Human

A human is a member of a species of bipedal primates in the family Hominidae (taxonomically Homo sapiens—Latin: "wise man" or "knowing man"). DNA and fossil evidence indicates that modern humans originated in east Africa about 200,000 years ago. When compared to other animals and primates, humans have a highly developed brain, capable of abstract reasoning, language, introspection and problem solving. This mental capability, combined with an erect body carriage that frees the forelimbs (arms) for manipulating objects, has allowed humans to make far greater use of tools than any other species. Humans are distributed worldwide, with significant populations inhabiting most land areas of Earth, as well as large numbers of humans at any particular moment flying in vehicles through the atmosphere, many others traveling over and beneath the oceans, and even a few individuals living in low Earth orbit. The human population on Earth is greater than 6.7 billion, as of February 2009.

Like most higher primates, humans are social by nature. Humans are particularly adept at utilizing systems of communication—primarily spoken, gestural, and written language—for self-expression, the exchange of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families to nations. Social interactions between humans have established an extremely wide variety of traditions, rituals, ethics, values, social norms, and laws, which together form the basis of human society. Humans are distinctive as a species on the Earth by a sense of beauty and aesthetics at least in so far as this results in a material culture, which, combined with the desire for self-expression and proportionally a very large brain-size, has led to innovations such as art, written language, and science.

Humans seek to understand and influence the environment around them, trying to explain and manipulate natural phenomena through philosophy, art, science, mythology, and religion. This natural curiosity has led to the development of advanced tools and skills. Humans are the only species known to build fires, cook their food, and clothe themselves; as well as utilize numerous other technologies. Humans pass down their skills and knowledge to the next generations and so are regarded as dependent upon culture.

Name

The English adjective human is a Middle English loan from Old French humain, ultimately from Latin hūmānus, the adjective of homō "man". Use as a noun (with a plural humans) dates to the 16th century. The native English term man is now often reserved for male adults, but can still be used for "mankind" in general in Modern English. The word is from Proto-Germanic *mannaz, from a Proto-Indo-European(PIE) root *man-, cognate to Sanskrit manu-.

The generic name Homo is a learned 18th century derivation from Latin homō "man", ultimately "earthly being" (Old Latin hemō, cognate to Old English guma "man", from PIE *dʰǵʰ_emon-, meaning 'earth' or 'ground').

History

Origin

A reconstruction of Australopithecus afarensis, a human ancestor that had developed bipedalism, but which lacked the large brain of modern humans.

The scientific study of human evolution encompasses the development of the genus Homo, but usually involves studying other hominids and hominines as well, such as Australopithecus. "Modern humans" are defined as the Homo sapiens species, of which the only extant subspecies is known as Homo sapiens sapiens. Homo sapiens idaltu (roughly translated as "elder wise human"), the other known subspecies, is now extinct. Homo neanderthalensis, which became extinct 30,000 years ago, has sometimes been classified as a subspecies, "Homo sapiens neanderthalensis", but genetic studies now suggest a divergence of the Neanderthal species from Homo sapiens about 500,000 years ago. Similarly, the few specimens of Homo rhodesiensis have also occasionally been classified as a subspecies, but this is not widely accepted. Anatomically modern humans first appear in the fossil record in Africa about 195,000 years ago, and studies of molecular biology give evidence that the approximate time of divergence from the common ancestor of all modern human populations was 200,000 years ago. The broad study of African genetic diversity headed by Dr.Sarah Tishkoff found the San people to express the greatest genetic diversity among the 113 distinct populations sampled, making them one of 14 "ancestral population clusters".The research also located the origin of modern human migration in south-western Africa, near the coastal border of Namibia and Angola.

The closest living relatives of humans are gorillas and chimpanzees, but humans did not evolve from these apes: instead these apes share a common ancestor with modern humans. Humans are probably most closely related to two chimpanzee species: Common Chimpanzee and Bonobo. Full genome sequencing has resulted in the conclusion that "after 6.5 [million] years of separate evolution, the differences between chimpanzee and human are ten times greater than those between two unrelated people and ten times less than those between rats and mice". Suggested concurrence between human and chimpanzee DNA sequences range between 95% and 99%. It has been estimated that the human lineage diverged from that of chimpanzees about five million years ago, and from that of gorillas about eight million years ago. However, a hominid skull discovered in Chad in 2001, classified as Sahelanthropus tchadensis, is approximately seven million years old, which may indicate an earlier divergence.

Human evolution is characterized by a number of important morphological, developmental, physiological and behavioural changes, which have taken place since the split between the last common ancestor of humans and chimpanzees. The first major morphological change was the evolution of a bipedal locomotor adaptation from an arboreal or semi-arboreal one, with all its attendant adaptations, such as a valgus knee, low intermembral index (long legs relative to the arms), and reduced upper-body strength.

Later, ancestral humans developed a much larger brain – typically 1,400 cm³ in modern humans, over twice the size of that of a chimpanzee or gorilla. 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. Physical anthropologists argue that the differences between the structure of human brains and those of other apes are even more significant than their differences in size.

Other significant morphological changes included: the evolution of a power and precision grip; a reduced masticatory system; a reduction of the canine tooth; and the descent of the larynx and hyoid bone, making speech possible. An important physiological change in humans was the evolution of hidden oestrus, or concealed ovulation, which may have coincided with the evolution of important behavioural changes, such as pair bonding. Another significant behavioural change was the development of material culture, with human-made objects becoming increasingly common and diversified over time. The relationship between all these changes is the subject of ongoing debate.

The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years.

Paleolithic

Artistic expression appears in the Upper Paleolithic: The Venus of Dolní Věstonice figurine, one of the earliest known depictions of the human body, dated to approximately 29,000–25,000 years ago (Gravettian).

Homo sapiens appears about 200,000 BP (Before Present), in the Middle Paleolithic. Over the next 150,000 years, by the beginning of the Upper Paleolithic 50,000 years ago, full behavioral modernity, including language, music and other cultural universals develop. The out of Africa migration is estimated to have occurred about 70,000 years ago. Modern humans subsequently spread to all continents, replacing earlier hominids: they inhabited Eurasia and Oceania by 40,000 BP, and the Americas at least 14,500 years ago. They displaced Homo neanderthalensis and other species descended from Homo erectus (which had inhabited Eurasia as early as 2 million years ago) through more successful reproduction and competition for resources.

Evidence from archaeogenetics accumulating since the 1990s has lent strong support to the "out-of-Africa" scenario, and has marginalized the competing multiregional hypothesis, which proposed that modern humans evolved, at least in part, from independent hominid populations.

Geneticists Lynn Jorde and Henry Harpending of the University of Utah propose that the variation in human DNA is minute compared to that of other species. They also propose that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs – no more than 10,000, and possibly as few as 1,000 – resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, one being the Toba catastrophe theory.

Transition to civilization

The rise of agriculture, and domestication of animals, led to stable human settlements.

Until c. 10,000 years ago, most humans lived as hunter-gatherers. They generally lived in small nomadic groups known as band societies. The advent of agriculture prompted the Neolithic Revolution, when access to food surplus led to the formation of permanent human settlements, the domestication of animals and the use of metal tools. Agriculture encouraged trade and cooperation, and led to complex society. Because of the significance of this date for human society, it is the epoch of the Holocene calendar or Human Era.

About 6,000 years ago, the first proto-states developed in Mesopotamia, and in the Sahara/Nile and the Indus Valleys. Military forces were formed for protection, and government bureaucracies for administration. States cooperated and competed for resources, in some cases waging wars. Around 2,000–3,000 years ago, some states, such as Persia, India, China, Rome, and Greece, developed through conquest into the first expansive empires. Influential religions, such as Judaism, originating in the Middle East, and Hinduism, a religious tradition that originated in South Asia, also rose to prominence at this time.

The late Middle Ages saw the rise of revolutionary ideas and technologies. In China, an advanced and urbanized society promoted innovations and sciences, such as printing and seed drilling. The Islamic Golden Age saw major scientific advancements in Muslim empires. In Europe, the rediscovery of classical learning and inventions such as the printing press led to the Renaissance in the 14th century. Over the next 500 years, exploration and colonialism brought much of the Americas, Asia, and Africa under European control, leading to later struggles for independence. The Scientific Revolution in the 17th century and the Industrial Revolution in the 18th–19th centuries promoted major innovations in transport, such as the railway and automobile; energy development, such as coal and electricity; and government, such as representative democracy and Communism.

With the advent of the Information Age at the end of the 20th century, modern humans live in a world that has become increasingly globalized and interconnected. As of 2008, over 1.4 billion humans are connected to each other via the Internet, and 3.3 billion by mobile phone subscriptions.

Although interconnection between humans has encouraged the growth of science, art, discussion, and technology, it has also led to culture clashes, the development and use of weapons of mass destruction, and increased environmental destruction and pollution, affecting not only themselves but also most other life forms on the planet.