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 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 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 characteristics compared 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 Nakedness Retention 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 Bipedalism Position 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 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 tend to appear suddenly in the species to the next, 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. Genus: Australopithecus Genus: Australopithecus Body form: Gracile Period: 5 to 2.3 million years ago Distribution: Eastern & Southern Africa Brain Size: 400-500cc Height: 1.0-1.3m Body Form: smaller and less robust Skull: more rounded and vertical Skull Crests: little evidence of crests Teeth: large front and rear teeth, molars flat like humans
Weight: 27kg Locomotion: bipedal Tool Use: no evidence Species identified: A. anamensis, A. afarensis, A. africanus, A. garhi Australopithecus anamensis Estimated age: 4.2 to 3.9 million year old Brain size: unknown Height: unknown Physique: Partial leg bones strongly suggest bipedalism Humerus extremely humanlike Skull Shape: primitive features in the skull, possiblly apelike Teeth and Jaws: Very similar to those of older fossil apes, but canines vertical Teeth have thicker tooth enamel like in humans Geographical Distribution: Eastern Africa Other Information:
Although the skull and skeletal bones are thought to be from the same species, this is not confirmed Australopithecus afarensis Estimated age: 3.9 to 2 million years ago Brain size: 375-550cc Height: 1.07-1.52cm Physique: 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 teeth Geographical Distribution: Eastern Africa Australopithecus afarensis Other 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 africanus Estimated age: 3 to 2 million years ago Brain size: 420-500cc (larger than chimps despite similar body size) Height: 1.1-14m Physique: Light build Probably long arms More human features, probably less sexual dimorphism Skull Shape:
Brow ridges less prominent Higher forehead and shorter face Teeth 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 afarensis Geographical Distribution: Southern Africa Australopithecus garhi Estimated age: ~2.5 million years old Brain size: 450cc Height: unknown Physique: Humanlike ratio of humerus and femur but apelike ratio of lower and upper arm Skull 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. africanus
Geographical 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 Genus: Paranthropus Genus: Paranthropus Body form: Robust Period: 2.5 to 1.3 million years ago Distribution: Eastern & Southern Africa Brain Size: 500-530cc Height: 1.4-1.5m Body Form:
larger, more heavily built Skull: flatter, tear-drop shaped Skull Crests: nuchal and sagittal crests Teeth: smaller front, large rear teeth Weight: 45kg Locomotion: bipedal Tool Use: minimal evidence Species identified: P. aethiopicus, P. robustus, P. boisei Paranthropus aethiopicus Estimated age: 2.3 to 2.6 million years old Brain size: 410cc Height: unknown Physique: unknown Skull Shape: Hind portions are very primitive, most resembling A. arafensis
Massive (broad face) Largest sagittal crest in any known hominin Teeth and Jaws: Large teeth Geographical 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 robustus Estimated age: 2.2 to 1.5 million years Brain size: 530cc Height: 1.1-1.3m Physique: Body similar to A. africanus Heavy build Relatively long arms Moderate sexual dimorphism Skull Shape: Long, broad, flat face Crest on top of skull Moderate facial buttressing
Teeth and Jaws: Very thick jaws Small incisors and canines, large molar like pre-molars and very large molars Geographical Distribution: Southern Africa Other 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 boisei Estimated age: 2.6 to 1.2 million years ago Brain size: 410-530cc Height: 1.2-1.4m Physique: Similar to P. robustus Very heavy build Relatively long arms Marked sexual dimorphism Skull Shape: Long, broad, flat face Large crest on top and back of skull Facial buttressing
Teeth and Jaws: Very thick jaws Small incisors and canines, large molar like pre-molars and very large molars Geographical Distribution: Eastern Africa Other Information: A few experts consider boisei and robustus to be variants of the same species. Genus: Homo 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 ago Brain size: 500-650cc Height: 1m Physique: Relatively long arms Skull Shape: Small face with developed nose Teeth and Jaws: Smaller, narrow molars Thinner jaw Geographical Distribution: Eastern and possibly Southern Africa Other 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 rudolfensis Estimated age: 2 to 1.6 million years ago Brain size: 600-800cc Height: 1.5m Physique: Robust but human skeleton Skull Shape: Larger, flatter face Teeth and Jaws: Large, narrow molars Robust jaw Geographical Distribution: Eastern Africa Other 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 old Brain size: 750-1250cc Height: 1.3-1.5m Physique: Robust but human skeleton Skull Shape: Flat, thick skull with sagittal keel and large brow ridge Teeth and Jaws: Smaller teeth than H. habilis Robust jaw in larger individuals Geographical Distribution: Africa, Asia, Indonesia and possibly Europe Other 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 100,000 Brain size: 1100-1400cc Height: unknown Physique: Robust but human skeleton Less robust than H. erectus Skull Shape: Higher cranium, face less protruding, skull more rounded Teeth and Jaws: Similar to H. erectus but smaller teeth Geographical 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 Also Homo sapiens neanderthalensis Neanderthals/Neandertals) 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 floresiensis Estimated age: 38,000 to 18,000 years ago Brain size: 417cc Height: 1m Physique: About the size of a three-year old Homo sapiens [modern human] child, but with a braincase only one-third as large Slightly longer arms Skull Shape: Hard, thicker eyebrow ridges than Homo sapiens Sharply sloping forehead no chin No chin Teeth and Jaws: no description Geographical Distribution: Indonesian island of Flores Controversy: 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 floresiensis Other 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 floresiensis Other 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 60,000 Brain size: 1200-1700cc Height: 1.6-1.85m
Physique: Modern skeleton possibly adapted for warmth Skull Shape: Small or no brow ridge, shorter and higher skull Teeth and Jaws: Teeth may be smaller Shorter jaws than Neanderthals Chin developed Geographical Distribution: Africa and Western Asia Homo sapiens sapiens (Early anatomically modern Other Information: humans) 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. Whats 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 An African origin is probable, with south eastern Africa Humans 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.