ADVERTISEMENTS:
Here is a compilation of essays on ‘Human Evolution’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Human Evolution’ especially written for school and college students.
Essay on Human Evolution
Essay Contents:
- Essay on the Introduction to Human Evolution
- Essay on the Origin of Apes and Hominids
- Essay on the History of Primates
- Essay on the Genus of Homo
- Essay on the Evolution of Neanderthals
- Essay on the Models of Human Evolution
ADVERTISEMENTS:
Essay # 1. Introduction to Human Evolution:
Evolution as a process is composed of two parts:
1. An organism reproducing mechanism that provides variable organisms. Changes to the organism are largely random and effect future generations. They are made without regard to consequences to the organism.
2. A changing environment which screens organism changes. The environment provides stress on the variable organisms that selectively allows, through competition, certain changes to become dominant and certain others to be eliminated, without consideration for the future of the mechanism.
ADVERTISEMENTS:
That same process provides mechanism (organism) disintegration if a strong screening environment is not present. Evolution is a two-way process which does not always work to the long term advantage of the organism and in fact often becomes quite deadly to a given species and thereby eradicates it.
The evolutionary process is bidirectional in its effect. It may, depending on the environment, either improve a given characteristic or decay it. Since the first step in the process is largely random and most organisms are quite complex, almost all of the variations are harmful.
A characteristic of a species advances if the environment is harsh, since most harmful variations to that characteristic will be eliminated through death and suffering at a rapid rate, leaving only the inconsequential and helpful changes in the lineage.
If the environment is benign with respect to the capability of the species then the harmful changes are not eliminated and the species will degenerate to a point of balance with the environment.
Human evolution is the part of biological evolution concerning the emergence of Homo sapiens as a distinct species from other hominans, great apes and placental mammals. It is the subject of a broad scientific inquiry that seeks to understand and describe how this change occurred.
Mammals developed from primitive mammal-like reptiles during the Triassic Period, some 200-245 million years ago. After the terminal Cretaceous extinction (65 million years ago) eliminated the dinosaurs, mammals as one of the surviving groups, underwent an adaptive radiation during the Tertiary Period.
The major orders of mammals developed at this time, including the Primates to which humans belong. Other primates include the tarsiers, lemurs, gibbons, monkeys, and apes. Although we have significant differences from other primates, we share an evolutionary history that includes traits such as opposable thumbs, stereoscopic vision, larger brains, and nails replacing claws.
Primates are relatively unspecialized mammals- they have no wings, still have all four limbs, cannot run very fast, have generally weak teeth, and lack armor or thick protective hides. However, the combination of primate adaptations that include larger brains, tool use, social structure, stereoscopic color vision, highly developed forelimbs and hands, versatile teeth, and upright posture, place them among the most advanced mammals.
Approximately 20 million years ago central and east Africa was densely forested. Climatic changes resulting from plate tectonic movements and episodes of global cooling about 15 million years ago caused a replacement of the forest by a drier-adapted savanna mixed with open areas of forest. During the course of hominid evolution, periodic climate changes would trigger bursts of evolution and/or extinction.
ADVERTISEMENTS:
Primates have modifications to their ulna and radius (bones of the lower arm) allowing them to turn their hand without turning their elbow. Many primates can also swivel or turn their arms at the shoulder. These two adaptations offer advantages to life in the trees.
Primates have five digits on their forelimbs. They are able to grasp objects with their forelimbs in what is known as a prehensile movement. A second modification makes one of the digits opposable, allowing the tips of the fingers and thumb to touch.
Placement of the eyes on the front of the head increases depth perception, an advantageous trait in tree-dwelling primates. Changes in the location of rods and cones in the eye adapted primates for color vision as well as peripheral vision in dim light.
Upright posture allows a primate to view its surroundings as well as to use its hands for some other task. Hominids, the lineage leading to humans, had changes in the shape and size of their pelvis, femur, and knees that allowed bipedalism (walking on two legs). The change from quadruped to biped happened in stages, culminating in humans, who can walk or run on two legs.
ADVERTISEMENTS:
Several trends of primate evolution are evident in the teeth and jaw. First, change in the geometry of the jaw reduced the snout into a flat face. Second, changes in tooth arrangement and numbers increased the efficiency of those teeth for grinding food. Third, about 1.5 million years ago our diet changed from fruits and vegetables to include meat.
Essay # 2. Origin of Apes and Hominids:
The fossil record indicates primates evolved about approximately 30 million years ago in Africa. One branch of primates evolved into the Old and New World Monkeys, the other into the hominoids (the line of descent common to both apes and man).
Fossil hominoids occur in Africa during the Miocene epoch of the Tertiary period. They gave rise to an array of species in response to major climate fluxes in their habitats. However, the nature of those habitats leads to an obscuration of the line that leads to humans (the hominids).
ADVERTISEMENTS:
Until a few years ago, the ramapiths were thought to have given rise to the hominids. We now consider ramapiths ancestral to the orangutang. The hominid line arose from some as-yet-unknown ancestor. Lacking fossil evidence, biochemical and DNA evidence suggests a split of the hominid from hominoid line about 6 to 8 million years ago.
Australopithecus afarensis, the first of the human-like hominids we know of, first appeared about 3.6-4 million years ago. This species had a combination of human (bipedalism) and apelike features (short legs and relatively long arms). The arm bones were curved like chimps, but the elbows were more human-like. Scientists speculate that A. afarensis spent some time climbing trees, as well as on the ground.
Australopithecus ramidus is an older species, about 4.4 million years, and is generally considered more anatomically primitive than A. afarensis. The relationship between the two species remains to be solved.
History of Man:
ADVERTISEMENTS:
I. Ardipithicus ramidus- 5 to 4 million years ago
II. Australopithecus anamensis- 4.2 to 3.9 million years ago
III. Australopithecus afarensis- 4 to 2.7 million years ago
IV. Australopithecus africanus- 3 to 2 million years ago
V. Australopithecus robustus- 2.2 to 1.6 million years ago
VI. Homo habilis- 2.2 to 1.6 million years ago
ADVERTISEMENTS:
VII. Homo erectus- 2.0 to 0.4 million years ago
VIII. Homo sapiens archaic- 400 to 200 thousand years ago
IX. Homo sapiens neandertalensis- 200 to 30 thousand years ago
X. Homo sapiens sapiens- 200 thousand years ago to present.
The role of A. afarensis as the stem from which the other hominids arose is in some dispute. About 2 million years ago, after a long million year period of little change, as many as six hominid species evolved in response to climate changes associated with the beginning of the Ice Age.
Two groups developed- the australopithecines, generally smaller brained and not users of tools; and the line that led to genus Homo, larger brained and makers and users of tools. The australopithecines died out 1 million years ago; Homo, despite their best efforts (atomic weapons, pollution) is still here!
ADVERTISEMENTS:
With an incomplete fossil record, australopithecines, at least the smaller form, A. africanus, was thought ancestral to Homo. Recent discoveries however have caused a reevaluation of that hypothesis. One pattern is sure, human traits evolved at different rates and at different times, in a mosaic- some features (skeletal, dietary) establishing themselves quickly, others developing later (tool making, language, use of fire).
A cluster of species developed about 2-2.5 million years ago in Africa. Homo had a larger brain and a differently shaped skull and teeth than the australopithecines. About 1.8 million years ago, early Homo gave rise to Homo erectus, the species thought to have been ancestral to our own.
Soon after its origin (1.8 million but probably older than 2 million years ago) in Africa, Homo erectus appears to have migrated out of Africa and into Europe and Asia. Homo erectus differed from early species of Homo in having a larger brain size, flatter face, and prominent brow ridges. Homo erectus is similar to modern humans in size, but has some differences in the shape of the skull, a receding chin, brow ridges, and differences in teeth.
Homo erectus was the first hominid to:
1. Provide evidence the social and cultural aspects of human evolution.
2. Leave Africa (living in Africa, Europe, and Asia).
3. Use fire.
4. Have social structures for food gathering.
5. Utilize permanent settlements.
6. Provide a prolonged period of growth and maturation after birth Between 100,000 and 500,000 years ago, the world population of an estimated 1 million Homo erectus disappeared, replaced by a new species, Homo sapiens. How, when and where this new species arose and how it replaced its predecessor remain in doubt. Answering those questions has become a multidisciplinary task.
Two hypotheses differ on how and where Homo sapiens originated:
1. The Out-of-Africa Hypothesis proposes that some H. erectus remained in Africa and continued to evolve into H. sapiens, and left Africa about 100,000-200,000 years ago. From a single source, H. sapiens replaced all populations of H. erectus.
Human populations today are thus all descended from a single speciation event in Africa and should display a high degree of genetic similarity. Support for this hypothesis comes from DNA studies of mitochondria- since African populations display the greatest diversity of mitochondrial DNA, modern humans have been in Africa longer than they have been elsewhere. Calculations suggest all modern humans are descended from a population of African H. sapiens numbering as few as 10,000.
2. The Regional Continuity Hypothesis suggests that regional populations of H. erectus evolved into H. sapiens through interbreeding between the various populations. Evidence from the fossil record and genetic studies supports this idea.
Scientists can often use the same “evidence” to support contrasting hypotheses depending on which evidence (fossils or molecular clock/ DNA studies) one gives more weight to. The accuracy of the molecular clock, so key to the out-of-Africa hypothesis, has recently been questioned.
Recent studies on the Y-chromosome seem to weaken the regional continuity hypothesis by indicating a single point-of-origin for our species some 270,000 years ago. Continued study will no doubt reveal new evidence and undoubtedly new hypotheses will arise. It is a task for all of us to weigh the evidence critically and reach a supportable conclusion, whether we are scientists or not.
Essay # 3. History of the Primates:
Before Homo:
The evolutionary history of the primates can be traced back for some 85 million years, as one of the oldest of all surviving placental mammal groups. Most paleontologists consider that primates share a common ancestor with the bats, another extremely ancient lineage, and that this ancestor probably lived during the late Cretaceous, together with the last dinosaurs. The oldest known primates come from North America, but they were widespread in Eurasia and Africa as well, during the tropical conditions of the Paleocene and Eocene.
With the beginning of modern climates, marked by the formation of the first Antarctic ice in the early Oligocene around 40 million years ago, primates went extinct everywhere but Africa and southern Asia. One such primate from this time was Notharctus.
Fossil evidence found in Germany 20 years ago was determined to be about 16.5 million years old, some 1.5 million years older than similar species from East Africa. It suggests that the primate lineage of the great apes first appeared in Eurasia and not Africa.
The discoveries suggest that the early ancestors of the hominids (the family of great apes and humans) migrated to Eurasia from Africa about 17 million years ago, just before these two continents were cut off from each other by an expansion of the Mediterranean Sea. These primates flourished in Eurasia and that their lineage leading to the African apes and humans —Dryopithecus—migrated south from Europe or Western Asia into Africa.
The surviving tropical population, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Fayum depression southwest of Cairo, gave rise to all living primates—lemurs of Madagascar, lorises of Southeast Asia, galagos or “bush babies” of Africa, and the anthropoids; platyrrhines or New World monkeys, and catarrhines or Old World monkeys and the great apes and humans.
The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya rift valley, dated to 24 mya (millions of years before present). Its ancestry is generally thought to be close to such genera as Aegyptopithecus, Propliopithecus, and Parapithecus from the Fayum, at around 35 mya.
There are no fossils from the intervening 11 million years. No near ancestor to South American platyrrhines, whose fossil record begins at around 30 mya, can be identified among the North African fossil species, and possibly lies in other forms that lived in West Africa that were caught up in the still-mysterious transatlantic sweepstakes that sent primates, rodents, boa constrictors, and cichlid fishes from Africa to South America sometime in the Oligocene.
In the early Miocene, after 22 mya, many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Because the fossils at 20 mya include fragments attributed to Victoriapithecus, the earliest cercopithecoid, the other forms are (by default) grouped as hominoids, without clear evidence as to which are closest to living apes and humans.
Among the presently recognised genera in this group, which ranges up to 13 mya, we find Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa.
The presence of other generalised non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene.
The youngest of the Miocene hominoids, Oreopithecus, is from 9 mya coal beds in Italy.
Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) became distinct between 18 and 12 Ma, and that of orangutans (subfamily Ponginae) at about 12 Ma; we have no fossils that clearly document the ancestry of gibbons, which may have originated in a so far unknown South East Asian hominid population, but fossil proto-orangutans may be represented by Ramapithecus from India and Griphopithecus from Turkey, dated to around 10 Ma.
It has been suggested that species close to last common ancestors of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece.
Molecular evidence suggests that between 8 and 4 mya, first the gorillas, and then the chimpanzee (genus Pan) split off from the line leading to the humans; human DNA is 98.4 percent identical to the DNA of chimpanzees. We have no fossil record, however, of either group of African great apes, possibly because bones do not fossilize in rain forest environments.
Hominines, however, seem to have been one of the mammal groups (as well as antelopes, hyenas, dogs, pigs, elephants, and horses) that adapted to the open grasslands as soon as this biome appeared, due to increasingly seasonal climates, about 8 mya, and their fossils are relatively well known.
The earliest are Sahelanthropus tchadensis (7- 6 mya) and Orrorin tugenensis (6 mya), followed by:
1. Ardipithecus (5.5-4.4 mya), with species Ar. kadabba and Ar. Ramidus.
2. Australopithecus (4-2 mya), with species Au. anamensis, Au. afarensis, Au. africanus, Au. bahrelghazali, and Au. Garhi.
3. Kenyanthropus (3-2.7 mya), with species Kenyanthropus platyops.
4. Paranthropus (3-1.2 mya), with species P. aethiopicus, P. boisei, and P. robustus.
5. Homo (2 mya-present), with species Homo habilis, Homo rudolfensis, Homo ergaster, Homo georgicus, Homo antecessor, Homo cepranensis, Homo erectus, Homo heidelbergensis, Homo rhodesiensis, Homo sapiens neanderthalensis, Homo sapiens idaltu, Archaic Homo sapiens, Homo floresiensis.
Essay # 4. Genus of Homo:
The word homo is Latin for “human”, chosen originally by Carolus Linnaeus in his classification system. It is often translated as “man”, although this can lead to confusion, given that the English word “man” can be generic like homo, but can also specifically refer to males. Latin for “man” in the gender-specific sense is vir (pronounced weer), cognate with “virile” and “werewolf”. The word “human” is from humanus, the adjectival form of homo.
In modern taxonomy, Homo sapiens are the only extant species of its genus, Homo. Likewise, the ongoing study of the origins of Homo sapiens often demonstrates that there were other Homo species, all of which are now extinct. While some of these other species might have been ancestors of H. sapiens, many were likely our “cousins”, having speciated away from our ancestral line.
There is not yet a consensus as to which of these groups should count as separate species and which as subspecies of another species. In some cases this is due to the paucity of fossils, in other cases it is due to the slight differences used to classify species in the Homo genus. The Sahara pump theory provides an explanation of the early variation in the genus Homo.
i. Homo Habilis:
H. habilis lived from about 2.4 to 1.4 million years ago (mya). H. habilis, the first species of the genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5-2 mya, when it diverged from the Australopithecines.
H. habilis had smaller molars and larger brains than the Australopithecines, and made tools from stone and perhaps animal bones. One of the first known hominids, it was nicknamed ‘handy man’ by its discoverer, Louis Leakey. Some scientists have proposed moving this species out of Homo and into Australopithecus.
ii. Homo Rudolfensis and Homo Georgicus:
These are proposed species names for fossils from about 1.9 -1.6 mya, the relation of which with H. habilis is not yet clear. H. rudolfensis refers to a single, incomplete skull from Kenya. Scientists have suggested that this was just another habilis, but this has not been confirmed.
H. georgicus, from Georgia, may be an intermediate form between H. habilis and H. erectus, or a sub-species of H. erectus.
iii. Homo Ergaster and Homo Erectus:
The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally gave the material the name Pithecanthropus erectus based on its morphology that he considered to be intermediate between that of humans and apes.
H. erectus lived from about 1.8 mya to 70,000 years ago. Often the early phase, from 1.8 to 1.25 mya, is considered to be a separate species, H. ergaster, or it is seen as a subspecies of erectus, Homo erectus ergaster.
In the Early Pleistocene, 1.5-1 mya, in Africa, Asia, and Europe, presumably, Homo habilis evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, H. erectus. In addition H. erectus was the first human ancestor to walk truly upright.
This was made possible by the evolution of locking knees and a different location of the foramen magnum (the hole in the skull where the spine enters). They may have used fire to cook their meat.
A famous example of Homo erectus is Peking Man; others were found in Asia (notably in Indonesia), Africa, and Europe. Many paleoanthropologists are now using the term Homo ergaster for the non-Asian forms of this group, and reserving H. erectus only for those fossils found in the Asian region and meeting certain skeletal and dental requirements which differ slightly from ergaster.
iv. Homo Cepranensis and Homo Antecessor:
These are proposed as species that may be intermediate between H. erectus and H. heidelbergensis.
H. cepranensis refers to a single skull cap from Italy, estimated to be about 800,000 years old.
H. antecessor is known from fossils from Spain and England that are 800,000-500,000 years old.
v. Homo Heidelbergensis:
H. heidelbergensis (Heidelberg Man) lived from about 800,000 to about 300,000 years ago. Also proposed as Homo sapiens heidelbergensis or Homo sapiens paleohungaricus.
vi. Homo Neanderthalensis:
H. neanderthalensis lived from about 250,000 to as recent as 30,000 years ago. Also proposed as Homo sapiens neanderthalensis- there is ongoing debate over whether the ‘Neanderthal Man’ was a separate species, Homo neanderthalensis, or a subspecies of H. sapiens.
While the debate remains unsettled, evidence from mitochondrial DNA and Y-chromosomal DNA sequencing indicates that little or no gene flow occurred between H. neanderthalensis and H. sapiens, and, therefore, the two were separate species.
vii. Homo Rhodesiensis, and the Gawis Cranium:
H. rhodesiensis, estimated to be 300,000-125,000 years old, most current experts believe Rhodesian Man to be within the group of Homo heidelbergensis though other designations such as Archaic Homo sapiens and Homo sapiens rhodesiensis have also been proposed.
In February 2006 a fossil, the Gawis cranium, was found which might possibly be a species intermediate between H. erectus and H. sapiens or one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is believed to be 500,000-250,000 years old.
Only summary details are known, and no peer reviewed studies have been released by the finding team. Gawis man’s facial features suggest its being either an intermediate species or an example of a “Bodo man” female.
viii. Homo Sapiens:
H. sapiens (“sapiens” means wise or intelligent) has lived from about 250,000 years ago to the present. Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in cranial expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens.
The direct evidence suggests that there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa (there is little evidence that this speciation occurred elsewhere). Then a subsequent migration within and out of Africa eventually replaced the earlier dispersed H. erectus.
This migration and origin theory is usually referred to as the single- origin theory. However, the current evidence does not preclude multiregional speciation, either. This is a hotly debated area in paleoanthropology.
Current research has established that human beings are genetically highly homogenous, that is the DNA of individuals is more alike than usual for most species, which may have resulted from their relatively recent evolution or the Toba catastrophe. Distinctive genetic characteristics have arisen, however, primarily as the result of small groups of people moving into new environmental circumstances.
These adapted traits are a very small component of the Homo sapiens genome and include such outward “racial” characteristics as skin color and nose form in addition to internal characteristics such as the ability to breathe more efficiently in high altitudes.
H. sapiens idaltu, from Ethiopia, lived from about 160,000 years ago (proposed subspecies). It is the oldest known anatomically modern human.
ix. Homo Floresiensis:
H. floresiensis, which lived about 100,000-12,000 years ago has been nicknamed hobbit for its small size, possibly a result of insular dwarfism. H. floresiensis is intriguing both for its size and its age, being a concrete example of a recent species of the genus Homo that exhibits derived traits not shared with modern humans.
In other words, H. floresiensis share a common ancestor with modern humans, but split from the modern human lineage and followed a distinct evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximately 18,000 years old. Her brain size was only 380 cm3 (which can be considered small even for a chimpanzee). She was only 1 meter in height.
However, there is an ongoing debate over whether H. floresiensis is indeed a separate species. Some scientists presently believe that H. floresiensis was a modern H. sapiens suffering from pathological dwarfism.
Use of Tools:
Using tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution—most notably the continued expansion of the human brain. Paleontology has yet to explain the expansion of this organ over millions of years despite being extremely demanding in terms of energy consumption.
The brain of a modern human consumes about 20 Watts (400 kilocalories per day), which is one fifth of the energy consumption of a human body. Increased tool use would allow for hunting and consuming meat, which is more energy-rich than plants. Researchers have suggested that early hominids were thus under evolutionary pressure to increase their capacity to create and use tools.
Precisely when early humans started to use tools is difficult to determine, because the more primitive these tools are (for example, sharp-edged stones) the more difficult it is to decide whether they are natural objects or human artifacts.
Stone Tools:
Stone tools are first attested around 2.6 million years ago, when H. habilis in Eastern Africa used so-called pebble tools, choppers made out of round pebbles that had been split by simple strikes.
This marks the beginning of the Paleolithic, or Old Stone Age; its end is taken to be the end of the last Ice Age, around 10,000 years ago. The Paleolithic is subdivided into the Lower Paleolithic (Early Stone Age, ending around 350,000-300,000 years ago), the Middle Paleolithic (Middle Stone Age, until 50,000-30,000 years ago), and the Upper Paleolithic.
The period from 700,000-300,000 years ago is also known as the Acheulean, when H. ergaster (or erectus) made large stone hand-axes out of flint and quartzite, at first quite rough (Early Acheulian), later “retouched” by additional, more subtle strikes at the sides of the flakes.
After 350,000 BP (Before Present) the more refined so-called Levallois technique was developed. It consisted of a series of consecutive strikes, by which scrapers, slicers (“racloirs”), needles, and flattened needles were made. Finally, after about 50,000 BP, ever more refined and specialised flint tools were made by the Neanderthals and the immigrant Cro-Magnons (knives, blades, skimmers). In this period they also started to make tools out of bone.
Essay # 5. Evolution of Neanderthals:
Archaic H. sapiens lived from 500,000 to 30,000 years ago and combined features of H. sapiens with those of H. erectus. The Neanderthals, considered in this group, lived in Europe and western Asia between 100,000 and 30,000 years ago before their disappearance.
Neanderthals were larger-brained than modern humans, had a sloping forehead, prominent brow ridges and a receding chin. They had a very prominent nose and ranged in height from 5 foot 2 inches (average female) to 5 foot 6 inches (average male).
Despite their image as brutish simpletons, Neanderthals were the first humans to bury their dead with artifacts, indicating abstract thought, perhaps a belief in an after-life. They lived in free-standing settlements, as well as caves. Neanderthal tools were more sophisticated than H. erectus’ tools, employing handles to gain extra leverage.
Did Neanderthals evolve gradually into modern humans, or were they replaced by modern forms originating from a single population? The answer to that depends on the answer to the question of the origin of H. sapiens from H. erectus. The out-of-Africa hypothesis suggests Neanderthals were a separate species (H. neandertalensis) replaced as modern humans (H. sapiens) spread from Africa. The regional continuity hypothesis suggests Neanderthals were a subspecies (H. sapiens neandertalensis) that evolved into modern humans (H. sapiens sapiens).
Agriculture and Migrations:
Since the evolution of H. erectus, migrations have been a fact of human existence, helping to spread genetic diversity as well as technological innovation. The most recent innovations have not been physical, but rather cultural.
The Neolithic transition, about 10,000 years ago, involved the change from hunter-gatherer societies to agricultural ones based on cultivation of plants and domesticated animals. Evidence suggests this began in the Middle East and spread outward via migrations. Genetic studies suggest agriculture spread by the migration of farmers into hunter-gatherer societies. This would produce a genetic blurring as the farmers interbred with the indigenous peoples, a pattern supported by genetics.
Most anthropologists agree that the New World was populated by a series of three migrations over the temporary land connection between Asia and North America. The Immigrants spread southward, eventually reaching Tierra del Fuego in the southernmost part of South America.
Anthropological and linguistic studies find three groups of peoples:
1. The Amerinds, who spread across North and South America.
2. The Na-Denes, who occupied the northwestern region of North America.
ADVERTISEMENTS:
3. The Eskaleuts, Eskimo and Aleut peoples who live in the far north.
Mitochondrial DNA studies find four distinct groups descended from peoples of Siberia. Amerind mtDNA suggests two waves of migration (one perhaps as old as 21-42 thousand years ago). The genetic model confirms the accepted ideas about human migration into the Americas and suggests a possible fourth wave.
Essay # 6. Models of Human Evolution:
Today, all humans are classified as belonging to the species Homo sapiens sapiens. However, this is not the first species of hominids- the first species of genus Homo, Homo habilis evolved in East Africa at least 2 million years ago, and members of this species populated different parts of Africa in a relatively short time.
Homo erectus evolved more than 1.8 million years ago, and by 1.5 million years ago had spread throughout the Old World. Virtually all physical anthropologists agree that Homo sapiens evolved out of Homo erectus.
Anthropologists have been divided as to whether Homo sapiens evolved as one interconnected species from H. erectus (called the Multiregional Model, or the Regional Continuity Model), or evolved only in East Africa, and then migrated out of Africa and replaced H. erectus populations throughout the Old World (called the Out of Africa Model or the Complete Replacement Model).
Anthropologists continue to debate both possibilities, and the evidence is technically ambiguous as to which model is correct, although most anthropologists currently favor the Out of Africa model.
Multiregional Model:
Advocates of the Multiregional model, primarily Milford Wolpoff and his followers, have argued that the simultaneous evolution of H. sapiens in different parts of Europe and Asia would have been possible if there was a degree of gene flow between archaic populations.
Similarities of morphological features between archaic European and Chinese populations and modern H. sapiens from the same regions, Wolpoff argues, support a regional continuity only possible within the Multiregional model. Wolpoff and others further argue that this model is consistent with clonal patterns of phenotypic variation.
Out of Africa Model:
According to the Out of Africa Model, developed by Christopher Stringer and Peter Andrews, modern H. sapiens evolved in Africa 200,000 years ago. Homo sapiens began migrating from Africa between 70,000 – 50,000 years ago and would eventually replace existing hominid species in Europe and Asia.
The Out of Africa Model has gained support by recent research using mitochondrial DNA (mtDNA). After analysing genealogy trees constructed using 133 types of mtDNA, they concluded that all were descended from a woman from Africa, dubbed Mitochondrial Eve.
A variation on this model involves the Southern dispersal theory, which has gained support in recent years from genetic, linguistic and archaeological evidence. In this theory, there was a coastal dispersal of modern humans from the Horn of Africa around 70,000 years ago. This group helped to populate Southeast Asia and Oceania, explaining the discovery of early human sites in these areas much earlier than those in the Levant.
A second wave of humans dispersed across the Sinai peninsula into Asia, resulting in the bulk of human population for Eurasia. This second group possessed a more sophisticated tool technology and was less dependent on coastal food sources than the original group. Much of the evidence for the first group’s expansion would have been destroyed by the rising sea levels at the end of the Holocene era.
