Human Evolution

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Evolutionary Biology

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Human Evolution

Homo HabilisWhere Lived: Eastern and Southern AfricaWhen Lived: 2.4 million to 1.4 million years agoYear of Discovery: 1960Height: average 100 - 135 cmWeight: average 32 kgHomo habilis lived from about 2.8 to 1.4 Ma. Homo habilis evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–2 Ma, when it diverged from the australopithecines. Homo habilis had smaller molars and larger brains than the australopithecinea, and made tools from stone and perhaps animal bones. One of the first known hominids, it was nicknamed 'handy man' by discoverer Louis Leakey due to its association with stone tools. Some scientists have proposed moving this species out of Homo and into Australopithecus due to the morphology of its skeleton being more adapted to living on trees rather than to moving on two legs like Homo sapiens.In May 2010, a new species, Homo gautegensis was discovered in South Africa.

AustralopithecusWhere Lived: Eastern Africa (Ethiopia, Kenya, Tanzania)When Lived: Between about 3.85 and 2.95 million years agoYear of Discovery: 1974Height: Males: average 151 cmFemales: average 105 cmWeight: Males: average 42 kgFemales: average 29 kgThe Australopithecus genus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago. During this time period various forms of australopiths existed, including Australopithecus anamenis, Afarensis, Sediba, and Africanus. There is still some debate amongst academics whether certain African hominid species of this time, such as A. Robustus and A. Boisei, constitute members of the same genus; if so, they would be considered to be A. robust australopiths whilst the others would be considered A. gracile australopiths. However, if these species do indeed constitute their own genus, then they may be given their own name, the Paranthropus.- Australopithecus (4–1.8 Ma)- Kenyanthropus (3–2.7 Ma)- Paranthropus (3–1.2 Ma)

SivapithecusWhere lived: Woodlands of central AsiaWhen lived: 12.5 million to 8.5 million years agoYear of discovery: 1910Height: 1.5 meters Weight: 50-75 poundsSivapithecus is a genus of extinct primates. Fossil remains of animals now assigned to this genus, dated from 12.5 million to 8.5 million years old in the Miocene, have been found since the 19th century in the Siwalik Hills in the Indian Subcontinent. Any one of the species in this genus may have been the ancestor to the modern orangutans.Some early discoveries were given the separate names Ramapithecus (Rama's Ape) and Bramapithecus (Brahma's Ape), and were thought to be possible ancestors of humans. This view is no longer considered tenable.

DryopithecusWhere lived: Eastern AfircaWhen lived: Miocene periodYear of discovery: 1856Height: Males: average 1.2 m tallFemales: average 1 mWeight: Males: average 54 kgFemales: average 40 kgDryopithecus was a genus of apes that is known from Eastern Africa into Eurasia during the late Miocene period. The first species of Dryopithecus was discovered at the site of Saint-Gaudens, Haute-Garonne, France, in 1856. Other dryopithecids have been found in Hungary, Spain, and China.Dryopithecus was suspensory, had a large brain, and a delayed development, but, unlike the former, it had a gracile jaw with thinly enameled molars and suspensory forelimbs; Begun 2004 notes that the similarities and differences between them provides insight into the timing and palaeontolography of hominid origins and the phylogenetic divide between Asian and Afro-European great apes).

Darwin provided the basis of human evolution theory with thepublication of The Descent of Man and Selection in Relation to Sex (1871). Humans are mammals which means that they are subject to the same evolutionary mechanisms as all other living things.


Human beings belong to the Hominid family. - They are bipedal. Some groups of primates may have become bipedal when they were forced to stop living in trees because of climate change. Bipedalism resulted in changes to the cranium, pelvis, spine and limbs. - They have an upright position. This improved their sight which allowed them to see their prey and predators. It also freed their hands so they could use them for activities other than movement.

Genus Homo

Human evolution

The main characteristic that defines the Homo genus is the capacity to use tools and instruments. To be able to do this, they had to evolve hands with an opposable thumb that let them make precise movements. They also needed a sufficiently developed brain that was capable of sending orders to the muscles involved in this type of movement. The chronological appearance of species in the Homo genus was:- Homo habilis - Homo erectus - Homo sapiensHomo sapiens is the only extant species of its genus, Homo. While some other, extinct Homo species might have been ancestors of Homo 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. In some cases this is due to the dearth of fossils, in other cases it is due to the slight differences used to classify species in the Homo genus.Based on archeological and palaeontological evidence, it has been possible to infer, to some extent, the ancient dietary practices of various Homospecies and to study the role of diet in physical and behavioral evolution within Homo.

Homo ErectusWhere Lived: Northern, Eastern, and Southern Africa; Western Asia (Dmanisi, Republic of Georgia); East Asia (China and Indonesia).When Lived: Between about 1.89 million and 143,000 years agoYear of Discovery: 1891Height: Ranges from 145 - 185 cmWeight: Ranges from 40 - 68 kgThe first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally named the material Pithecanthropus erectus based on its morphology, which he considered to be intermediate between that of humans and apes. Homo Erectus lived from about 1.8 Ma to about 70,000 years ago (which would indicate that they were probably wiped out by the Toba catastrophe; however, Homo floresiensis survived it). Often the early phase, from 1.8 to 1.25 Ma, is considered to be a separate species, Homo ergaster, or it is seen as a subspecies of Homo erectus, Homo erectus ergaster.In the early Pleistocene, 1.5–1 Ma, in Africa some populations of Homo habilis are thought to have evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, Homo erectus. 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.

Homo SapiensWhere Lived: Evolved in Africa, now worldwideWhen Lived: About 200,000 years ago to presentH. sapiens (the adjective sapiens is Latin for "wise" or "intelligent") have 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 skull expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens. The direct evidence suggests there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa. 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 recent single origin or Out of Africa theory. Current evidence does not preclude some multiregional evolution or some admixture of the migrant H. sapiens with existing Homo populations. This is a hotly debated area of paleoanthropology.Current research has established that humans 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 possibility of a population bottleneck resulting from cataclysmic natural events such as 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, but include various characteristics such as skin color and nose form, in addition to internal characteristics such as the ability to breathe more efficiently at high altitudes.

Anatomical ChangesHuman evolution is characterized by a number of morphological, developmental, physiological, and behavioral changes that have taken place since the split between the last common ancestor of humans and chimpanzees. The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny (gestation and infancy), and decreased sexual dimorphism. The relationship between these changes is the subject of ongoing debate. Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus.BipedalismBipedalism is the basic adaption of the Hominin line and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominins. The earliest bipedal Hominin is considered to be either Sahelanthropus or Orrorin, with Ardipithecus, a full bipedal, coming somewhat later. The knuckle-walkers, the gorilla and chimpanzee, diverged around the same time, and either Sahelanthropus or Orrorin may be our last shared ancestor.The early bipedals eventually evolved into the australopithecines and later the genus Homo. There are several theories of the adaptation value of bipedalism. It is possible that bipedalism was favored because it freed up the hands for reaching and carrying food, saved energy during locomotion, enabled long distance running and hunting, enhanced field of vision and helped avoid hyperthermia by reducing the surface area exposed to direct sun; all this mainly for thriving in the new grassland type environment rather than the previous forest type. A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking.EncephalizationThe human species developed a much larger brain than that of other primates – typically 1,330 cm3 in modern humans, over twice the size of that of a chimpanzee or gorilla. The pattern of encephalization started with Homo habilis, which at approximately 600 cm3 had a brain slightly larger than that of chimpanzees, and continued with Homo erectus (800–1,100 cm3), reaching a maximum in Neanderthals with an average size of (1,200–1,900 cm3), larger even than Homo sapiens. The pattern of human postnatal brain growth differs from that of other apes (heterochrony) and allows for extended periods of social learning and language acquisition in juvenile humans. However, the differences between the structure of human brains and those of other apes may be even more significant than differences in size.The increase in volume over time has affected areas within the brain unequally – the temporal lobes, which contain centers for language processing, have increased disproportionately, as has the prefrontal cortex which has been related to complex decision-making and moderating social behavior. Encephalization has been tied to an increasing emphasis on meat in the diet, or with the development of cooking, and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex. The human brain was able to expand because of the changes in the morphology of smaller mandibles and mandible muscle attachments to the skull into allowing more room for the brain to grow.Sexual DimorphismThe reduced degree of sexual dimorphism is visible primarily in the reduction of the male canine tooth relative to other ape species (except gibbons) and reduced brow ridges and general robustness of males. Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans and bonobos are the only apes in which the female is fertile year round and in which no special signals of fertility are produced by the body (such as genital swelling during estrus).Nonetheless, humans retain a degree of sexual dimorphism in the distribution of body hair and subcutaneous fat, and in the overall size, males being around 15% larger than females. These changes taken together have been interpreted as a result of an increased emphasis on pair bonding as a possible solution to the requirement for increased parental investment due to the prolonged infancy of offspring.Other ChangesA number of other changes have also characterized the evolution of humans, among them an increased importance on vision rather than smell; a smaller gut; loss of body hair; evolution of sweat glands; a change in the shape of the dental arcade from being u-shaped to being parabolic; development of a chin (found in Homo sapiens alone), development of styloid processes; development of a descended larynx.

EvidenceThe evidence on which scientific accounts of human evolution is based comes from many fields of natural science. The main sources of knowledge about the evolutionary process has traditionally been the fossil record, but since the development of genetics beginning in the 1970s, DNA analysis has come to occupy a place of comparable importance. The studies of ontogeny, phylogeny and especially evolutionary developmental biology of both vertebrates and invertebrates offer considerable insight into the evolution of all life, including how humans evolved. The specific study of the origin and life of humans is anthropology, particularly paleoanthropology which focuses on the study of human prehistory.Evidence from molecular biologyThe closest living relatives of humans are bonobos and chimpanzees (both genus Pan) and gorillas (genus Gorilla). With the sequencing of both the human and chimpanzee genome, current estimates of the similarity between their DNA sequences range between 95% and 99%. By using the technique called the molecular clock which estimates the time required for the number of divergent mutations to accumulate between two lineages, the approximate date for the split between lineages can be calculated. The gibbons (family Hylobatidae) and orangutans (genus Pongo) were the first groups to split from the line leading to the humans, then gorillas followed by the chimpanzees and bonobos. The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch.Genetic evidence has also been employed to resolve the question of whether there was any gene flow between early modern humans and Neanderthals, and to enhance our understanding of the early human migration patterns and splitting dates. By comparing the parts of the genome that are not under natural selection and which therefore accumulate mutations at a fairly steady rate, it is possible to reconstruct a genetic tree incorporating the entire human species since the last shared ancestor.Each time a certain mutation (Single-nucleotide polymorphism) appears in an individual and is passed on to his or her descendants a haplogroup is formed including all of the descendants of the individual who will also carry that mutation. By comparing mitochondrial DNA which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve, must have lived around 200,000 years ago.Evidence from the fossil recordThere is little fossil evidence for the divergence of the gorilla, chimpanzee and hominin lineages. The earliest fossils that have been proposed as members of the hominin lineage are Sahelanthropus tchadensis dating from 7 million years ago, Orrorin tugenensis dating from 5.7 million years ago and Ardipithecus kadabba dating to 5.6 million years ago. Each of these have been argued to be a bipedal ancestor of later hominins but, in each case, the claims have been contested. It is also possible that one or more of these species are ancestors of another branch of African apes, or that they represent a shared ancestor between hominins and other apes.The question of the relationship between these early fossil species and the hominin lineage is still to be resolved. From these early species, the australopithecines arose around 4 million years ago and diverged into robust (also called Paranthropus) and gracile branches, one of which (possibly A. garhi) probably went on to become ancestors of the genus Homo. The australopithecine species that is best represented in the fossil record is Australopithecus afarensis with more than one hundred fossil individuals represented, found from Northern Ethiopia (such as the famous "Lucy"), to Kenya, and South Africa. Fossils of robust australopithecines such as A. robustus (or alternatively Paranthropus robustus) and A./P. boisei are particularly abundant in South Africa at sites such as Kromdraai and Swartkrans, and around Lake Turkana in Kenya.


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