Understanding Human Evolution: From Ancestral Lineage to Modern Hominids
Human evolution is a fascinating journey of change and development, where humans emerged as a distinct species. The theory of evolution highlights our common ancestry with other organisms, including chimpanzees. Evidence from fossils, genetics, and culture supports the idea of a shared ancestor among living hominids. Characteristics like bipedalism and distinct skull features distinguish hominids from great apes, showcasing an evolutionary path towards modern humans.
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Human evolution Human evolution is the process of change and development by which humans emerged as a districted species Theory of evolution does not state that humans evolved from apes or from any other creature that lives today The theory says that all organisms are related to all other organisms in that we share a common ancestor Humans share a common ancestor with chimpanzees Palaeo-anthropologists believe that the common ancestor existed 6 to 8 million years ago Thereafter, this ancestral species split into two On line evolved into the great ape The other evolved into early humans called hominids
Evidence of common ancestor for living hominids Evolutionary theory does not state that humans evolved form chimpanzee or gorilla, but it does propose that they had a common ancestor The three main lines of evidence that indicates that hominids may have shared a common ancestor : Fossil evidence Genetic evidence Cultural evidence
Characteristics of hominids Hominids possessed certain characteristics that distinguished them from the great apes Bipedalism This means being able to walk on two legs. The evolution of bipedalism involved numerous anatomical adaptations including the following Fully upright standing position and walking movement Shortening of the arms relative to the legs Restructuring of the pelvic bones for weight bearing Restructuring of the foot for weight bearing, involving loss of toe opposability, Change in shape of the spinal column from straight to S-shaped Change of position in the foramen magnum to a more central position
Skull, brain size and dentition The skull in hominids had the following features that differ from the great apes: More rounded No prominent brow ridge Distinct nose and chin Prominent forehead Their brain size is about 3.5 times larger that that of the great apes with a well-developed frontal lobes responsible for higher thinking functions
Primate Fossils Australopithecus Homo erectus Homo sapiens
Dentition Hominids had small regular front teeth and very large molars relative to other primate species Reduced canine size is associated with the absence of a diastema which accommodates a large canine in ape and monkey species. Large molars may be an adaption to a diet based on relative hard vegetable foods such as nuts, berries and grains that were abundant in the grasslands
Prognathism Apes have large protruding jaws without a chin There jaws protrude beyond the upper part of the face, which results in a sloping face As the teeth becomes smaller over time, so the jaw became less protruding and more rounded. Face appears flatter les sloping Humans have a narrow, flat face with a rounded jaw and a protruding chin Forehead appears more vertical as a result of the larger cranium that contains a larger brain
Palate shape Pallet of apes is narrow and rectangular and became more U shaped over time In humans the palate became wider and more curved
Hands AS hands were no longer used for walking, they could evolve for other functions Hands showed increased manual dexterity, involving a lengthening and increased flexibility of the thumb to allow movements such as the following Gripping Cupping Spreading fingers apart Holding small objects
Cultural evidence Tools Language
Characteristics we share with primates Opposable thumb with power grip and precision grip Bare fingers Long arms Freely rotating arms Stereoscopic vision Eyes with cones(as well as rods) Large brain compared to body mass Portions of brain centers that process information from hands and eyes are enlarge Olfactory brain centers diminished Few offspring Upright posture and bipedalism
Characteristics that make us different from other primates Humans are always bipedal Flat face Dentition similar to that of monkeys and apes but different from old world primates Smaller canines Larger brain Artificial language
Evidence for ancestors of humans There has been at least a dozen hominid species that lived and become extinct We have evidence of these extinct species from fossil evidence from Africa, Asia and Europe. Most of the early hominids were dead end species This means that they become extinct without giving rise to a new species But we can link some of the extinct hominids directly to modern humans
Organism When organism existed 5-4 mya Fossil Site Discovered by Characteristics Ardipithecus ramidus North-East Ethiopia Tim White Brain size: 300-350ml Forward position of foramen magnum Very prognathous Heavy brow ridges Pelvis structure: bipedal and tree climbing Brain size: 375-550ml Forward position of foramen magnum Very prognathous Heavy brow ridges Canine large and pointed Long arms No cranial ridge Brain size: 428-625ml Forward position of foramen magnum Prognathous Brow ridges Teeth large, canines not long Long arms No cranial ridge Brain size: 420ml Less prognathous Brow ridges Large teeth, canines not long Long arms No cranial ridge Brain size: 650ml Less prognathous Less pronounced brow ridges Human-like teeth smaller canines Long arms Brain size: 900ml Prognathous Cranial ridges Short canines Longer legs and shorter arms Brain size: 1200 1800ml No brow ridges Small teeth Short arms Australopithecus afarensis 4 2,7 mya Ethiopia, Kenya, Tanzania Donald Johanson Australopithecus africanus 3 2 mya Taung; Sterkfontein Raymond Dart Australopithecus sediba 1,9 1,8 mya Malapa Cave in the cradle of humankind Lee Burger Homo habilis 2,2 1,6 mya Tanzania Louis and Mary Leakey Homo erectus 2 0,4 mya Java in Indonesia and then Swartkrans Homo sapiens 200 000 years ago - present Makapansgat in Limpopo; Border Cave in KZN; Blombos Cave in Western Cape
The Out of Africa hypothesis According to most scientists, humans originated from Africa and moved to other countries. This hypothesis is based on fossil evidence and genetic evidence from fossils of Africa Examples of fossils Mrs Ples, Taung Child, Little Foot (Australopithecus africanus)Nutcracker man(Paranthropus boisei):- Handy man(Homo habilis Toumai (Sahelanthropus tachadensis):- Karabo : (Australopithecus sediba)
When DNA is analysed for the purpose of tracing ancestry, a search is made for mutations since individuals who have the same mutation must share the same common ancestor These mutations serves as markers of decent DNA from Y chromosome AND Mutant genes from Mitochondrial DNA
Hominid fossil record in Africa Africa have made a great contribution to our understanding of human evolution Famous hominid fossil sites include the Cradle of humankind at Sterkfontien near Johannesburg and the great rift valley in East Africa
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