- For other uses, see Human (disambiguation).
Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof.
Biologists classify human beings as Homo sapiens (Latin for knowing man), a primate species of mammal with a highly developed brain, belonging to the family of great apes, along with chimpanzees, bonobos, gorillas, and orangutans . Theologists describe human beings in spiritual terms, using various concepts of soul which, in religion, are understood in relation to divine powers or beings; in mythology, they are also often contrasted with other humanoid races.
Anthropologists define human beings by their use of language, their organisation in complex societies, and their development of technology, and especially by their ability to form groups and institutions for mutual support and assistance.
Juvenile males are known as boys and adult males as men. Juvenile females are known as girls and adult females as women. Human beings are commonly referred to individually as persons or people and collectively as man, mankind, humanity, or the human race, while humans is used both for the collective and for individuals.
Until the 20th century, the English word of Latin origin human was only used adjectivally ("pertaining to mankind"). Nominal use of human (plural humans) is short for human being, and has been deprecated by some conservative English usage commentators. As an adjective, human is used neutrally (as in human race) but human and especially humane may also emphasize positive aspects of human nature, and can be synonymous with benevolent (vs. inhuman; c. f. humanitarian).
Main articles: Human anatomy, Human physical appearance, Human height
In biology, humans are usually studied as one of many known species on Earth. The biological study of humans often extends to the psychological as well as the physical, but usually not to the spiritual or the religious. Biologically, humans are defined as hominids of the species Homo sapiens, of which the only extant subspecies is Homo sapiens sapiens. They are usually considered the only surviving species in the genus Homo. Humans exhibit fully bipedal locomotion. This leaves the forelimbs available for manipulating objects using opposable thumbs.
The rules of scientific classification require a description of an individual specimen of the species. In 1993, Robert Bakker formally described the skull of paleontologist Edward Drinker Cope in an attempt to make Cope the type specimen for Homo sapiens. Despite current requirements that the specimen be available to the describing scientist (Cope was born in 1840 and the scientist who described and published Homo sapiens, Carolus Linnaeus, did so in 1758), it is unclear as to the lack of validity of Bakker's publication and many consider Cope to be the type specimen.
Humans vary substantially around the mean height and mean weight, and the means themselves have varied depending on locality and historical factors. Although body size is highly heritable, it is also significantly influenced by environmental and cultural factors such as diet. The mean height of a North American adult female is 162 cm (64 in) and the mean weight is 62 kg (137 lb). North American adult males are typically larger: 175 cm (69 in) and 78 kilograms (172 lb).
Human children are born after a nine-month gestation period, with typically 3-4 kilograms (6-9 pounds) in weight and 50-60 centimetres (20-24 inches) in height. Helpless at birth, they continue to grow for some years, typically reaching sexual maturity at around 12-15 years of age. Boys continue growing for some time after this, often only reaching their maximum height around the age of 18. These values vary substantially too, depending on heritable, environmental and cultural factors.
Human skin color can range from almost black to pinkish white in different people. In general, people with ancestors from sunny regions have darker skin than people with ancestors from regions with less sunlight. (However, this is complicated by the fact that there are people whose ancestors come from both sunny and less-sunny regions; and these people may have skin colors across the spectrum.) On average, women have slightly lighter skin than men.
Human life expectancy at birth is approaching 80 years in wealthy nations, with the assistance of science and technology. The number of centenarians in the world was estimated  (http://www.sacbee.com/content/lifestyle/seniors/story/6745838p-7696920c.html) at about 50,000 in 2003. The maximum human life span is thought to be over 120 years.
Humans may have been extremely successful due to their high intelligence, but they also have their share of physical complications. Humans are prone to suffer from obesity more so than other primates. This is largely due to the fact that humans are capable of producing more body fat than their primate relatives. Because humans are strictly bipedal, the pelvis region and spinal column tends to get worn, creating locomotion difficulties in advanced old age. Also, human females suffer from relatively complicated child-births (painful labors lasting up to 24 hours are not uncommon). Before the 20th century, child-birth was a dangerous ordeal for some women, and it still is in remote, underdeveloped regions of the world.
Many humans consider themselves the most intelligent organism in the animal kingdom, though there is debate as to whether or not cetaceans such as dolphins may have comparable or even higher intelligence. Certainly, they are the only evident technologically advanced animal. Humans have the highest brain to body mass ratio of all large animals (Dolphins have the second highest; sharks have the highest for a fish; and octopuses have the highest for an invertebrate). While this is not an absolute measure (inasmuch as a minimum brain mass is necessary for certain "housekeeping" functions), the brain to body mass ratio is generally assumed to give a good indication of relative intelligence.
The human ability to abstract is unparallelled in the animal kingdom. Human beings are only one of four species to have passed the mirror test of abstraction - the others being chimpanzees, orangutans, and dolphins. Tests have shown that a full grown chimpanzee has approximately the same ability to abstract as a four-year-old human child.
Pattern recognition is another area for which human beings are mentally well-suited.
The mental ability of humans and their intelligence make them, according to Pascal, the most sad creatures of all animals. The ability to have feelings, such as sadness or happiness, distinguish them from the other organisms, even if this assertion can be hardly proved with animal tests. Humans' existence, according to most philosophers, configures itself as the search of happiness.
The subjective experience of an individual centers around its consciousness, self-awareness or mind, allowing it the perception of its own existence and of the passage of time. Consciousness gives rise to the perception of free will, although some believe that perfect free will is an illusion, either limited or eliminated by predestination or social or biological determinism. The human psyche extends beyond consciousness, encompassing the total of the individual's mental and emotional aspects. The science of psychology studies the human psyche, in particular the unconscious. The practice of psychoanalysis devised by Sigmund Freud attempts to reveal portions of the unconscious. Freud structures the human self into Ego, Superego and Id. Carl Gustav Jung introduced the notion of the collective unconscious and a process of individuation, casting doubt on the exact definability of the individual.
See also Thinking, IQ, Memory, Invention, Science, Philosophy, Psychology, Knowledge, Education
The conventional view of human evolution states that humans evolved in inland savanna environments in Africa. (see Human evolution, Vagina gentium, Environment of Evolutionary Adaptedness). Culturally transmitted technology has allowed humans to colonize all of the continents and adapt to all climates. Within the last few decades, humans have been able to temporarily inhabit Antarctica, the ocean depths, and space, although long-term habitation of these three environments is not yet economical. Humans, with a population of about six billion, are one of the most numerous mammals on Earth.
Most humans (61%) live in the Asian region. The vast majority of the remainder live in the Americas (14%), Africa (13%) and Europe (12%), with only 0.3% in Australia. See list of countries by population and list of countries by population density.
The original human life-style is hunting-gathering, which is adapted to the savannah, the suggested scene of human evolution. Other human life styles are nomadism (often linked to animal herding) and permanent settlements made possible by the development of agriculture. Humans have a great capacity for altering their habitats by various methods, such as agriculture, irrigation, urban planning and construction, and activities accessory to those, such as transportation and manufacturing goods.
Permanent human settlements are dependent on proximity to water and, depending on the lifestyle, other natural resources such as fertile land for growing crops and grazing livestock or, seasonally by populations of prey. With the advent of large-scale trade and transportation infrastructure, immediate proximity to these resources has become less necessary, and in many places these factors are no longer the driving force behind growth and decline of population.
Human habitation within closed ecological systems in hostile environments (Antarctica, outer space) is expensive and typically limited in duration, and restricted to scientific, military, or industrial expeditions. Life in space has been very sporadic, with a maximum of thirteen humans in space at any given time. This is a direct result of human vulnerability to ionizing radiation. Prior to Yuri Gagarin's space flight in 1961, all humans were confined to Earth. Between 1969 and 1974, up to two humans at a time spent brief intervals on the Moon. As of 2004, no other celestial body has been visited by human beings. As of 2004, there has been continuous human presence in space since the launch of the initial crew to inhabit the International Space Station, on October 31, 2000.
In the 200 years from 1800 to 2000, world population has increased from one to six billion. It is expected to crest at ca. ten billion during the 21st century. As of 2004, a sizable minority — around 2.5 of a total of 6.3 billion people — live in urban surroundings. Urbanisation is expected to rise drastically during the 21st century. Problems for humans in cities include various forms of pollution, crime and poverty, especially in inner city and suburban slums.
Main article: Human evolution
The closest surviving animals to humans are the two species of chimpanzee; the second closest are the gorillas and the third the orangutans. These four sets of species make up the great apes. It is important to note, however, that humans only share a common ancestor population with these and are not descended directly from any of them. Biologists have compared a sequence of DNA base pairs between humans and chimpanzees, and estimated an overall genetic difference of less than 5%  (http://www.pnas.org/cgi/content/abstract/99/21/13633). It has been estimated that the human lineage diverged from that of chimpanzees about 5 million years ago, and from gorillas about 8 million years ago. However, recent news reports of a hominine skull approximately 7 million years old already showing a divergence from the ape lineage strongly suggests an earlier divergence.
Human evolution is characterized by a number of important trends:
- expansion of the brain cavity and brain itself, which is typically about 1,400 cm³ in volume, well over twice that of a chimpanzee or gorilla. Some physical anthropologists argue that a reorganization of the structure of the brain is more important than cranial expansion itself.
- canine tooth reduction.
- bipedal locomotion
- descent of the larynx (which makes possible the production of the complex sound known as vocal language).
How these trends are related, in what ways they have been adaptive, and what their role is in the evolution of complex social organization and culture, are matters of ongoing debate among physical anthropologists.
During the 1990s, variations in human mitochondrial DNA were recognized as a valuable source to reconstruct the human "family tree" and to trace early human migrations. Based on these measurements, the latest common ancestors of modern humans are estimated to have lived some 150 millennia ago, and to have expanded beyond Africa less than 100.000 years ago. Australia was colonized relatively early, ca. 70.000 years ago, Europe ca. 40.000 years ago, and the Americas were first settled roughly 30.000 years ago, with a second colonization across the Pacific ca. 15.000 years ago (see Human migration).
Various religious groups have raised objections concerning the theory of humanity's evolution from a common ancestor with the other hominoids. This has resulted in some controversy. See creationism, argument from evolution, and intelligent design for opposing points of view.
Spirituality and religion
For many humans, spirituality and religion play a central role in life. Often in this context, the human is considered as a "human person" consisting of a body, mind, and also a spirit or a soul that often is purported to transcend the body itself and even death. It is similarly often said that this soul, rather than the physical brain, is the true locus of consciousness (though there is no debate that the brain has heavy influence upon consciousness). The existence of a human soul is not proven or even defined; the concept is accepted by some and rejected by others. Also, there is debate within religious organizations as to whether or not other animals also have souls; some believe they do, others believe souls are held exclusively by humans, and some believe in group souls held by the community of animals rather than the individual. This section details how human beings are defined in spiritual terms, as well as some of the ways that this definition is expressed through ritual and religion.
Animism is the belief that objects and ideas including animals, tools, and natural phenomena have or are expressions of living spirits. In some animistic worldviews found in hunter-gatherer cultures, the human being is often regarded as on a roughly equal basis with animals, plants, and natural forces. Therefore, it is morally imperative to treat these agents with respect. In this worldview, humans are considered a denizen, or part, of nature, rather than superior to or separate from it. In such societies, ritual is considered essential for survival, as it wins the favor of the spirits of one's source of food, shelter, and fertility and wards off malevolent spirits. In more elaborate animistic religions, such as Shinto, there is a greater sense of a special character to humans that sets them apart from the general run of animals and objects, while still retaining the necessity of ritual to ensure good luck, favorable harvests, and so on.
Most animistic belief systems hold that the spirit survives physical death. In some systems, the spirit is believed to pass to an easier world of abundant game or ever-ripe crops, while in other systems (e.g., the Navajo religion), the spirit remains on earth as a ghost, often malignant. Still other systems combine these two beliefs, holding that the soul must journey to the spirit world without becoming lost and thus wandering as a ghost. Funeral, mourning rituals and ancestor worship performed by those surviving the deceased are often considered necessary for the successful completion of this journey.
Rituals in animistic cultures are often performed by shamans or priests, who are usually seen as possessing spiritual powers greater than or outside of the normal human experience.
The practice of head shrinking as found in some cultures derives from an animistic belief that one's war enemies, if the spirit is not trapped within the head, can escape the body and, after the spirit transmigrates to another body, take the form of a predatory animal and exact revenge.
Spiritual practices and experiences possibly, but not necessarily coupled with theism or religious institution have been present in all societies. They center on ineffable experience of, and unity with the supernatural (see enlightenment, immanence). In monotheistic mysticisms, the mystical experience focuses upon unity with God. Essentially mystic movements include the Vedanta, Yoga, early Buddhism (see also Human realm), the Eleusian cults, Christian mystic orders and preachers such as Gregory Palamas and Meister Eckhart, and Islamic Sufism.
The concept of gods as supernatural or very powerful intelligent beings, mostly imagined as anthropomorphic or zoomorphic, that want to be worshipped and appeased by humans is present from the beginning of history, and possibly reflected in Stone Age artwork, as well. In historical times, sacrificial rites evolved into institutionalised pagan religions led by clergies (e. g. Vedic religion, (practice of clergies continued in Hinduism, which, however developed monotheistic theologies, such as monistic theism, Egyptian, Greek, Roman and Germanic paganism). In these religions, humans are mainly characterised by their inferiority to the gods, sometimes reflected in a hierarchical society ruled by dynasties that claim divine descent. In religions that believe in reincarnation, most notably Hinduism, there is no impermeable barrier between animals, humans and gods, as the soul may migrate across different species without losing its identity.
Monotheistic religions generally believe that a single God, who is either the only god in existence or who incorporates or excels all lesser gods, created humanity, which is now bound by filial and moral duty, and cared for by paternal providence. In all Abrahamic religions (Judaism, Christianity, and Islam), humans are lord, or steward, over the earth and all other creatures, a little lower than the angels (see Great Chain of Being), and uniquely having a moral conscience. In Judaism, God is central for having chosen the Hebrews as a people, and in the Hebrew Bible, the fate of the community and its relationship with God has clear precedence over the fate of individuals. Christianity grew out of Judaism by emphasizing the fate of the individual, especially after death, and the personal intervention of God by incarnation, i.e. by temporally becoming human himself. Islam, while rejecting the Christian belief in Trinity and divine incarnation, is similar to Christianity in seeing humans as the viceregents of God and the only incarnate beings capable of free will (or of sin) or acting contrary to their nature. Hinduism also later developed monotheistic theologies such as monistic theism, which is different from Western notions of monotheism.
Burial ceremonies are a typical characteristic of human societies, often inspired by beliefs in an afterlife. Institutions of inheritance or ancestor worship may extend an individual's presence beyond its physical lifespan (see immortality).
See also: God, Soul, Atman, Karma, Mystic, Ritual, Ecstasy (state), Sacrifice, Korban, Salvation, Resurrection, Incarnation, Reincarnation, Prayer, Worship, Morality, Conscience, Sin.
Although many species are social, forming groups based on genetic ties, self-protection, or shared food gathering and distribution, humans are distinguished by the variety and complexity of the institutions that they form both for individual and group survival and for the preservation and development of technology, knowledge, and belief. Group identity and acceptance can exert powerful influence on individual behaviour, yet humans are also unique in their ability to form and adapt to new groups. An individual will develop strong feelings of loyalty towards such groups.
Sociology is the science that describes the interaction of human beings, while cultural anthropology describes the different human societies.
The human individual is conditioned to develop a particularly strong attachment to a small group, typically including its closest biological relatives, mother, father and siblings.
A similarly strong attachment may be forged with a small group of equals, resulting in peer groups of individuals of similar age, typically of the size of ten to twenty individuals, possibly related to the optimal size of a hunting party. Group dynamics and peer pressure may substantially influence the behaviour of group members (see also Asch conformity experiments).
Larger groups of humans can be unified by notions of common ancestry (tribes, ethnicities) or common cultural or material interests (nations or states), often further divided into social classes and hiearchical structures. A tribe may consist of a few hundred individuals, while the largest modern states contain more than a billion. Violent conflicts between such larger groups are wars. Loyalty to a larger group of this type is called nationalism or patriotism. In the extreme, feelings of loyalty towards an institution or an authority can reach pathological extremes, leading to mass hysteria or fascism (see also Milgram experiment, Stanford prison experiment).
The faculty of speech is a defining feature of humanity, probably predating phylogenetic separation of the modern population (see Proto-World language, Origins of language). Language is central to the communication between humans. The Hebrew word for "animal" (behemah) means "mute", defining humans as the "speaking animal" (animal loquens). Language is central to the feeling of identity of any culture or ethnicity. The invention of writing systems some 5000 years ago, allowing the preservation of utterances, was a major step in cultural evolution. Language, especially written language, is often thought to have supernatural status or powers (see Magic, Mantra, Vac).
The science of Linguistics describes the structure of language, and the relation between different languages. There are estimated to be some 6000 different languages used today. Most of them are spoken languages; most of the remainder are Sign Languages.
In addition to providing definition to the human condition, religion can also serve as a means of influencing and transmitting cultural norms of world-view and acceptable behaviour. Spirituality and ritual often are forces which may either unite a particular group, or cause division between groups.
Main article: Human self-reflection.
Humanity has always taken great interest in itself. The human faculty of introspection, the urge of an individual to discover more about its essence, invariably leads to the inquiry about the human condition and the essence of the human kind as a whole. Such self-reflection is the basis of philosophy and is present from the earliest historical records. This very article, since it is written by humans, is itself unavoidably an example of such self-reflection.
Humans often consider themselves to be the dominant species on Earth, and the most advanced in intelligence and ability to manage their environment. This belief is especially strong in Western culture, and is derived in part from the biblical creation story in which Adam is explicitly given dominion over the Earth and all of its creatures. Alongside such claims of dominance we often find radical pessimism because of the frailty and brevity of human life (In the Hebrew Bible, for example, dominion of man is promised in Genesis 1:28, but the author of Ecclesiastes bewails the vanity of all human effort).
The Greek philosopher Protagoras has made the famous claim that "Man is the measure of all things; of what is, that it is; of what is not, that it is not". Aristotle describes man as the "communal animal" (ζωον πολιτικον), i. e. emphasizing society-building as a central trait of human nature, and "animal with sapience" (ζωον λογον εχων, animal rationale), a term that also inspired the species' taxonomy, Homo sapiens.
From a scientific viewpoint, Homo sapiens certainly is among the most generalized species on Earth, and few single species occupy as many diverse environments as humans. Various attempts have been made to identify a single behavioral characteristic that distinguishes humans from all other animals, e.g. the ability to make and use tools, the ability to alter the environment, language and the development of complex social structures. Some anthropologists think that these readily observable characteristics (tool-making and language) are based on less easily observable mental processes that might be unique among humans: the ability to think symbolically, in the abstract or logically. It is difficult, however, to arrive at a set of attributes that include all humans, and humans only, and the wish to find unique human characteristics is a matter of human self-reflection more than one of zoology.
- Sagan, Carl: "The Dragons of Eden", A Balantine Book, 1978, ISBN 0345346297
- Jablonski, N.G. & Chaplin, G. "The evolution of human skin coloration." Journal of Human Evolution 39 (2000) 57-106. (in pdf format (http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf))
- Robins, A.H. Biological Perspectives on Human Pigmentation (http://www.amazon.com/gp/reader/0521365147/ref=sib_rdr_fc/104-4483989-3863969?%5Fencoding=UTF8&p=S001#reader-link). Cambridge: Cambridge University Press, 1991.
- A Look at Modern Human Origins (http://www.modernhumanorigins.com/)
- Tree of Life (http://tolweb.org/tree?group=Homo_sapiens&contgroup=Homo)
- Nicholas Wade. "Why Humans and Their Fur Parted Ways (http://www.freerepublic.com/focus/f-news/966532/posts)." New York Times (Science Times), August 19, 2003. Summary of clues to the saga in which humans evolved to lose their hair and had to adjust, including turning from white skin to black skin, together with an estimation of the time at which humans invented clothing.
- W. Gitt. The Wonder of Man (http://clv.dyndns.info/pdf/255397.pdf). (1999) A book defending a Christian creationist view of human biology. (PDF, 9 MB)