Although some scientists equate the term "humans" with all members of the genus Homo, in common usage it generally refers to Homo sapiens, the only extant member. All other members of the genus Homo, which are now extinct, are known as archaic humans, and the term "modern human" is used to distinguish Homo sapiens from archaic humans. Anatomically modern humans emerged around 300,000 years ago in Africa, evolving from Homo heidelbergensis or a similar species. Migrating out of Africa, they gradually replaced and interbred with local populations of archaic humans. Multiple hypotheses for the extinction of archaic human species such as Neanderthals include competition, violence, interbreeding with Homo sapiens, or inability to adapt to climate change.

Genes and the environment influence human biological variation in visible characteristics, physiology, disease susceptibility, mental abilities, body size, and life span. Though humans vary in many traits (such as genetic predispositions and physical features), humans are among the least genetically diverse primates. Any two humans are at least 99% genetically similar. Humans are sexually dimorphic: generally, males have greater body strength and females have a higher body fat percentage. At puberty, humans develop secondary sex characteristics. Females are capable of pregnancy, usually between puberty, at around 12 years old, and menopause, around the age of 50.

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Humans have a large, highly developed, and complex prefrontal cortex, the region of the brain associated with higher cognition. Humans are highly intelligent and capable of episodic memory; they have flexible facial expressions, self-awareness, and a theory of mind. The human mind is capable of introspection, private thought, imagination, volition, and forming views on existence. This has allowed great technological advancements and complex tool development through complex reasoning and the transmission of knowledge to subsequent generations through language.

All modern humans are classified into the species Homo sapiens, coined by Carl Linnaeus in his 1735 work Systema Naturae.[2] The generic name "Homo" is a learned 18th-century derivation from Latin hom, which refers to humans of either sex.[3][4] The word human can refer to all members of the Homo genus.[5] The name "Homo sapiens" means 'wise man' or 'knowledgeable man'.[6] There is disagreement if certain extinct members of the genus, namely Neanderthals, should be included as a separate species of humans or as a subspecies of H. sapiens.[5]

Despite the fact that the word animal is colloquially used as an antonym for human,[9] and contrary to a common biological misconception, humans are animals.[10] The word person is often used interchangeably with human, but philosophical debate exists as to whether personhood applies to all humans or all sentient beings, and further if one can lose personhood (such as by going into a persistent vegetative state).[11]

Human evolution was not a simple linear or branched progression but involved interbreeding between related species.[35][36][37] Genomic research has shown that hybridization between substantially diverged lineages was common in human evolution.[38] DNA evidence suggests that several genes of Neanderthal origin are present among all non sub-Saharan-African populations, and Neanderthals and other hominins, such as Denisovans, may have contributed up to 6% of their genome to present-day non sub-Saharan-African humans.[35][39][40]

Human 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 hairlessness,[41] obligate bipedalism, increased brain size and decreased sexual dimorphism (neoteny). The relationship between all these changes is the subject of ongoing debate.[42]

Until about 12,000 years ago, all humans lived as hunter-gatherers.[43][44] The Neolithic Revolution (the invention of agriculture) first took place in Southwest Asia and spread through large parts of the Old World over the following millennia.[45] It also occurred independently in Mesoamerica (about 6,000 years ago),[46] China,[47][48] Papua New Guinea,[49] and the Sahel and West Savanna regions of Africa.[50][51][52]

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 and sedentary lifestyle led to the emergence of early civilizations.[53][54][55]

In the 5th century BCE, history started being recorded as a discipline, which provided a much clearer picture of life at the time.[74] Between the 8th and 6th century BCE, Europe entered the classical antiquity age, a period when ancient Greece and ancient Rome flourished.[75][76] Around this time other civilizations also came to prominence. The Maya civilization started to build cities and create complex calendars.[77][78] In Africa, the Kingdom of Aksum overtook the declining Kingdom of Kush and facilitated trade between India and the Mediterranean.[79] In West Asia, the Achaemenid Empire's system of centralized governance became the precursor to many later empires,[80] while the Gupta Empire in India and the Han dynasty in China have been described as golden ages in their respective regions.[81][82]

By using advanced tools and clothing, humans have been able to extend their tolerance to a wide variety of temperatures, humidities, and altitudes.[122][123] As a result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforest, arid desert, extremely cold arctic regions, and heavily polluted cities; in comparison, most other species are confined to a few geographical areas by their limited adaptability.[124] The human population is not, however, uniformly distributed on the Earth's surface, because the population density varies from one region to another, and large stretches of surface are almost completely uninhabited, like Antarctica and vast swathes of the ocean.[122][125] Most humans (61%) live in Asia; the remainder live in the Americas (14%), Africa (14%), Europe (11%), and Oceania (0.5%).[126]

Within the last century, humans have explored challenging environments such as Antarctica, the deep sea, and outer space.[127] Human habitation within these hostile environments is restrictive and expensive, typically limited in duration, and restricted to scientific, military, or industrial expeditions.[127] Humans have briefly visited the Moon and made their presence felt on other celestial bodies through human-made robotic spacecraft.[128][129][130] Since the early 20th century, there has been continuous human presence in Antarctica through research stations and, since 2000, in space through habitation on the International Space Station.[131]

In 2018, 4.2 billion humans (55%) lived in urban areas, up from 751 million in 1950.[141] The most urbanized regions are Northern America (82%), Latin America (81%), Europe (74%) and Oceania (68%), with Africa and Asia having nearly 90% of the world's 3.4 billion rural population.[141] Problems for humans living in cities include various forms of pollution and crime,[142] especially in inner city and suburban slums. Humans have had a dramatic effect on the environment. They are apex predators, being rarely preyed upon by other species.[143] Human population growth, industrialization, land development, overconsumption and combustion of fossil fuels have led to environmental destruction and pollution that significantly contributes to the ongoing mass extinction of other forms of life.[144][145]

Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology. The dental formula of humans is: 2.1.2.32.1.2.3. Humans have proportionately shorter palates and much smaller teeth than other primates. They are the only primates to have short, relatively flush canine teeth. Humans have characteristically crowded teeth, with gaps from lost teeth usually closing up quickly in young individuals. Humans are gradually losing their third molars, with some individuals having them congenitally absent.[146]

Humans share with chimpanzees a vestigial tail,[147] appendix, flexible shoulder joints, grasping fingers and opposable thumbs.[148] Humans also have a more barrel-shaped chests in contrast to the funnel shape of other apes, an adaptation for bipedal respiration.[149] Apart from bipedalism and brain size, humans differ from chimpanzees mostly in smelling, hearing and digesting proteins.[150] While humans have a density of hair follicles comparable to other apes, it is predominantly vellus hair, most of which is so short and wispy as to be practically invisible.[151][152] Humans have about 2 million sweat glands spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on the palm of the hand and on the soles of the feet.[153]

It is estimated that the worldwide average height for an adult human male is about 171 cm (5 ft 7 in), while the worldwide average height for adult human females is about 159 cm (5 ft 3 in).[154] Shrinkage of stature may begin in middle age in some individuals but tends to be typical in the extremely aged.[155] Throughout history, human populations have universally become taller, probably as a consequence of better nutrition, healthcare, and living conditions.[156] The average mass of an adult human is 59 kg (130 lb) for females and 77 kg (170 lb) for males.[157][158] Like many other conditions, body weight and body type are influenced by both genetic susceptibility and environment and varies greatly among individuals.[159][160]

Humans have a far faster and more accurate throw than other animals.[161] Humans are also among the best long-distance runners in the animal kingdom, but slower over short distances.[162][150] Humans' thinner body hair and more productive sweat glands help avoid heat exhaustion while running for long distances.[163] Compared to other apes, the human heart produces greater stroke volume and cardiac output and the aorta is proportionately larger.[164][165] 0852c4b9a8

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