes in shape of the size of the skull, jaws and teeth.

• Increase in brain complexity• Proportional lengthening of legs in relation

to arms and trunk• Development of speech• Development of tools• Gradual development of group living and

culture

Key features of Homo habilis

• First member of the Homo line.

• Existed between 2.4-1.5mya.

• Brain size larger than Australopithicines: 500-800cc3 . This is still only half of H. sapiens.

• Habilis = handyman. Thought to be the first to make and

use tools. Tools indicate partly carnivorous diet. Teeth indicate omnivorous. Small jaws with small incisors and canines and small molars (but larger than H. sapiens).

• Evidence of co-operative hunting and scavenging for food.

• Height: 1-1.3m.

• Some sexual dimorphism but less than Australopithicines.

• Skull – rounded human shape but with brow ridges.

• As H. habilis evolved about 2.5 mya when world’s weather system undergoing great changes. Bouts of warming and cooling occurred every few thousand years. Ocean currents shifted and realigned, sometimes in less than a decade.

• Resulted in lower temperatures and less rainfall. Forests in Africa dried up, animal populations began to crash. Human ancestors, ie all those prior to H. habilis, lived through many cycles of climate change but each caused population bottlenecks, so many relatives eliminated.

• H. habilis thought to have made tools. By making tools could skin carcasses and crack open the bones for the marrow. Could also use tools to break down veges and nuts.

• Australopithicines responded to climate change by walking upright. The first members of the Homo line responded to climate change by developing tools and eating a more varied diet.

Tools = Oldawan tools

• Reading 274-278 textbook

Key features of Homo ergaster

• Existed 1.9-1.7 mya. Previously classified as H.erectus.

• Brain 850-1000cc3

• Body shape similar to modern humans• Higher domed cranium and thinner skull

than H.erectus.• Small front teeth and smaller molars than

H.habilis – omnivores.

• Thought to have travelled out of Africa to Asia.

• 1.3-1.85m tall.

• Nose projected more

• May have been capable of speech

• No sexual dimorphism, suggests males didn’t fight for females.

9 years old and 1.6m tall

Key features of Homo erectus

• Migrated extensively from Africa to Asia and Europe.

• Developed acheulian tools – cleavers, picks and handaxes. More advanced tools show H.erectus could plan with forethought.

• Brain = 750-1250cm3

• Projecting nose. Prominent brow ridges, thicker skull bones.

Acheulian tools

• 1.3-1.7m tall. • Similar build to modern humans but

sturdier arms and leg bones• Used fire. Charred bones and stones have

been found with fossils in may sites, indicated cooked food.

• May have hunted and trapped animals. Had a much more diverse diet due to eating animals. This meant less energy spent digesting low nutrient containing vegetation.

• Infants would get higher quality food for their brains. Therefore brains get bigger, could think of better ways to get meat and the cycle continues.

• H. erectus first to have barrel-shaped ribcage. Makes way for lungs AND means a smaller gut area.

• Worlds oldest house, found in Japan, dated 0.5mya attributed to H.erectus.

Homo floresiensis

Discovered in 2003 on the

Indonesian island of Flores,

nicknamed ‘the hobbit’, these

hominids lived 95 000 - 13 000

years ago.

The dimensions of the skull and

skeleton of H. floresiensis fall well

outside the extremes seen in H. sapiens.

It is equal to the smallest known

australopithecines, and approaches that

of modern chimpanzees (which have a

brain size of 400cc).H. floresiensis skull shown next to a modern human skull to show its size.

Timor

Flores

Java

Sulawesi

Borneo

Sumatra

New Guinea

Photo courtesy of: SkullsUnlimited.com

Homo floresiensis

Fossils from a number of individuals include a

30 year old female with a brain size of 380cc

and standing just 1.0m tall.

May have resulted from long-term

isolation, with subsequent endemic

dwarfing, of an ancestral Homo erectus

population (dwarf forms of large mainland

mammal species are not uncommon on

islands).

Astounded scientists by showing clear

signs that (despite their very small brain

size) they used stone tools and fire, and

hunted dwarf elephants, also found on the

island.

H. floresiensis may have been part of

the Asian dispersals of the

descendants of H. ergaster and H.

erectus.Photo courtesy of: SkullsUnlimited.com

Key features of archaic H.sapiens = H.heidelbergensis

• Existed 400,000 to 100 000 years ago in Africa, Asia and Europe.

• 1.5m tall• Robust but human-like skeleton• A lot of variation in fossils dated to this

time. May indicate populations responding to diverse regional selection pressures.

• Brain size: 1100 to 1400cc3.

• More prominent nose

• Changes in voice box position may indicate speech.

• May have evolved into H.sapiens and/or H. neanderthalensis.

Key features of Homo neanderthalensis

• Existed 230,000-28,000 years ago• Brain size 1200-1750 (larger than modern

humans, but they were also bigger overall)• 1.5-1.7m tall• More sloping forehead than H.sapiens.

“Bun” at back of head where strong neck muscles attached.

• Brow ridges, receding chin.

• Had thicker bones than H. sapiens, for attachment of large muscles.

• Lived in very cold conditions. Thicker limbs and stocky shape were adaptations to the cold and still found in modern human populations in cold climates.

• Used Mousterian tools – more advanced than Achaulean tools. Some attached to handles.

• Buried their dead with things such as food, flowers, tools or jewellery. Suggests may have thought about afterlife, or they mourned their dead.

• Used fire for cooking, warmth and to scare off predators.

• Sometimes lived in caves and built stone walls and curtains of skin to keep out wind. Also made tents and clothes.

• Probably had some form of language as they had the required throat structure to allow speech.

• Originally thought H. neanderthalensis evolved into H. sapiens, but mt DNA analysis between the two shows large number of differences. Suggests H. sapiens originated in Africa, migrated to Europe where they replaced H. neanderthalensis with little or no interbreeding.

BUT have found a skeleton with DNA features of both human and neanderthal DNA. Suggests may have interbred.

Key features of Homo sapiens• Cranial volume 1200-1700cm3.• Earliest H. sapiens fossils from Africa about

160,000 years ago.

• Then spread to Asia, Europe, Australia and America. Reached Europe about 35,000 years ago.

• In Europe co-existed with H. neanderthalensis but then H. neanderthalensis died out about 25, 000 years ago.

• More gracile than neanderthals, probably because evolved in a hot climate.

• Skull has no brow ridges, a high forehead, well-developed chin, long nose, small teeth in a v-shaped jaw.

• With appearance of Cro-Magnon man (35 000 years ago) a cultural revolution was caused. Cro-Magnon man was artistic, made more sophisticated tools including fish hooks, needles and harpoons.

Buried their dead.