human evolution

 

theory of the origins of the human species, Homo sapiens. Modern understanding of human origins is derived largely from the findings of paleontology, anthropology, and genetics, and involves the process of natural selection (see Darwinism). Although gaps in the fossil record due to differential preservation prevent the complete specification of the line of human descent, H. sapiens share clear anatomical, genetic, and historic relationships to other primates. Of all primates, humans bear particularly close affinity to other members of a group known as hominoids, or apes, which includes orangutans, gibbons, gorillas, chimpanzees, and humans. Humans and their immediate ancestors, known as hominids, are notable among hominoids for their bipedal locomotion, slow rate of maturation, large brain size, and, at least among the more recent hominids, the development of a relatively sophisticated capacity for language, tool use, and social activity.

The Evolutionary Tree

Humans are mammals of the Primate order. The earliest primates evolved about 65 million years ago in the geological period known as the Paleocene epoch. They were small-brained, arboreal fruit eaters, similar to modern tree shrews. Primates of the Eocene epoch (55 to 38 million years ago) were similar and ancestral to contemporary tarsiers, lemurs, and tree shrews, and are classified as lower primates or prosimians. During the late Eocene, the higher primates, or anthropoids, developed from prosimian ancestors and, aided by continental drift, diverged into New World (or platyrrhine) and Old World (or catarrhine) monkeys. The branching of Old World monkeys and hominoids apparently occurred in the late Oligocene (38 to 25 million years ago) or early Miocene (25 to 8 million years ago), a time period poorly represented in the fossil record. The lesser apes (gibbons and siamangs) and other hominoid lines diverged about 20 million years ago, while the Asian great apes (the orangutan being the only surviving form) diverged from the African hominoids about 15 to 10 million years ago. Genetic evidence suggests that the ancestral lines of gorillas diverged about 8 million years ago and that chimpanzees and hominids diverged about 5 million years ago.

Hominid Evolution

The earliest known hominids are members of the genus Australopithecus, the earliest of which date to more than 4 million years ago. Unlike other primates, but like all hominids, australopithecines were bipedal. Their crania, however, were small and apelike, with an average cranial capacity of about 450 cc in the gracile species and 600 cc in the robust forms. Australopithecines that have been considered ancestral in the lineage leading to the human genus Homo include A. afarensis (an important skeleton of which is popularly known as Lucy) and A. africanus. The exact position of these and other early species on the hominid family tree continues to be disputed.

The first member of the genus Homo, a small gracile species known as H. habilis, was present in east Africa at least 2 million years ago. H. habilis was the first hominid to exhibit the marked expansion of the brain (with an average cranial capacity of about 750 cc) that would become a hallmark of subsequent hominid evolutionary history. By about 1.6 million years ago, H. habilis had evolved into a larger, more robust, and larger-brained species known as Homo erectus. Cranial capacities ranged from about 900 cc in early specimens to 1050 cc in later ones. H. erectus persisted for well over a million years and migrated off the African continent into Asia, Indonesia, and Europe.

Between 500,000 and 250,000 years ago, H. erectus evolved into H. sapiens. Transitional forms between H. erectus and H. sapiens are referred to as archaic H. sapiens. With the exception of H. sapiens neandertalensis (see Neanderthal man), no additional subspecies are recognized. Indeed, some scientists consider Neanderthal a separate species. Archaic H. sapiens changed gradually, becoming somewhat larger, more gracile and larger-brained through time. Cranial capacity, for example, increased from about 1150 cc in early transitional forms to the current world average of just over 1350 cc. By 150,000 years ago in Africa and Asia and 28,000 years ago in Europe (see Cro-Magnon man), the transition to H. sapiens was complete, and fully modern humans became the single surviving hominid species.

The Evolution of Culture

Among hominids, a parallel evolutionary process involving increased intelligence and cultural complexity is apparent in the material record. Evidence of greater behavioral flexibility and adaptability presumably reflects the decreased influence of genetically encoded behaviors and the increased importance of learning and social interaction in transmitting and maintaining behavioral adaptations (see culture). Because the organization of neural circuitry is more significant than overall cranial capacity in establishing mental capabilities, direct inferences from the fossil record are likely to be misleading. Contemporary humans, for example, exhibit considerable variability in cranial capacity (1150 cc to 1600 cc), none of which is related to intelligence.

Tool use was once thought to be the hallmark of members of the genus Homo, beginning with H. habilis, but is now known to be common among chimpanzees. The earliest stone tools of the lower Paleolithic, known as Oldowan tools and dating to about 2 to 2.5 million years ago, were once thought to have been manufactured by H. habilis. Recent finds suggest that Oldowan tools may also have been made by robust australopithecines. The simultaneous emergence of H. erectus and the more complex Achuelian tool tradition may indicate shifting adaptations as much as increased intelligence.

While it is clear that H. erectus was much more versatile than any of its predecessors, adapting its technologies and behaviors to diverse environmental conditions, the extent and limitations of its intellectual endowment remain a subject of heated debate. This is also the case for both archaic H. sapiens and Neanderthals, the latter associated with the more sophisticated technologies of the middle Paleolithic. However impressive the achievements of H. erectus and early H. sapiens, most material remains predating 40,000 years ago reflect utilitarian concerns. Nonetheless, there is now scattered African archaeological evidence from before that time (in one case as early as 90,000 years ago) of the production by H. sapiens of beads and other decorative work, perhaps indicating a gradual development of the aesthetic concerns and other symbolic thinking characteristic of later human societies. Whether the emergence of modern H. sapiens corresponds to the explosion of technological innovations and artistic activities associated with Cro-Magnon culture or was a more prolonged process of development is a subject of archaeological debate.

Bibliography

See R. Lewin, Human Evolution (2d ed. 1989) and, with R. Leakey, Origins Reconsidered (1992); I. Tattersall, The Fossil Trail: How We Know What We Think We Know about Human Evolution (1995); A. Walker and P. Shipman, The Wisdom of the Bones: In Search of Human Origins (1996); C. Stringer and R. McKie, African Exodus: The Origins of Modern Humanity (1997); L. R. Berger and B. Hilton-Barber, In the Footsteps of Eve: The Mystery of Human Origins (2000); I. Tattersall and J. H. Schwartz, Extinct Humans (2000).

Human evolution is the part of biological evolution concerning the emergence of humans as a distinct species from other apes. 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, linguistics and genetics. The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually include other hominins, such as the australopithecines.

History of paleoanthropology

Paleoanthropology is the study of ancient humans based on fossil evidence, tools, and other signs of human habitation. The modern field of paleoanthropology began in the 19th century with the discovery of "Neanderthal man". The eponymous skeleton was found in 1856, but there had been finds elsewhere since 1830.

By 1859, the morphological similarity of humans to certain great apes had been discussed and argued for some time, but the idea of the biological evolution of species in general was not legitimized until Charles Darwin published On the Origin of Species in November of that year. 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. Nevertheless, the implications of evolutionary theory were clear to contemporary readers.^[1]

Debates between Thomas Huxley and Richard Owen focused on human evolution. Huxley convincingly illustrated many of the similarities and differences between humans and apes in his 1863 book Evidence as to Man's Place in Nature. By the time Darwin published his own book on the subject, The 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 impressive mental capacities and moral sensibilities through natural selection.

Since the time of Carolus Linnaeus, scientists have considered the great apes to be the closest relatives of human beings, based on morphological similarity. In the 19th century, they speculated that the closest living relatives of humans are chimpanzees and gorillas. Based on the natural range of these creatures, they surmised that humans share a common ancestor with other African apes and that fossils of these ancestors would ultimately be found in Africa.

It was not until the 1920s that hominid fossils were discovered in Africa. In 1924, Raymond Dart described Australopithecus africanus.^[2] The type specimen was the Taung Child, an australopithecine infant discovered in a cave deposit being mined for concrete at 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 immediate ancestors of the genus Homo, the group to which modern humans belong.^[3] 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.^[4] The australopithecines were originally classified as either gracile or robust. The robust variety of Australopithecus has since been reclassified as Paranthropus, although it is still regarded as a subgenus of Australopithecus by some authors.^[5]

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 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. 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.^[6] It suggests that the great ape and human lineage 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. Begun says that the great apes 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 Ma (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 recognized 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 generalized 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.

Molecular evidence further 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:

• Ardipithecus (5.5–4.4 mya), with species Ar. kadabba and Ar. ramidus;
• Australopithecus (4–2 mya), with species Au. anamensis, Au. afarensis, Au. africanus, Au. bahrelghazali, and Au. garhi;
• Kenyanthropus (3-2.7 mya), with species Kenyanthropus platyops
• Paranthropus (3–1.2 mya), with species P. aethiopicus, P. boisei, and P. robustus;
• Homo (2 mya–present), with species Homo habilis, Homo rudolfensis, Homo ergaster, Homo georgicus erectus, Homo antecessor, Homo cepranensis, Homo erectus, Homo heidelbergensis, Homo rhodesiensis, Homo sapiens neanderthalensis, Homo sapiens idaltu, Archaic Homo sapiens, Homo floresiensis

The genus 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, cognate with "virile" and "werewolf". The word "human" is from humanus, the adjectival form of homo.

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.^[7] 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.

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.

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.^[8]
• H. georgicus, from Georgia, may be an intermediate form between H. habilis and H. erectus,^[9] or a sub-species of H. erectus.^[10]

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.^[11] 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.^[12] 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.^{[citation needed]}

• H. cepranensis refers to a single skull cap from Italy, estimated to be about 800,000 years old.^[13]
• H. antecessor is known from fossils from Spain and England that are 800,000–500,000 years old.^[14]

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.^[15]

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.^[16] 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.^[17] In 1997, Dr. Mark Stoneking, then an associate professor of anthropology at Pennsylvania State University, stated: "These results [based on mitochondrial 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 supported these findings.^[18] However, supporters of the multiregional hypothesis point to recent studies indicating non-African nuclear DNA heritage dating to one mya,^[19] although the reliability of these studies have been questioned.^[20]

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 and an example of a "Bodo man" female.^[21]

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 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. 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 160,000 years ago (proposed subspecies). It is the oldest known anatomically modern human.

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 (island) dwarfism.^[22] 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.^[23] Some scientists presently believe that H. floresiensis was a modern H. sapiens suffering from pathological dwarfism.^[24] This hypothesis is supported in part, because the modern humans who live on Flores, the island where the skeleton was found, are pygmies. This coupled with pathological dwarfism could indeed create a hobbit-like human. The other major attack on H. floresiensis is that it was found with tools only associated with H. sapiens.^[24]

Comparative table of Homo species

Bolded species names indicate the existence of numerous fossil records.

Species	Lived when (mya)	Lived where	Adult length (m)	Adult weight (kg)	Brain volume (cm³)	Fossil record	Discovery / publication of name
H. habilis	2.5–1.4	East Africa	1.0–1.5	30–55	600	many	1960/1964
H. rudolfensis	1.9	Kenya				1 skull	1972/1986
H. georgicus	1.8–1.6	Georgia			600	few	1999/2002
H. ergaster	1.9–1.25	East and Southern Africa	1.9		700–850	many	1975
H. erectus	2–0.3	Africa, Eurasia (Java, China, Vietnam, Caucasus)	1.8	60	900–1100	many	1891/1892
H. cepranensis	0.8	Italy				1 skull cap	1994/2003
H. antecessor	0.8–0.35	Spain, England	1.75	90	1000	3 sites	1994/1997
H. heidelbergensis	0.6–0.25	Europe, Africa	1.8	60	1100–1400	many	1907/1908
H. rhodesiensis	0.3–0.12	Zambia			1300	very few	1921
H. neanderthalensis	0.23–0.024	Europe, West Asia	1.6	55–70 (heavily built)	1200–1700	many	1829/1864
H. sapiens sapiens	0.25–present	worldwide	1.4–1.9	55–80	1000–1850	still living	—/1758
H. sapiens idaltu	0.16	Ethiopia			1450	3 craniums	1997/2003
H. floresiensis	0.10–0.012	Indonesia	1.0	25	400	7 individuals	2003/2004

Use of tools

Using tools is not only a sign of intelligence, it also may have acted as a stimulus for human evolution. Over the past 3 or 2 million years, human brain size has increased threefold. A brain needs a lot of energy: the brain of a modern human consumes about 20 Watts (400 kilocalories per day); this is 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 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. 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, choppers made out of round pebbles that had been split by simple strikes.^[25] 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.^[25] This speed-up of cultural change seems connected with the arrival of modern humans, homo sapiens. As human culture advanced, different populations of humans began to create novelty in existing technologies. Artifacts such as fish hooks, buttons and bone needles begin to show signs of variation among different population of humans, something that had not been seen in human cultures prior to 50,000 BP. Typically, neanderthalensis populations are found with technology similar to other contemporary neanderthalensis populations.

Theoretically, modern human behavior 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, anthropologists 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 humans ("the big bang of human consciousness"), or a more gradual evolution.^[26]

Notable human evolution researchers

• James Burnett, Lord Monboddo, a British judge most famous today as a founder of modern comparative historical linguistics
• Charles Darwin, a British naturalist who documented considerable evidence that species originate through evolutionary change
• Richard Dawkins, a British ethologist, evolutionary biologist who has promoted a gene-centered view of evolution
• J. B. S. Haldane, a British geneticist and evolutionary biologist
• Henry McHenry, an American anthropologist who specializes in studies of human evolution, the origins of bipedality, and paleoanthropology
• Louis Leakey, an African archaeologist and naturalist whose work was important in establishing human evolutionary development in Africa
• Richard Leakey, an African paleontologist and archaeologist, son of Louis Leakey
• Svante Pääbo, a Swedish biologist specializing in evolutionary genetics
• Jeffrey H. Schwartz, an American physical anthropologist and professor of biological anthropology
• Leonard Shlain, an American surgeon and author of three books
• Erik Trinkaus, a prominent American paleoanthropologist and expert on Neanderthal biology and human evolution
• Milford H. Wolpoff, an American paleoanthropologist who leading proponent of the multiregional evolution hypothesis
• Sir Alister Hardy, a British zoologist, who first hypothesised the aquatic ape theory of human evolution

Species list

This list will conduct in chronological order, following genus.

• Sahelanthropus
  • Sahelanthropus tchadensis
• Orrorin
  • Orrorin tugenensis
• Ardipithecus
  • Ardipithecus kadabba
  • Ardipithecus ramidus
• Australopithecus
  • Australopithecus anamensis
  • Australopithecus afarensis
  • Australopithecus bahrelghazali
  • Australopithecus africanus
  • Australopithecus garhi
• Paranthropus
  • Paranthropus aethiopicus
  • Paranthropus boisei
  • Paranthropus robustus
• Kenyanthropus
  • Kenyanthropus platyops
• Homo
  • Homo habilis
  • Homo rudolfensis
  • Homo ergaster
  • Homo georgicus
  • Homo erectus
  • Homo cepranensis
  • Homo antecessor
  • Homo heidelbergensis
  • Homo rhodesiensis
  • Homo neanderthalensis
  • Homo sapiens idaltu
  • Homo sapiens (Cro-magnon)
  • Homo sapiens sapiens
  • Homo floresiensis

Additional notes

• The validity of evolution and the origins of humanity have often been a subject of great political and religious controversy within the non-scientific community (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 niches (see Adaptive radiation and Co-evolution), as well as deliberate self-modification (see Participant evolution).
• Currently, scientists have estimated that humans branched off from their common ancestor with chimpanzees about 5–7 mya.

References