Human Evolution PDF

HUMAN ORIGIN  Origin of people fascinate us ! Charles Darwin – 1858 -' On the Origin of species’ – suggested that humans and apes share a common ancestor 1774 -James Burnet suggested humans are related to orangutans – All intermediate animals through which our ancestors g...

HUMAN ORIGIN  Origin of people fascinate us ! Charles Darwin – 1858 -' On the Origin of species’ – suggested that humans and apes share a common ancestor 1774 -James Burnet suggested humans are related to orangutans – All intermediate animals through which our ancestors gradually changed to humans may be found in Africa. Many scientists think he was right. – but our common ancestors was not necessarily the the orangutan  Classification of humans- our place in the Animal Kingdom Then genus Homo Finally species Homo sapiens This is all shown in the picture alongside. Here we often come across the terms hominid and hominin. Classification of Humans  Hominid refers to the group which contains modern humans, chimpanzees, gorillas and orangutans. It also includes all their immediate ancestors. In other words all the organisms found in the family Hominidae. Hominin refers to modern humans and all the extinct human species. It also includes all our immediate ancestors. Earlier humans belong to a lot of species: – Homo habilis, – Homo erectus, APE-MEN? – Homo neanderthalensis. Relationship of humans to other primates SOMETHING EXTRA: Phylogentic Trees: A phylogentic tree shows the evolutionary relationships amongst different species.  It also represents a hypothesis about the history of a certain group of organisms.  This history mentioned above is based on a set of characteristics. SOMETHING EXTRA: A phylogentic tree may look like either of the diagrams shown alongside. Some phylogentic trees  Now lets look at what information these trees show us… SOMETHING EXTRA: Lets start with A.  A is called the ancestral stock.  It is found at the base of the phylogentic tree.  All the taxonomic groups on this tree arose from this ancestor. A Phylogentic Tree SOMETHING EXTRA: Now lets look at B  B is called the point of divergence.  It is the point where a new species evolved from the ancestral stock.  This new species can be the ancestor of a new taxonomic group.  We must remember that the ancestral stock B continues to exist, but it can undergo evolutionary change. Ancestral stock Phylogentic Tree SOMETHING EXTRA: Now lets move onto C.  C shows the formation of a 1 2 3 new species.  This is where C diverges leading to the formation of a new species 1 and 2. C  We can see that the tree also shows close relationships.  For example 1 and 2 are closely related because they are twigs of the same branch. Ancestral stock  While 3 is on a separate branch therefore not closely related to 1 and 2. Phylogentic Tree SOMETHING EXTRA: Finally lets look at D. 4  D shows that the D ancestral stock continues to exist but has undergone evolutionary change and Ancestral stock diversified to become phylum 4. Phylogentic Tree Characteristics we share with other primates  1. The upper limbs/front limbs Primates have long upper arms which can move freely – Swallow glenoid cavity - the head of the humerus fits into it – scapulae - not attached to spine Primate can rotate joints at least 180 ° Primate have flat nails instead of claws – the bare fingers are rich in nerve endings – making them sensitive for work and and use of tools.  The opposable thumb - powergrip an precision grip  All primates have thumbs which work in the oppisite direction to their fingers – opposable thumbs Thumb can pressed against the fingers – power grip – grasping tree branches and climbing. Also can use fingers and thumbs in a precision grip.  2. The brain Have large brains compared to their body masses. Can sense a large number of information. Parts of the brain that interpret information coming from the hands and eyes are enlarged. Parts of the brain interpreting the sense of smell is reduced since the sence of smell is less useful to primates.  Vision Early primates had to move quickly through the trees. Eyes infront – focus on the same object. Looking at an object with both eyes – binocular vision – gives a wider field of view Observing the solid nature of an object – stereoscopic vision Eyes also have cones and rods for colour vision and greater clarity of vision.  Number of offspring Primates have fewer offspring than many other mammals. Their young are dependent on their parents for much longer. Long period of interaction allows the adults to teach the young survival skills.  5. Upright posture Primates have the ability to sit upright with their head held high. – Better view of the surroundings – Allows the animal to walk on two legs and the upper limbs can carry food, tools and babies. Characteristics that make us different from other primates  Bipedalism All primates can sit upright and can walk on two feet from time to time. Humans walk on two feet all the time, which makes us different from all other primates. Advantages of bipedalism: – Hands became free for carrying food, tools and babies – Better view of the surroundings in search for food and predators – Movement from place to place becomes more efficient – Faster cooling of body – Display of male sex organs as part of courtship behaviour Relative positions of the Foramen mangnum Quadrupedal + bipedal H – in a forward position P – towards back of skull The shape of the spine: Human spine is curved so the upper body is directly above the pelvis when standing erect – a more curved spine (S-shaped spine). Other primates spine less curved. Asa result, when standing erect, the weight pulls it forward, making upright stance unsteady – less curved spine (C-shaper spine). Shape of the pelvic girdle: Human pelvis (short and wide) is better able to support the vertically stacked organs. Other primates pelvis (long and narrow), is adapted to quadrupedal knuckle walking, providing greater rigidity.  2. A flat face Homo sapiens flat faces makes us different from earlier species - Homo habilis, Homo erectus and Homo neanderthalensis. Our faces appear flat because: – Our foreheads do not slope backwards as those of the ape men – Our lower jaws have a well-developed chin – Bones of the nose and jaws do not stick out as much as those of ape men – not prognathous – Our brow ridges are not as pronounced as those of ape men Nutcracker Man ? 3. Shape of jaws  3. Dentition The general dental formula of mammals: 3:1:4:3 3:1:4:3 3 :incisors 1 :canine 4 :pre-molares 3 : molares Humans have the same dental formula as apes: 2:1:2:3 2:1:2:3 Humans have smaller canines and smaller spaces between their teeth than other primates.  4. An enlarged brain Modern humans have brain sizes from 1 200 ml to 1 800 ml, with a average brain size being 1 400 ml. Generally speaking, animals with larger brain sizes compared to their body masses are more intelligent than those with smaller brain sizes compared to theit body masses When it comes to modern humans this rule does not apply There are highly intelligent people with relatively small brain sizes, some as small as 1 200 ml. Cranial ridges disappeared and primates across the top of cranium. P 221 Table about skull  5. Language Gorillas communicate by means of 22 different sounds Chimpanzees have an even larger range of sounds This sounds may be considered to be the natural languages of these apes. Humans can learn to communicate in artificial languages such as English, Afrikaans, isZulu, Tswana This led to the development of human culture.  Tracing the sequence of human evolution p 223 Scientists believe that factors that led to the evolution of all other organisms, also led to the development of humans Scientists do not all agree on how, when and where modern humans developed. They do agree on the general pattern of human development and that chimpanzees are our closest living relatives. We share 98% of our DNA sequences with chimpanzees. It is important to note that they not saying that we have envolved from chimpanzees.  They are saying that we and chimpanzees probably share a common ancestor. The general pattern of human development that most scientists generally agree on is as follows: Ape-like ancestor > ape men > early humans > modern humans Lines of evidence that support the idea of common ancestors for living hominids including humans: Fossil evidence Genetic evidence – Mitochondrial DNA Cultural evidence – tool-making  FOSSIL EVIDENCE Earliest hominin species Ardipithecus ramidus is resent discovered in Ethiopia (The Rift Valley in East Africa). Fossils only found in Africa and SA. Existed 5-4 mya Discovered by Tom White. An intermediate between apes and humans Characteristics: 1,2 m tall, weight of about 50 kg Small brain – 300 to 350 ml Like common chimpanzees –large brow ridges, prognathous. Smaller canines Adapted for bipedal walking and climbing trees.  4 to 1,6 million years ago Australopithecines – ape men (TB p 224) Australopithecus afarensis: (Lucy) – existed 4 – 2,7 mya Fossil site: Ethiopa, Kenya, Tanzania (only Africa) Discovered: Donald Johansen Australopithecus africanus (Taung child, Mrs Ples, Little foot – existed 3 – 2 mya Fossil site: Taung, Sterkfontein (only Africa and SA) Discovered: Raymond Dart, Robert Broom, Ron Clarke Australopithecus sediba (Karabo) – existed 2,0 – 1,6 mya Fossil site: Malapa Cave (only Africa and SA) Discovered: Lee Berger  Australopithecus afarensis Lucy Lived about 4-2,7 mya The forward position of the foramen magnum suggested that it was bipedal Table Slide 47 Laetoli footprints Discovered by Mary Leakey – clear evidence for bipedalism  Australopithecus africanus Taung child Is about 2.6 to 2.8 million years old The forward position of the foramen magnum suggested that it was bipedal It had an ape-like head, but dentition like that of a baby human. Discovered in 1924 by Raymond Dart outside the village of Taung in the North-West Province Brain little larger than chimpanzee Table slide 47  Mrs Ples Australopithecus africanus An adult form of the Taung child Lived about 2 million years ago Discovered by Robert Broom in the Sterkfontein caves (1947). Originally, it was given the name Plesianthropus (Mrs Ples) In 2002, Francis Thackeray, a paleoanthropologist, concluded that Mrs Ples was a male Table slide 47  Little Foot Australopithecus africanus Is about 3.9 to 4.2 million years old. Discovered by Ron Clarke, in Sterkfontein caves. Carefully chiseling away of the hard rock around the fossil showed that it was almost the entire skeleton of an early hominid. In October 2006, the fossil was brought to the surface. Table slide 47 The scull and upper vertebral collumn of Little foot  KARABOU – Australopithecus sediba 15 August 2008 – 9 year old boy Mathew Berger found lower jaw and clavicle at Malapa site in Cradle of Humankind. Lee Berger and team from Wits found skull in March 2009. Named it Australopithecus sediba (Table – slide 47) Lived about 1,78 to 1.98 million years ago Scientists think it was transitional between Australopithecus africanus and Homo habilis or Homo erectus – a possible ancestor to the genus Homo  Australopithecus - characteristics A. afarensis A. africanus A. sediba Height 110-150 cm 110-135 cm 130-150 cm Brains size 375-550 ml 420-620 ml 420 ml Foramen magnum Forward position Forward position Forward position Brow ridges Large/heavy Present, smaller Present, smaller than A. afarensis than A. africanus Cranial ridges None None None Jaws Very prognathous Prognathous Less prognathous Canines Large, pointed Not very long Not very long Pelvis Intermediate – Bipedal Bipedal bipedal & tree  Australopithecus robustus Fossils of this species have been found only in SA. Classification as Australopithecus is uncertain. This species, together with another species (A. boisei- Found by Mary and Louis Leakey ) from Tanzania, are now identify as of the genus Parantropus.  HOMO SPECIES The genus Homo consists of the one still- living species – Homo sapiens. All modern humans belong to it. Between 15 – 20 species are extinct, including Homo habilis, Homo erectus and Homo naledi. Most significant difference between this genus and Australopithecus – much larger brain Homo habilis Existed 2,2 – 1,6 mya Fossil site – Olduvai – Tanzania –discovered by Peter Nzube Discovered by Louis & Mary Leaky Homo erectus Existed 2 – 0,4 mya Fossil site – Java, Indonesia also SA and Kenya Discovered Eugene Dubois Homo naledi Existed 0,335 – 0,236 mya Cradle of human kind – Rising Star cave Discovered Lee Berger Homo sapiens Existed 0,2 mya to present Fossil site – Omo, Ethiopia, Makapansgat in Limpopo Discovered Richard Leakey  HOMO SPECIES Scientists believe that Australopithecines gave rise to many lines or branches of development. 2million years ago Homo habilis – firts early humans Like Australopithecus but 110-130 cm foramen magnum – forward position pelvis adapted for bipedal less pronounced brow ridges, small canines a flatter face – jaws less prognathous a more rounded head and a bigger brain (650 ml) and no cranial ridges Also referred to as handy man, because they made and used tools. 2 million years ago Homo habilis gave rise Homo erectus – like Austrolopithecus + Homo habilis but with bigger brain (900 -1000 ml) and small cranial ridges Height 160-180 cm foramen magnum – forward position pelvis adapted for bipedal Small brow ridges, small and short canines a flatter face – jaws less prognathous Used fire and their stone tools are more sophisticated. 2 million years ago Homo erectus gave rise Homo sapiens – but with bigger brain (1200-1800 ml) and no cranial ridges Height 160-180 cm foramen magnum – forward position pelvis adapted for bipedal No brow ridges, small teeth a flatter face – jaws not prognathous Lived alongside 4 other human species – Homo neanderthalensis, Homo antecessor, Homo florensiensis and Homo heidelbergensis (h) Today Only homo sapiens exists – others extinct  Trends in human development Most scientists today support the theory that modern humans and apes have a common ancestor. There is evidence to indicate that the following changes took place gradually in the development of humans: A shift of the foramen magnum to a forward position suggesting bipedalism The development of a more rounded skull An increase in cranium size – larger brain  A flatter face due to: a less sloping forehead less protruding jaws a more developed chin A more rounded jaw Increased size of skeleton which would mean increased height A change in dentition towards the human dental formula  Main fossil sites in SA p. 228 13 major fossil sites in Gauteng – given the official name The Sterkfontein, Swartkrans, Kromdraai and Environs World Heritage Site. Unofficially named as the Cradle of Humankind – scientists believed that the birthplace of all humans was in these sites – oldest fossils of austrolopithecines were found here. Fossils found here were: * Homonid species * 3 major stone tool cultures * Wide range of plant and animal fossils Scientists have interpreted these findings to mean the following: 3 million years ago, a hominid which was part ape and part human occupied Gauteng. (Australopithecus africanus) May have been one of the ancestors of modern man. Earliest members of the modern human – Homo habilis – lived in the Cradle about 2 million years ago. Homo habilis have given rise to Homo erectus and fossils have been found at Sterkfontein and Swartkrans. Able to make use of fire 1.2 million years ago. Lived together with another ape man – Paranthropus robustus – flatter-faced with big teeth and had the ability to make tools. One million years ago the ape men were all extinct.  Contribution of other African Countries, including the Great Rift Valley Scientists believed that the 3 million year old Auatralopithecus africanus was the oldest hominid fossil. This and the large number of other hominid fossils found in SA led them to believe that SA was the birthplace or cradle of humankind. A number of much older hominid fossils east of the Great Rift Valley in East Africa made scientists change their minds.  In 2001 the cranium of a 7 million year old fossil – Toumai – was found in Central Africa in Chad. Now the scientists believe that Central Africa was the cradle of humankind. In August 2012 Maeve Leakey, daughter-in-law of Louis and Mary Leakey found a fossil in Kenya which many consider to be a new species of Homo. Based on this they thought that East Africa was the cradle.  Genetic Evidence – also to support “Out of Africa hypothesis How DNA analysis is used Studies comparing DNA shared by humans and apes reveal that: Genetic difference between modern humans is very small –they share 99,9% of the same genes. Between humans and apes there is a slightly larger genetic difference, but still share large majority of their genes – between 96,9 and 98,8% Studies show that of the African apes, the chimpanzee is the closest relative of humans –share 98,8% of the same genes  Analysis of mitochondrial DNA is used to trace back our ancestors, as well as DNA from the Y-chromosome. A search is made for mutations - individuals who have the same mutation must share the same common ancestor. Mutations serve as markers of descent. DNA from the Y-chromosome Sex chromosomes of human females are XX males =XY. Major part of the Y-chromosome of males does not undergo crossing over with its mis-matched X chromosome. This means that most of the DNA on the Y-chromosome is passed on from father to son without being mixed with nucleotides from the mother. Mutant nucleotides can be traced from son to father to grandfather to great grandfather This is the way our male ancestry can be traced.  Mitochondriol DNA Every cell has mitochondria within where cellular respiration takes place. Mitochondria also contain DNA = mitochondriol DNA (mt DNA). It is handed down from mother to child. Mutant nucleotides in mitochondriol DNA, enables us to trace our female line of descent. Mitochondriol mutations take place at a faster rate = easer to trace the female lineage.  What does DNA analysis say about our ancestry? Mutant nucleotides on Y -chromosomal DNA was markers of descent. Spencer Wells and his colleagues – traced the lineage of every man alive to a common ancestor who lived in east Africa about 60 000 years ago. Analysis of mitochondriol DNA leads to an ancestral female who also lived in east Africa, around 150 000 years ago. Scientists believe that other species of humans, such as Homo erectus, Homo heidelbergensis, Homo neanderthalensis and Homo florensiensis were also present at this time.  Cultural evidence An important aspect of human evolution, separating humans from hominids – development of tools. Earliest tools – Homo habilis Better tools – Homo erectus Sophisticated tools –Homo sapiens Two other ascepts: Fire Art  The “Out of Africa” hypothesis p 235 Most scientists accept that humans originated in Africa. They migrated to all parts of the world. From the east Africa early humans migrated across the continent of Africa. They moved out of the continent through north-east Africa in several groups. Through many complex pathways they migrated into every habitable continent on Earth within 50 000 years. The hypothesis is based on: genetic evidence (all ready done) fossil evidence. See exam guideline p 17 Fossil Evidence for the 'out of Africa' Hypothesis Most scientists accept that Ardipithecus (only found in Africa), Australopithecus (only found in Africa including Karabo, Little foot, Taung child and Mrs Ples), Homo habilis (only found in Africa), and Homo erectus are all on the same line of development as Homo sapiens. (oldest fossils only found in Africa while younger fossils were found in other parts of the word), Fossil evidence show that all these human ancestors lived in Africa. 40% of early human ancestor fossils found in Gauteng