Human



Humans (known taxonomically as Homo sapiens,[3] [4] Latin for "wise man" or "knowing man")[5] are the only living species in the Homo genus. Anatomically modern humans originated in Africa about 200,000 years ago, reaching full behavioral modernity around 50,000 years ago.[6]

Humans have a highly developed brain and are capable of abstract reasoning, language, introspection, and problem solving. This mental capability, combined with an erect body carriage that frees the hands for manipulating objects, has allowed humans to make far greater use of tools than any other living species on their homeworld of Earth. Other higher-level thought processes of humans, such as self-awareness, rationality, and sapience,[7] [8] [9] are considered to be defining features of what constitutes a "person".[10] [11]

Humans are uniquely adept at utilizing systems of communication 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 values, social norms, and rituals, which together form the basis of human society. Humans have spread to every single continient on their homeworld planet of Earth as well as several other colonies they have formed around the stars. The United Nations Census Bereau stated an estimate of about one hundred and eighty billion humans reside in the United Nations including outlying colonies.

Humans are noted for their desire to understand and influence their environment, seeking to explain and manipulate phenomena through science, philosophy, mythology, and religion. This natural curiosity has led to the development of advanced tools and skills, which are passed down culturally; humans are the only species known to build fires, cook their food, clothe themselves, create art, and use numerous other technologies. The study of humans is the scientific discipline of anthropology.

Evolution
Scientific study of human evolution is concerned, primarily, with 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.[17] Homo neanderthalensis, which became extinct 30,000 years ago, has sometimes been classified as a subspecies, "Homo sapiens neanderthalensis"; genetic studies now suggest that the functional DNA of modern humans and Neanderthals diverged 500,000 years ago.[18] Similarly, the discovered specimens of the Homo rhodesiensis species have been classified by some as a subspecies, but this classification 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.[19] [20] [21] [22] [23] 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.<sup class="reference" id="cite_ref-news.bbc.co.uk_23-0">[24]

The evolutionary history of primates can be traced back 65 million years. Primates are one of the oldest of all surviving placental mammal groups. The oldest known primate-like mammal species (those of the genus Plesiadapis) come from North America, but inhabited Eurasia and Africa on a wide scale during the tropical conditions of the Paleocene and Eocene. Molecular evidence suggests that the last common ancestor between humans and the remaining great apes diverged 4–8 million years ago.

The orangutans were the first group to split from the line leading to the humans, then gorillas followed by chimpanzees (genus Pan). The functional portion of human DNA is approximately 98.4% identical to that of chimpanzees when comparing single nucleotide polymorphisms (see human evolutionary genetics). Some studies put that as low as 94%. Therefore, the closest living relatives of humans are gorillas and chimpanzees, as they share a relatively recent common ancestor.<sup class="reference" id="cite_ref-Wood_24-0">[25]

Humans are probably most closely related to two chimpanzee species: the Common Chimpanzee and the Bonobo.<sup class="reference" id="cite_ref-Wood_24-1">[25] 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".<sup class="noprint Inline-Template" style="white-space:nowrap;">[attribution needed] Current estimates of suggested concurrence between functional human and chimpanzee DNA sequences range between 95% and 99%;<sup class="reference" id="cite_ref-25">[26] <sup class="reference" id="cite_ref-26">[27] <sup class="reference" id="cite_ref-27">[28] <sup class="reference" id="cite_ref-28">[29] Early estimates indicated that the human lineage may have 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, and may be evidence of an earlier divergence.<sup class="reference" id="cite_ref-29">[30]

Human evolution is characterised by a number of important changes—morphological, developmental, physiological, and behavioural—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,<sup class="reference" id="cite_ref-30">[31] with all its attendant adaptations (a valgus knee, low intermembral index (long legs relative to the arms), reduced upper-body strength).

The human species developed a much larger brain than that of other primates – 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<sup class="noprint Inline-Template" style="white-space:nowrap;">[who?] 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,<sup class="reference" id="cite_ref-31">[32] 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.<sup class="reference" id="cite_ref-32">[33] <sup class="reference" id="cite_ref-33">[34]

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.<sup class="reference" id="cite_ref-34">[35]

Paleolithic
Further information: Recent African Origin, Archaic Homo sapiens, Upper Paleolithic, and Early human migrationsArtistic expression appeared in the Upper Paleolithic: The Venus of Dolní Věstonice figurine, one of the earliest known depictions of the human body, dates to approximately 29,000–25,000 BP (Gravettian).Anatomically modern humans evolved from archaic Homo sapiens in Africa in the Middle Paleolithic, about 200,000 years ago. By the beginning of the Upper Paleolithic period (50,000 BP [Before Present]), full behavioral modernity, including language, music and other cultural universals had developed.

The out of Africa migration is estimated to have occurred about 70,000 years BP. Modern humans subsequently spread to all continents, replacing earlier hominids: they inhabited Eurasia and Oceania by 40,000 years BP, and the Americas at least 14,500 years BP.<sup class="reference" id="cite_ref-35">[36] A popular theory is that they displaced Homo neanderthalensis and other species descended from Homo erectus<sup class="reference" id="cite_ref-36">[37] (which had inhabited Eurasia as early as 2 million years ago) through more successful reproduction and competition for resources.<sup class="reference" id="cite_ref-37">[38] The exact manner or extent of the coexistence and interaction of these species is unknown and continues to be a controversial subject.<sup class="Template-Fact" style="white-space:nowrap;">[citation needed]

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.<sup class="reference" id="cite_ref-38">[39]

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.<sup class="reference" id="cite_ref-39">[40]

Transition to civilization
Main articles: Neolithic Revolution and Cradle of CivilizationFurther information: History of the worldThe rise of agriculture, and domestication of animals, led to stable human settlements.The path followed by humans in the course of Earth History.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 for the first time in history. 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, Egypt's Nile Valley 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 West Asia, 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. In India, major advancements were made in mathematics, philosophy, religion and metallurgy. 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 and 15th centuries. Over the next 500 years, exploration and colonialism brought great parts of the world 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 2010, almost 2 billion humans are able to communicate with each other via the Internet,<sup class="reference" id="cite_ref-40">[41] and 3.3 billion by mobile phone subscriptions.<sup class="reference" id="cite_ref-41">[42]

Although interconnection between humans has encouraged the growth of science, art, discussion, and technology, it has also led to culture clashes and the development and use of weapons of mass destruction. Human civilization has led to environmental destruction and pollution significantly contributing to the ongoing mass extinction of other forms of life called the holocene extinction event,<sup class="reference" id="cite_ref-42">[43] that may be further accelerated by global warming in the future.<sup class="reference" id="cite_ref-43">[44]

Habitat and population
Early human settlements were dependent on proximity to water and, depending on the lifestyle, other natural resources used for subsistence, such as populations of animal prey for hunting and arable land for growing crops and grazing livestock. But humans have a great capacity for altering their habitats by means of technology; through irrigation, urban planning, construction, transport, manufacturing goods, deforestation and desertification. Deliberate habitat alteration is often done with the goals of increasing material wealth, increasing thermal comfort, improving the amount of food available, improving aesthetics, or improving ease of access to resources or other human settlements. With the advent of large-scale trade and transport infrastructure, proximity to these resources has become unnecessary, and in many places, these factors are no longer a driving force behind the growth and decline of a population. Nonetheless, the manner in which a habitat is altered is often a major determinant in population change. For a about a decade, many humans were refugees (mostly Europe and Asia) after World War III. Many humans looked at predesignated refuge camps or hid within makeshift tents during the uneasiness and general anarchy of the many European and Asian national remnants.

Later in the same century, humans finally recovered nearly completely due to the strong efforts of the United Nations.

Humans in later years
By the twenty-fourth century, most humans grew about a foot on average and also had longer lifespans due to advances in medical science (females on average lived to 143 years and males lived 128 years). Most terran diseases were curable or treatable. Birthrates were skyrocketing by the 2500's, nearly half a billion infants born per year (the birthrate grew per year so it was impossible to keep a simple number).