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Human evolution is the part of the theory of Evolution by which Human Beings emerged as a distinct Species . It is the subject of a broad Scientific Inquiry that seeks to understand and describe how this change and development occurred. The study of human evolution encompasses many scientific disciplines, most notably Physical Anthropology and Genetics . The term 'human', in the context of human evolution, refers to the genus '' Homo '', but studies of human evolution usually include other Hominin s, such as the Australopithecines . HISTORY OF PALEOANTHROPOLOGY The modern field of Paleoanthropology began with the discovery of ' Neanderthal man' (the eponymous skeleton was found in 1856, but there had been finds elsewhere since 1830); and evidence of other ' Cave Men ' in the 19th Century . The idea that humans are similar to certain Great Ape s had been obvious to people for some time, but the idea of the biological evolution of species in general was not legitimized until after Charles Darwin published '' On The Origin Of Species '' in 1859 . Though Darwin's first book on evolution did not address the specific question of human evolution— "light will be thrown on the origin of man and his history," was all Darwin wrote on the subject— the implications of evolutionary theory were clear to contemporary readers. Debates between Thomas Huxley and Richard Owen focused on the idea of human evolution, and by the time Darwin published his own book on the subject, '' Descent Of Man '', it was already a well-known interpretation of his theory— and the interpretation which made the theory highly controversial. Even many of Darwin's original supporters (such as Alfred Russel Wallace and Charles Lyell ) balked at the idea that human beings could have evolved their apparently boundless mental capacities and moral sensibilities through Natural Selection . Since the time of Carolus Linnaeus , the great apes were considered the closest relatives of human beings, based on morphological similarity. In the 19th century, it was speculated that our closest living relatives were Chimpanzee s and Gorilla s, and based on the natural range of these creatures, it was surmised humans share a Common Ancestor with Africa n apes and that fossils of these ancestors would ultimately be found in Africa. It was not until the 1920s that fossils other than ''neanderthalensis'' were discovered. In 1924 , Raymond Dart described '' Australopithecus Africanus ''. The Type Specimen was the Taung Child , an Australopithecine infant discovered in Taung , South Africa . The remains were a remarkably well-preserved tiny skull and an Endocranial Cast of the individual's brain. Although the brain was small (410 cm³), its shape was rounded, unlike that of chimpanzees and gorillas, and more like a modern human brain. Also, the specimen exhibited short Canine Teeth , and the position of the Foramen Magnum was evidence of Bipedal locomotion. All of these traits convinced Dart that the Taung baby was a bipedal human ancestor, a transitional form between apes and humans. Another 20 years would pass before Dart's claims were taken seriously, following the discovery of more fossils that resembled his find. The prevailing view of the time was that a large brain evolved before bipedality. It was thought that intelligence on par with modern humans was a prerequisite to bipedalism. The australopithecines are now thought to be the immediate ancestors of the genus ''Homo'', the group to which modern humans belong. Both australopithecines and ''Homo sapiens'' are part of the tribe Hominini , but recent data has brought into doubt the position of ''A. africanus'' as a direct ancestor of modern humans; it may well have been a dead-end cousin. The australopithecines were originally classified as either Gracile or Robust . The robust variety of ''Australopithecus'' has since been reclassified as '' Paranthropus ''. In the 1930s , when the robust specimens were first described, the ''Paranthropus'' genus was used. During the 1960s , the robust variety was moved into ''Australopithecus''. The recent trend has been back to the original classification as a separate genus. BEFORE ''HOMO'' The evolutionary history of the primates can be traced back for some 60 million years. Up until 35 million years ago (MYA), there were only small, Lemur - and Monkey -like primates. At about 35 MYA we also find larger, Ape -like animals, the beginnings of the Catarrhini speciation. Over the past 35 million years the catarrhine family tree shows half a dozen major bifurcations. Branching point dates can be inferred from fossil remains datings, or from analyses of DNA differences that have accumulated over time between primate groups existing today. Around 6 million years ago some of the Hominoid s started to walk upright, as is clear from both anatomical changes and fossilized tracks of their footsteps. Having their hands free apparently created opportunities for further development: they came to use increasingly clever tools, and developed progressively larger brains (increasing from 500 to 1400 cm³ over the past 3 milllion years). The latest of this group are modern humans, ''Homo sapiens sapiens''.
THE ''HOMO'' GENUS In modern taxonomy, ''Homo sapiens'' is 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 word ''homo'' is Latin for 'person', 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'', Cognate with "''vir''ile" and "''wer''ewolf". The word 'human' is from ''humanus'', the adjectival form of ''homo''. ''Homo habilis'' '' H. Habilis '' lived from about 2.4 to 1.5 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 Brain s 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 ''. ''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.
''Homo ergaster'' and ''Homo erectus'' '' 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. ''Homo cepranensis'' and ''Homo antecessor'' These are proposed as species that may be intermediate between ''H. erectus'' and ''H. heidelbergensis''.
''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''. ''Homo neanderthalensis'' ''l DNA extracted from Neanderthal bone] indicate that Neanderthals did not contribute mitochondrial DNA to modern humans… Neanderthals are not our ancestors." Subsequent investigation of a second source of Neanderthal DNA confirmed these findings. However, supporters of the Multiregional Hypothesis point to recent studies indicating non-African nuclear DNA heritage dating to one MYA, as well as apparent hybrid fossils found in Portugal and elsewhere, in rebuttal to the prevailing view. ''Homo rhodesiensis'', and the Gawis cranium
''Homo sapiens'' '' H. Sapiens '' ("sapiens" means wise or intelligent) has lived from about 200 TYA 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 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''. However, the current evidence does not ''preclude'' multiregional speciation, either. This is a hotly debated area in Paleoanthropology . Current research establishes that human beings are highly genetically homogenous, meaning that the DNA of individual ''Homo sapiens'' is more alike than usual for most species, a result of our relatively recent evolution. Distinctive genetic characteristics have arisen however, primarily as the result of small groups of people moving into new environmental circumstances. Such small groups are initially highly inbred, allowing the relatively rapid transmission of traits favorable to the new environment. 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 TYA (proposed subspecies). It is the oldest known anatomically modern human. ''Homo floresiensis'' '' H. Floresiensis '', which lived about 100-12 TYA (announced 28 October 2004 in the science journal '' Nature ''), has been nicknamed '' Hobbit '' for its small size, probably a result of Island Dwarfing . ''H. floresiensis'' is intriguing both for its size and its age, being by far the most recent species of Homo that does not lie along the direct evolutionary path of modern humans. The main find was a fossil believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximatly 18,000 years old. Her brain size was only 380 cm³ (which can be considered small even for a chimp). She was only 1 meter in height. Comparative table of ''Homo'' species USE OF TOOLS Using tools is not only a sign of intelligence, it also may have acted as a stimulant for human evolution. Over the past 3 or 2 million years, human brain size has increased threefold. A brain needs much energy: the brain of modern man uses about 20 Watt s, one fifth of total human energy consumption. Early hominoids, like apes, were essentially plant eaters (fruit, leaves, roots), their diet only occasionally supplemented by meat (often from scavenging). However, plant food in general yields considerably less energy and nutritive value than meat. Therefore, being able to hunt for large animals, which was only possible by using tools such as spears, made it possible for humans to sustain larger and more complex brains, which in turn allowed them to develop yet more intelligent and efficient tools. Precisely when early man 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. There is some evidence that the australopithecines (4 MYA) may have used broken bones as tools, but this is debated. Stone tools Stone tools are first attested around 2.6 million years ago, when ''H. habilis'' in Eastern Africa used so-called Pebble Tools , Chopper s 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 350–300 TYA), the Middle Paleolithic (Middle Stone Age, until 50–30 TYA), and the Upper Paleolithic . The period from 700–300 TYA is also known as the Acheulean , when ''H. ergaster'' (or ''erectus'') made large stone Hand-axe s out of Flint and Quartzite , at first quite rough (Early Acheulian), later " Retouch ed" by additional, more subtle strikes at the sides of the Flake s. After 350,000 BP (Before Present) the more refined so-called Levallois technique was developed. It consisted of 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 specialized 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. The "modern man" debate Until about 50,000–40,000 years ago the use of stone tools seems to have progressed stepwise: each phase (''habilis'', ''ergaster'', ''neanderthal'') started at a higher level than the previous one, but once that phase had started further development was slow. In other words, one might call these ''Homo'' species culturally conservative. After 50,000 BP human culture apparently started to change at much greater speed: 'modern' men started to bury their dead carefully, made clothing out of hides, developed sophisticated hunting techniques (such as pitfall traps, or driving animals to fall off cliffs), and made cave paintings. This speed-up of cultural change seems connected with the arrival of modern humans, ''homo sapiens sapiens''. Whether this was an acceleration from standstill, or a trend that had in fact already started earlier, is debated: many innovations of the past 50,000 years are known to have occasional precursors in the Middle Stone Age. Among innovations of the Acheulian and the Middle Stone Age are the use of fire (500,000 BP), building shelters (400,000 BP), production of stone blades or knives (280,000 BP), grinding stones (280,000 BP), long distance barter trade (140,000 BP), fishing gear (110,000 BP), mining (100,000 BP), and beads (75,000 BP). However, these mostly remain incidents and do not become common until after 50,000 BP. Theoretically, 'modern' human behaviour is taken to include four ingredient capabilities: abstract thinking (concepts free from specific examples), planning (taking steps to achieve a farther goal), innovation (finding new solutions), and symbolic behaviour (such as images, or rituals). Among concrete examples of modern human behaviour archologists include specialization of tools, use of jewelry and images (such as cave drawings), organization of living space, rituals (for example, burials with grave gifts), specialized hunting techniques, exploration of less hospitable geographical areas, and barter trade networks. Debate continues whether there was indeed a 'Revolution' leading to modern man ("the big bang of human consciousness"), or a more gradual evolution. What caused it is also debated. The cause might be genetic; in 2001 a language gene ( FoxP2 ) was found, that must have originated about 200,000 years ago; similar genes might have brought about 'modern man'. NOTABLE HUMAN EVOLUTION RESEARCHERS ADDITIONAL NOTES The validity of evolution and the origins of humanity have often been a subject of great political and religious controversy (see Creation-evolution Controversy and Hybrid-origin ). The classification of humans and their relatives has changed considerably over time (see History Of Hominoid Taxonomy ). Speculation about the future evolution of humans is often explored in Science Fiction as continued Speciation of humans as they fill various Ecological Niche s (see Adaptive Radiation and Co-evolution ). Currently, scientists estimate that humans branched off from their common ancestor with chimpanzees about 5-7 MYA. REFERENCES
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