Human Evolution

Part I

Who are we?

• Homo sapiens is one approximately 230 living primate species, which together constitute the order Primates.

• We, as primates, have inherited a set of anatomical and behavioural features that reflect our evolutionary history.

• By studying the characteristics of present-day primates, we are able to look back at stages in our own evolutionary development.

What is a primate?• Most primates are tree-dwellers and are found in tropical

forest and woodland habitats. • As well as living species, primates also include extinct

species such as Homo erectus and various species of Australopithecus and Paranthropus.

• Living primates include:– Prosimians — these include lemurs, lorises and tarsiers– New World monkeys from South and Central America — these

include capuchin monkeys (Cebus spp.) and spider monkeys (Ateles spp.)

– Old World monkeys from Africa and Asia — these include baboons (Papio spp.) and macaque monkeys (Macaca spp.)

– Apes — these include gibbons (Hylobates spp.) of south-east Asia, orang-utans (Pongo pygmaeus) of Borneo and Sumatra, gorillas (Gorilla spp.), chimps (Pan spp.) of Africa and humans (Homo sapiens).

Characteristics of Primates• No single feature is diagnostic of

a primate but, taken together, the following features identify a primate.

• Hands and feet of a primate typically have:– five digits that can grasp or curl

around objects and primate thumbs or big toes (sometimes both) are opposable, that is, they are able to be brought into contact with the other digits, flat nails on their digits with the tips of their digits able to gain information thorough the sense of touch.

• Primates have an emphasis on vision and they have:– large forward-facing eyes that give

stereoscopic (3-D) vision– colour vision because they have

cones in the retinas of their eyes– a protective bone at the outer side

of the eye socket

Characteristics of Primates

• Primate skeletons have flexibility adapted to life in the trees, such as the ability to rotate the arm in the shoulder socket so that the arm can extend behind the body.

• Compared with other mammals, primates have large brains relative to their body sizes — we primates are more brains than brawn!

• Primates are social mammals and typically live in groups that, depending on the species, may be as large as a troop of several hundred animals or as small as a pair

• Primates have a relatively long gestation period compared with non-primate mammals. They typically produce just a single young at each birth and provide parental care for an extended period that is longest in the case of human children. This longer gestation period allows for the more extensive fetal brain growth of primates.

Primate Classification

Humans are hominoids

• Among the primates, humans are hominoids or members of the superfamily Hominoidea.

• Humans share membership of the superfamily Hominoidea with the lesser apes or gibbons and the other great apes (chimps, gorillas, orang-utans).

• All the apes are hominoids.• Anatomical features common to all Hominoids:

– No tail– Semi-erect or fully erect posture– Broad chest, pelvis and shoulders– Relatively long arms and mobile shoulder joints– Larger brain

Humans are hominins• Modern classification places humans in the taxonomic

group known as tribe Hominini, that is, humans are hominins.

• It is only at this level of classification that humans are separated from all the other great apes. Based on this classification, members of the genus Homo (humans) and their extinct erect-walking ancestors are now strictly termed hominins.

• Anatomical features and habits of hominins (previously called hominids) are:– Bipedal – modified feet, thigh bone, pelvis, spine– Large cerebral cortex (forebrain)– Reduced canines (and teeth in general)– Nose and chin are prominent, reduced eye ridges– Highly sensitive skin– Body hair short or very reduced to assist cooling– Complex social behaviour

Terminology:hominin versus hominid

The most recent definitions are: • Hominid - 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).

Previous definitions:• Current use of the term 'hominid' can be confusing because the definition

of this word has changed over time. • The term 'hominid' used to have the same meaning that 'hominin' now

has. It was therefore a very useful term to designate the line leading to modern humans and was used when referring to various members of our human evolutionary tree.

• The problem for students and teachers is that a lot of texts still use the old system and many Internet sites also haven't caught up, even those of many reputable scientific establishments. So students/teachers will need to be aware that 'hominids' can mean two different things depending on how up-to-date a reference is with regard to incorporating these taxonomy/classification changes.

Evolution of primates• The times of divergence of various primate groups from a

common ancestor have been inferred by comparing the groups in terms of their structure and shape (morphology) or in terms of the composition of particular proteins that they share (biochemical analysis) or in terms of DNA sequences.

• An early divergence about 65 Myr ago produced one line that led to the primates that are represented today by lemurs, lorises and the aye-aye, which form a group known as prosimians.

• About 40 Myr ago, another divergence produced two lines, one leading to the New World monkeys and the second giving rise to the Old World monkeys and apes.

• The latter line subsequently diverged, perhaps about 31 Myr ago, to produce the Old World monkey line and the ape line.

• When the morphology and blood protein composition of the various apes are compared, it may be concluded that the gibbon line diverged, probably 18 Myr ago, and the orang-utan (Asian ape) line, possibly 14 Myr ago.

• Finally, the evolutionary line that led to humans diverged from the line that was ancestral to the African apes (chimpanzees and gorillas).

Evolution of primates• When scientists talk about the ‘human’ line

diverging from the African ape line, this does not mean that humans evolved from chimpanzees or gorillas.

• It means that at some time in the past the ‘human’ line and the African ape line shared a common ancestor.

• This common ancestor gave rise to two lines that evolved along different pathways, occupied different habitats and were subject to different selection pressures.

• The ‘human’ line evolved over millions of years and is represented today by the human species, while the ‘African ape’ line over the same period evolved and is represented today by three species — chimpanzees (2) and gorillas.

When did the ‘human’ line diverge?

• The answer to this question can only be inferred. • Using the ‘molecular clock’ approach in the late 1960s, two American

biochemists, Vincent Sarich and Allan Wilson, estimated that the hominin line diverged from the African ape line probably about six million years ago.

• This view was initially strongly opposed by several palaeoanthropologists who held the view that the line that finally led to humans diverged from the ape line 30 or more million years ago.

• Later fossil discoveries supported the date of divergence proposed by Sarich and Wilson as did comparisons of the DNA sequences of the living apes.

• The incomplete nature of the fossil record is incomplete and various palaeoanthropologists put different interpretations on this evidence.

• Consequently, there is not universal agreement on the precise evolutionary history of the human species.

• There is agreement that small-brained hominins separated from the line that led to the gorillas and chimpanzees, and that these hominins gradually became less ape-like and more human-like as generations of hominins spent more time at ground level and were subjected to various selection pressures.

• Finally, the hominins reached a stage where they were identifiably human and could be classified as members of genus Homo.

Evolution of primates

Human characteristicscompared to other primates

• Brains became enlarged• High forehead, head held vertically• Reduced neck muscles• Teeth covered with thick enamel, reduced molars, small

canines• Shortened forelimbs• Fully opposable thumb• Reduced lower back with S-shaped curvature• Short, wide pelvis for attachment of gluteal muscles for

walking• Femoral head angled and strengthened• Leg bones are thickened and longer• Buttress at knee-joint to allow bipedal walking• Foot has an arch with weight-bearing heel and ball• Non-opposable and forward thrusting big toe• Reduction in body hair to increase evaporative cooling

Selection for Bipedalism• Seeing over the grass may have helped spot predators or

locate carcasses at a distance• Carrying food away from a kill site or growing site to a

position of safety• Efficient locomotion: bipedalism provides an energy

efficient method that favours low speed, long distance movement - walking

• Thermoregulation: two major advantages of walking are:– Smaller surface area presented to sun at midday (60% less)– Greater air flow across the body when it is lifted higher off the

ground assists cooling

• Carrying offspring while following the large game herds of the savannah on long seasonal migrations

• Holding tools and weapons was probably a consequence of bipedalism, rather than a cause

Selection for NakednessRetention of head hair• Hair on the head (and to a lesser extent the shoulders)

reflects and radiates solar radiation (heat) before it reaches the skin

Parasite control• Reduced body hair improves control of ectoparasites such

as fleas, ticks and lice.• Particularly important when early hominins began to use a

regular ‘home base’’ as hatching parasite eggs could reinfect them

Thermoregulation• Shorter, finer hairs (not hair loss) in early hominins has

allowed greater heat loss by radiating from the skin surface• Well developed sweat glands allow us to lose heat at an

astounding 700watss/m2 of skin (a capacity not approached by any other mammal)

Adaptations for BipedalismPosition of Foramen Magnum• Located more centrally under the skull, so that the skull is balanced on the

spine

Spine Shape• Lower back is reduced to produce and ‘S’ shape that has the effect of keeping

the head and torso above the centre of gravity

Pelvis Shape• Short and broad, for attachment of large, powerful muscles for walking• Pelvis has become more ‘bowl-shaped’ to provide support for the organs of the

torso

Femur• Longer and angled inwards from the hips so knees nearly touch (the ‘carrying

angle’) – assists the upper body to be positioned over the centre of gravity

Knee joint• Bottom of the femur (knee joint) has a buttress of bone (called the lateral

condyle) – this stops the sideways deflection of thigh muscles during walking

Shape of Foot• The anatomy of the foot has changed to become a platform.• Toes are short, with big toe forward thrusting.• Inner side of the foot is elevated into an arch to provide a shock absorber

effect.

Changes in the Skull Base• An important diagnostic feature of whether a prospective hominin

fossil skull belonged to a bipedal individual is the position of the foramen magnum on the base of the skull

• The foramen magnum is the attachment point for the skull and the spine through which the spinal cord passes to the brain

• An opening at the rear of the skull implies a quadrupedal habit of locomotion – the head is held upright by powerful neck muscles

• An opening located more centrally on the skull, as is found in modern humans, indicates a bipedal habit of locomotion – the head balances on the spine, requiring less powerful neck muscles

1960s View of Human Evolution

• Belief in linear progression from primitive ape-like ancestor to modern humans

• According to this model, the fossil record should consistently show smooth inter-gradations from one species to the next.

• This is not the case!!!• Fossil record shows few smoother inter-gradations from

one species to the next,– Species tend to appear suddenly in the fossil record

– Species linger for varying but often very extended periods of time in the fossil record

– Species disappear as suddenly as they arrived

– Species are replaced by other species which may or may not be closely related to them.

Current View of Human Evolution

• A modern view of human evolution maintains that it has occurred as a series of adaptive radiations

• The 1st radiation is that of the early bipedal apes – australopithecines

• The 2nd radiation involved the genus Paranthropus, a group of species that exploited low-grade vegetable food sources (nuts, root tubers and seeds) resulting in megadonts (very large teeth).

• The 3rd radiation is genus Homo, with the habilines and erectines developing a larger brain, diversifying and dispersing from Africa to other parts of the Old World.

• The last radiation does not involve any major evolutionary divergence, but reflects the dispersal of modern humans worldwide.

Hominin Evolution• Grouping of genera within the hominins is constantly changing.

• Previously only two or three hominid genera, Australopithecus, Paranthropus, and Homo, have been previously accepted, with Paranthropus considered a subgenus of Australopithecus by some authors.

• New discoveries since the mid 1990s have been assigned to as many as four new genera of the family Hominidae: Ardipithecus, Orrorin, Kenyanthropus, and Sahelanthropus.

• These specimens are described as having morphological traits that justify placing them in the family Hominidae while creating a new genus for the classification of each.

• Regardless of their final classifications, it is important to appreciate that fossil evidence can not identify any of these as a direct ancestor of Homo sapiens

• There are different schemes for the evolution of modern humans, and while there is broad agreement on many matters, some different opinions exist, as for example, how the various robust species are related.

• The gracile A. afarensis (Lucy) and A. africanus are accepted to be in the line that is ancestral to the human species in the genus Homo.

• As more fossil evidence is discovered, some of these differences will be resolved.

SahelanthropusEstimated age: 6 to 7 millon years oldBrain size: 350ccHeight: unknownPhysique: unknown as no bones below cranium and lower jaws discovered

yet so no predictions can be madeSkull Shape: • tall face, a thick brow ridge (probably a male feature), and a long and

narrow braincase Teeth and Jaws: • Dental arch is U-shaped with cheek teeth (molars, premolars) smaller

than Australopithecine ones• Dental enamel is thicker than Chimpanzee but thinner than

Australopithecine.• Canines don't project far above the other teeth as in Apes Geographical Distribution: Western Central Africa

Other Information:• Some scientists have pointed out the foramen magnum of Toumai is

positioned towards the back of the skull as in apes, indicating that the skull was held forward and not balanced on top of an erect body – an argument against bipedalism.

• Debate still about whether Toumai is a hominin, a fossil from before the point at which hominins separated from chimps, or even an early gorilla.

Orrorin tugenensisEstimated age: 6 millon years oldBrain size: unknownHeight: unknownPhysique:• Femur suggest bipedalism• About the size of a female chimpanzee (limb bones are about 1.5 times larger

than those of Lucy)• Adapted to both bipedality and tree climbingSkull Shape: unknownTeeth and Jaws: • teeth of O. tugenensis, suggest this species could even be more closely

related to Homo sapiens than the many Australopithecus species it predates. • Like our molars, the molars of O. tugenensis were small compared to any of

the australopithecine teeth. Their teeth also had very thick enamel like ours. Geographical Distribution: Eastern Africa

Other Information:• Claimed that australopithecines are an extinct offshoot. • Fragmentary nature of the remains (fragmentary arm and thigh bones, lower

jaws, and teeth) means some scientists have been skeptical of these claims so far

KenyanthropusEstimated age: 3.5 to 3.2 millon

years oldBrain size: 400-500ccHeight: unknownPhysique:• broad flat face. Skull Shape: Teeth and Jaws: small teeth Geographical Distribution: KenyaOther Information:• The name Kenyanthropus platyops

means "Flat faced man of Kenya".• mostly complete cranium which

came in two pieces: a skullcase which was heavily distorted, and a face which was much better preserved.

•

Ardipithecus ramidus

Estimated age: 4.4 million years oldBrain size: unknownHeight: 1.2mPhysique:• Possibly bipedal• Other fossils recovered with ramidus suggest it

was a forest dwellerSkull Shape: foramen magnum more forward

than apesTeeth and Jaws: • Smaller narrow molars; thinner jawGeographical Distribution: Eastern Africa

Ardipithecus ramidusOther information of interest• Remains have been discovered to as far back as 5.8 million

years. • Most remains are skull fragments. • Teeth are intermediate between those of earlier apes and

A. afarensis, but one baby tooth is very primitive, resembling a chimpanzee tooth more than any other known hominid tooth.

• More recently, a number of fragmentary fossils discovered between 1997 and 2001, and dating from 5.2 to 5.8 million years old, have been assigned first to a new subspecies, Ardipithecus ramidus kadabba (Haile-Selassie 2001), and then later as a new species, Ardipithecus kadabba (Haile-Selassie et al. 2004).

• One of these fossils is a toe bone belonging to a bipedal creature, but is a few hundred thousand years younger than the rest of the fossils and so its identification with kadabba is not as firm as the other fossils.

Genus: AustralopithecusBody form: ‘Gracile’Period: 5 to 2.3 million years agoDistribution: Eastern & Southern AfricaBrain Size: 400-500ccHeight: 1.0-1.3mBody Form: smaller and less robustSkull: more rounded and verticalSkull Crests: little evidence of crestsTeeth: large front and rear teeth, molars flat like humansWeight: 27kgLocomotion: bipedalTool Use: no evidence

Species identified: • A. anamensis, A. afarensis, A. africanus, A. garhi

Australopithecus anamensisEstimated age: 4.2 to 3.9 million year oldBrain size: unknownHeight: unknownPhysique:• Partial leg bones strongly suggest bipedalism• Humerus extremely humanlikeSkull Shape: primitive features in the skull, possiblly

apelikeTeeth and Jaws: • Very similar to those of older fossil apes, but canines

vertical• Teeth have thicker tooth enamel like in humansGeographical Distribution: Eastern AfricaOther Information: • Although the skull and skeletal bones are thought to be

from the same species, this is not confirmed

Australopithecus afarensisEstimated age: 3.9 to 2 million years agoBrain size: 375-550ccHeight: 1.07-1.52cmPhysique:• Light build• Some apelike features: relatively long arms, curved

fingers/toes, sexual dimorphism (females smaller than males)

Skull Shape: apelike face, low forehead, bony brow ridge, flat nose, no chin

Teeth and Jaws: • Human-like teeth, canines smaller than apes but larger

and more pointed than humans• Jaw shape is halfway between that of an ape and a human• Large back teethGeographical Distribution: Eastern Africa

Australopithecus afarensisOther Information: • Adapted to walking rather than

running• Bones show that they were

physically very strong• Curved fingers and hands

suggested by most scientists to be evidence that afarensis was still partially adapted to climbing in trees (some scientists thing this is not true – curved fingers were evolutionary ‘baggage’)

• Famous fossil “Lucy” was found in Ethiopia in 1974. She is very complete

Australopithecus africanusEstimated age: 3 to 2 million years agoBrain size: 420-500cc (larger than chimps despite similar body

size)Height: 1.1-14mPhysique:• Light build• Probably long arms• More human features, probably less sexual dimorphismSkull Shape: • Brow ridges less prominent• Higher forehead and shorter faceTeeth and Jaws: • Teeth and jaws much larger than in human, but far more similar

to human teeth than those of apes• Shape of jaw full parabolic like humans• Canine teeth further reduced compared to afarensisGeographical Distribution: Southern Africa

Australopithecus garhiEstimated age: ~2.5 million years oldBrain size: 450ccHeight: unknownPhysique:• Humanlike ratio of humerus and femur but apelike ratio of lower and

upper armSkull Shape:• sagittal crest for anchoring large temporal (chewing) muscles Teeth and Jaws: • Extremely large teeth, especially at rear when compared to other

australopithecine species• rectangular or slightly diverging dental arcade (i.e. more apelike)• Some primitive features as seen in A. afarensis but not in A. africanusGeographical Distribution: Ethiopia Other Information: • Not definite that skeletal remains of arms and legs belong to same species

as partial skull that is identified as garhi• Along with other species mentioned are known as gracile

australopithecines, because of their relatively lighter build, especially in the skull and teeth. (Gracile means "slender", and in paleoanthropology is used as an antonym to "robust".) Despite this, they were still more robust than modern humans.

Genus: ParanthropusBody form: ‘Robust’Period: 2.5 to 1.3 million years agoDistribution: Eastern & Southern AfricaBrain Size: 500-530ccHeight: 1.4-1.5mBody Form: larger, more heavily builtSkull: flatter, tear-drop shapedSkull Crests: nuchal and sagittal crestsTeeth: smaller front, large rear teethWeight: 45kgLocomotion: bipedalTool Use: minimal evidence

Species identified:• P. aethiopicus, P. robustus, P. boisei

Paranthropus aethiopicusEstimated age: 2.3 to 2.6 million years oldBrain size: 410ccHeight: unknownPhysique:• unknownSkull Shape: • Hind portions are very primitive, most resembling A. arafensis• Massive (broad face)• Largest sagittal crest in any known homininTeeth and Jaws: • Large teethGeographical Distribution: Ethiopia Other Information: • Known primarily from one major specimen – the Black Skull, it

may be an ancestor or P. robustus and P. boisei but has a baffling mixture of primitive and advanced traits

Paranthropus robustusEstimated age: 2.2 to 1.5 million yearsBrain size: 530ccHeight: 1.1-1.3mPhysique:• Body similar to A. africanus• Heavy build• Relatively long arms• Moderate sexual dimorphismSkull Shape: • Long, broad, flat face• Crest on top of skull• Moderate facial buttressingTeeth and Jaws: • Very thick jaws• Small incisors and canines, large molar like pre-molars and very large molarsGeographical Distribution: Southern AfricaOther Information: • Massive grinding teeth in a large lower jaw and presence of sagittal crests suggests

its diet would have been mostly coarse, tough food that needed a lot of chewing.• Bones excavated with robustus skeletons indicate that they may have been used as

digging tools.

Paranthropus boiseiEstimated age: 2.6 to 1.2 million years agoBrain size: 410-530ccHeight: 1.2-1.4mPhysique:• Similar to P. robustus• Very heavy build• Relatively long arms• Marked sexual dimorphismSkull Shape: • Long, broad, flat face• Large crest on top and back of skull• Facial buttressingTeeth and Jaws: • Very thick jaws• Small incisors and canines, large molar like pre-molars and very large

molarsGeographical Distribution: Eastern AfricaOther Information: • A few experts consider boisei and robustus to be variants of the same

species.

Genus: Homo• The Homo genus is separated from the earlier hominins

because of the emergence of tool use, language, and culture.• Begins about 2.3 million years ago. • The characteristics of these species are:

– bigger brain – forehead rises straight up– skull becomes rounder – teeth are reduced– arms are shorter– legs are longer– skeleton becomes more delicate.

• Scientists recognise 8 species at this stage not including modern humans. We will focus on those about which most is known.

Homo habilis (small)Estimated age: 2 to 1.6 million years agoBrain size: 500-650ccHeight: 1mPhysique:• Relatively long armsSkull Shape: • Small face with developed noseTeeth and Jaws: • Smaller, narrow molars• Thinner jawGeographical Distribution: Eastern and possibly Southern AfricaOther Information: • H. habilis, "handy man", was so called because of evidence of tools found

with its remains. • The bulge of Broca's area, essential for speech, is visible in one habilis

brain cast, and indicates it was possibly capable of rudimentary speech Sexual dimorphism may have existed

• Some scientists group this species with Homo habilis (large variant) also known as Homo rudolfensis to form one species. Other scientists believe variation between the two is too wide for a single species.

Homo habilis (large)also known as Homo rudolfensisEstimated age: 2 to 1.6 million years agoBrain size: 600-800ccHeight: 1.5mPhysique:• Robust but ‘human’ skeletonSkull Shape: • Larger, flatter faceTeeth and Jaws: • Large, narrow molars• Robust jawGeographical Distribution: Eastern AfricaOther Information: • H. habilis, "handy man", was so called because of evidence of tools found

with its remains. • The bulge of Broca's area, essential for speech, is visible in one habilis

brain cast, and indicates it was possibly capable of rudimentary speech Sexual dimorphism may have existed

• Some scientists group this species with Homo habilis (small variant) to form one species. Other scientists believe variation between the two is too wide for a single species.

Homo erectus(Homo ergaster for older African forms)Estimated age: 1.8 to 0.3 million years oldBrain size: 750-1250ccHeight: 1.3-1.5mPhysique:• Robust but ‘human’ skeletonSkull Shape: • Flat, thick skull with sagittal ‘keel’ and large brow ridgeTeeth and Jaws: • Smaller teeth than H. habilis• Robust jaw in larger individualsGeographical Distribution: Africa, Asia, Indonesia and possibly EuropeOther Information: • Body proportions vary; the “Turkana Boy” is tall and slender (though still

extraordinarily strong), like modern humans from the same area, while the few limb bones found of “Peking Man” indicate a shorter, sturdier build.

• H. erectus may have been more efficient at walking than modern humans, whose skeletons have had to adapt to allow for the birth of larger-brained infants

• There is evidence that erectus probably used fire, and their stone tools are more sophisticated than those of habilis.

Homo heidelbergensis(Archaic Homo sapiens)Estimated age: 400,000 to 100,000Brain size: 1100-1400ccHeight: unknownPhysique:• Robust but ‘human’ skeleton• Less robust than H. erectusSkull Shape: • Higher cranium, face less protruding, skull more roundedTeeth and Jaws: • Similar to H. erectus but smaller teethGeographical Distribution: Africa, Asia and Europe Other Information: • Many still have large brow ridges and receding foreheads and

chins. • No clear dividing line between late erectus and archaic sapiens,

and many fossils between 500,000 and 200,000 years ago are difficult to classify as one or the other.

Homo neanderthalensis (The Neanderthals/Neandertals)Also Homo sapiens neanderthalensis Estimated age: 150,000 to 30,000 years old (some evidence suggests

230,000)

Brain size: 1200-1750cc

Height: 1.5-1.7m

Physique:• Robust but ‘human’ skeleton• Adapted for cold• Bones are thick and heavy, and show signs of powerful muscle

attachments• Minor anatomical differences from modern humans, the most

unusual being some peculiarities of the shoulder blade, and of the pubic bone in the pelvis.

Skull Shape: • Reduced brow ridge, midface projection, long low skull

Teeth and Jaws: • Similar to H. heidelbergensis except for incisors and smaller teeth

Geographical Distribution: Europe and Western Asia

Homo neanderthalensis(The Neanderthals/Neandertals)Other Information: • Neanderthals would have been extraordinarily

strong by modern standards• Their skeletons show that they endured brutally

hard lives. • A large number of tools and weapons have been

found, more advanced than those of Homo erectus. • Neanderthals were formidable hunters, and are

the first people known to have buried their dead, with the oldest known burial site being about 100,000 years old.

• Western European Neanderthals usually have a more robust form, and are sometimes called "classic Neanderthals". Neanderthals found elsewhere tend to be less excessively robust.

Homo floresiensisEstimated age: 38,000 to 18,000 years ago Brain size: 417ccHeight: 1mPhysique:• About the size of a three-year old Homo sapiens [modern human]

child, but with a braincase only one-third as large• Slightly longer armsSkull Shape: • Hard, thicker eyebrow ridges than Homo sapiens• Sharply sloping forehead no chin• No chin Teeth and Jaws: no descriptionGeographical Distribution: Indonesian island of FloresControversy: • Is this a genuine new species or example of Homo sapiens with

genetic defect such as microcephaly (disease with decreased brain size and intellect) or Laron syndrome (insensitivity to growth hormone)

Homo floresiensisOther Information: • Archeological evidence suggests it lived at Liang Bua

between at least 95,000 and 13,000 years ago – this differs from age of fossils dated so far.

• H. floresiensis used stone tools and fire, and hunted pygmy elephants (mostly juvenile ones), Komodo dragons, and the giant rats found on Flores.

• Combined with the fact that Flores remained isolated during the most recent glacial period, it has been suggested that the species or its ancestors could have only reached the isolated island by water transport and this perceived evidence of advanced technology and cooperation on a modern human level has prompted the discoverers to hypothesize that H. floresiensis almost certainly had language

• Local geology suggests that a volcanic eruption on Flores was responsible for the demise of H. floresiensis in the part of the island under study at approximately 12,000 years ago, along with other local fauna, including the dwarf elephant Stegodon.

Homo floresiensisOther Information: • Significantly overlapped in time with Homo

sapiens, who arrived in the region sometime between 55,000 and 35,000 years ago.

• How they interacted, however--if they ever even met face to face--remains a mystery.

• This species may have survived longer in other parts of Flores to become the source of the Ebu Gogo stories told among the local people.

• The Ebu Gogo are said to have been small, hairy, language-poor cave dwellers on the scale of H. floresiensis.

• Widely believed to be present at the time of the arrival of the first Portuguese ships during the 16th century, these strange creatures were apparently last spotted as recently as the late 19th century.

Homo sapiens sapiens(Early anatomically modern humans)Estimated age: 160,000 to 60,000Brain size: 1200-1700ccHeight: 1.6-1.85mPhysique:• Modern skeleton possibly adapted for warmthSkull Shape: • Small or no brow ridge, shorter and higher skullTeeth and Jaws: • Teeth may be smaller• Shorter jaws than Neanderthals• Chin developedGeographical Distribution: Africa and Western

Asia

Homo sapiens sapiens(Early anatomically modern humans)Other Information: • Even within the last 100,000 years, the long-term trends towards smaller

molars and decreased robustness can be discerned. • The face, jaw and teeth of Mesolithic humans (about 10,000 years ago)

are about 10% more robust than ours. • Upper Paleolithic humans (about 30,000 years ago) are about 20 to 30%

more robust than the modern condition in Europe and Asia. • These are considered modern humans, although they are sometimes

termed "primitive". • Interestingly, some modern humans (aboriginal Australians) have tooth

sizes more typical of archaic sapiens. • The smallest tooth sizes are found in those areas where food-processing

techniques have been used for the longest time. This is a probable example of natural selection which has occurred within the last 10,000 years (Brace 1983).

• About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started becoming markedly more sophisticated, using a wider variety of raw materials such as bone and antler, and containing new implements for making clothing, engraving and sculpting.

• Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and animals, clay figurines, musical instruments, and spectacular cave paintings appeared over the next 20,000 years.

Origin of modern humans• Two main competing theories of the origin of modern humans

(Homo sapiens) are the Out-of-Africa or Replacement hypothesis and the Regional Continuity or Multiregional Hypothesis.

• Each of these hypotheses has contrasting predictions:

• Out-of-Africa Hypothesis– Modern humans should appear first in Africa and only later in other

parts of the world.– Transitional forms from ancestral to modern humans should be found

only in Africa.– Variation in mtDNA should be greater in African populations than in

other populations.

• Regional Continuity Hypothesis– Modern humans should appear throughout Africa, Asia and Europe

during the same period.– Transitional forms should be found in Africa, Europe and Asia.– Variation in mtDNA should be about equal in human populations from

all regions of the Old World.

Origin of modern humans

• Regardless of whether we interpret mtDNA results and fossil evidence to support the Out-of-Africa hypothesis or suggest that there may have been a number of waves of migration and interbreeding of populations……..

• mtDNA studies, combined with studies of Y chromosome DNA and other nuclear DNA sequences, strongly support the conclusion that small groups of Homo sapiens dispersed from Africa about 100,000 years ago and that their genes can be found all over the planet.

What’s so special about mtDNA

• mtDNA is passed down the maternal line, so all modern humans can trace their evolutionary heritage to a single woman via changes in mitochondrial DNA.

• This woman, dubbed “Eve” lived about 200,000 years ago in Africa.

• The descendents of this population of modern humans dispersed throughout the world.

• The question is:– Did they displace all other humans (Out-of-Africa

Hypothesis)?or

– did they breed with other human populations (Multiregional Hypothesis)?

• Important to realise that “Eve” was not the only woman around at this time – she is the only woman to which we can trace a continual inheritance of mtDNA ie she must have had daughters as well as, or instead of sons

The Dispersal of Modern Humans

• An African origin is probable, with south eastern Africa being the most likely place

• The dispersal was affected at crucial stages by the presence or absence of ‘land bridges’ formed during the drop in sea levels that occurs with the onset of ice ages

• The late development of boats and rafting allowed dispersal into Australia and the Pacific

Early humans in Australia

• Early humans entered Australia from S.E. Asia.

• Oldest fossil skeleton provides date of 40000 years ago but evidence of fire suggests it may be 100000 years ago

• Migration of humans to Australia was assisted by the low sea levels of the Pleistocene glacial periods which exposed land bridges.

• Activities of early Australians, together with glacial climate change led to changes in the Australian environment.