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Biology

Physical characteristics

Main articles: human anatomy / human physical appearance / human height

In biology, humans are usually studied as one species among others, without special distinction. 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.

A human skeleton

The mean height of an American adult female is 162 cm (64 in) and the mean weight is 62 kg (137 lb). Males are typically larger: 175 cm (69 in) and 78 kilograms (172 lb). Humans vary substantially around these means, 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.

Human children, typically weighing 3-4 kilograms (6-9 pounds) and 50-60 centimetres (20-24 inches) in height, are born after a nine-month gestation period. 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.

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 [1] (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 about 120 years.

Humans may be the dominant species and have shown extremely high intelligence, but we also have our 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 (obesity can become common in areas where food is easily accessible). 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 and in remote, underdeveloped regions of our time, child-birth can be a dangerous ordeal for some women.

Mental characteristics

Humans consider themselves the most intelligent organism in the animal kingdom. Humans have the highest brain to bodymass 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 brainmass to bodymass ratio does give a good indication of relative intelligence. (Carl Sagan, The Dragons of Eden, 38)

The human ability to abstract is unparallelled in the animal kingdom. Human beings are only one of five species to have passed the mirror test of abstraction - the others being chimpanzees, orangutans, gorillas, 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.

Thinking, IQ, Memory, Invention, Science, Philosophy, Knowledge, Education, Consciousness

Habitats

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.

Humans' original life style is hunting/gathering, which is adapted to the savannah where they evolved. 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.

Population

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.

Humans living on Antarctica, under the ocean, or in space are part of scientific, military, or industrial expeditions, and habitation of these environments is expensive and typically limited in duration.

Life in space has thus far been sporadic, with up to ten humans in space at a given time (seven on the Space Shuttle, three on Mir) and currently around three in the International Space Station. This is a direct result of humans' vulnerability to ionizing radiation. Prior to 1961, all humans were restricted to the earth; Yuri Gagarin was the first human to travel into space. At various periods between 1969 and 1974, up to two humans spent varying amounts of time on the Moon. As of yet, residencies or human explorations on other planets have not come to be.

Origins

Main article: Human evolution

The closest surviving animal to humans is the chimpanzee; the second closest the gorilla and the third the orangutan. It is important to note, however, that humans only share a common ancestor population with these and are not descended directly from them. Biologists have compared a sequence of DNA base pairs between humans and chimpanzees, and estimated an overall genetic difference of less than 5% [2] (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 hominid 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.

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.

Humans compared to other species

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.

Biologists and scientists in general, though, do not consider "dominant" to be a useful term, because the adaptive value of any trait or complex of traits depends on the niche and is highly mutable. From a scientific standpoint, Homo sapiens certainly is among the most generalized species on Earth. Smaller and simpler organisms such as bacteria and insects greatly surpass humans in population size and diversity of species, but few single species occupy as many diverse environments as humans. Many other species, for example, are adapted to specific environments, whereas humans rely on the use of fire and on tools such as clothing and manufactured shelter, which are themselves often produced and used through complex social interactions.

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 (building shelter, weaving fabrics for clothing); the ability to alter the environment; language; and the development of complex social relationships and structures. Considered in isolation, however, these differences are not absolute, as ethologists have recorded such behaviors in many species. Apes and even birds, for example, are known to "fish" for insects using blades of grass or twigs, and even to shape the tools for that purpose. For these reasons, the idea that making and using tools is a defining characteristic of humans is often considered outdated, though of course no other animal uses tools to the same degree or with the same flexibility as Homo sapiens. Similarly, other animals often have methods of communication, but the degree to which humans create and use complex grammar and abstract concepts in language has not been seen in any other species.

Chomskian linguistics holds that a distinguishing feature of humans is that they are the only extant species with a language instinct - a genetic predisposition that produces a brain mechanism whose function is to acquire a language by observing those around us. Dolphins may also have this trait as they show dialect.

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. That is, humans can think abstractly about concepts and ideas. They can question, use logic, understand mathematical concepts, and so on in ways greater than other animals are known to do, although several species have demonstrated some abilities in these areas. In any case, the idea that these abilities distinguish humans from other species is the basis of the name Homo sapiens, Latin for 'wise man'. It should be noted, however, that the extinct species of the Homo genus (e.g. Homo neanderthalensis, Homo erectus) were also adept tool makers and there is some evidence that they may have had linguistic skills.

While humans have all these characteristics, from the biological viewpoint the question "What single characteristic distinguishes humans from all other animals?" is an odd one: it is not a question that is usually asked of cats, dolphins, or song sparrows. Finding other species that shape tools or can use sign language may shed light on human evolution, but it doesn't erase the differences or similarities between humans and other species.

References

• Jablonski, N.G. & Chaplin, G. The evolution of human skin coloration. Journal of Human Evolution 39 (2000) 57-106. [3] (http://www.bgsu.edu/departments/chem/faculty/leontis/chem447/PDF_files/Jablonski_skin_color_2000.pdf)

• Robins, A.H. (1991). Biological Perspectives on Human Pigmentation. Cambridge: Cambridge University Press. [4] (http://www.amazon.com/gp/reader/0521365147/ref=sib_rdr_fc/104-4483989-3863969?%5Fencoding=UTF8&p=S001#reader-link)

External links

• A Look at Modern Human Origins (http://www.modernhumanorigins.com/)
• Tree of Life (http://tolweb.org/tree?group=Homo_sapiens&contgroup=Homo)
• Wade, N. "Why Humans and Their Fur Parted Ways." (http://www.freerepublic.com/focus/f-news/966532/posts) New York Times (Science Times), 19 August 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.

Spirituality and Religion

While many humans believe that they are purely physical beings that can only be defined in biological and cultural terms, many others believe that humans also have a spirit or a soul. This section describes some of the ways in which humans have understood themselves from a spiritual point of view.

Animism

In aboriginal peoples, probably reflecting the state of early human society, religion and mythology are closely interwoven, with notions of animacy of many aspects of Nature, in many cases combined with ancestor worship. Shamans are humans gifted and trained in bridging the natural and the supernatural worlds.

Mysticism

Spiritual practices and experiences possibly, but not necessarily coupled with theism or religious institution have been present in all societies. Essentially mystic movements include the Vedanta, Yoga, early Buddhism (see also Human realm), the Eleusian cults, christian mystic orders and preachers such as Meister Eckhart, and islamic Sufism. They center on ineffable experience of, and unity with the supernatural (enlightenment).

Polytheism

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, continued in Hinduism, 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.

Monotheism

The idea of a single God that either incorporates or excels all lesser gods appeared independently in several cultures, possibly first in the heresy of Akhenaten (better referred to as Henotheism, a typical stage in the emergence of Monotheism). Concepts of good and evil in a moral sense arise as a consequence of a single God as absolute authority. In Judaism, God is central for having chosen the Hebrews as a people, and in the Old Testament 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), as well as in its expansiveness, leading to the long-standing rivalry between the two religions. Monotheistic religions have in common the belief that humanity was created by God, bound by filial duty, and cared for by paternal providence.

See also: God, Soul, Atman, Karma, Mystic, Ritual, Ecstasy (state), Sacrifice, Salvation, Resurrection, Incarnation, Reincarnation, Prayer, Worship, Morality, Conscience.

The Individual

Psyche and Consciousness

• Psychology

Emotions

• Love, Hate, Envy, Jealousy, Joy, Happiness

Sexuality

Body

• Human physical appearance
• Beauty, clothing, cosmetics, hairstyle, tattoos
• Health, Medicine

Birth and Death

Society

Language

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 and is often thought to have supernatural status or powers (see Magic, Mantra, Vac). The invention of writing systems some 5000 years ago, allowing the preservation of utterances, was a major step in cultural evolution. The science of Linguistics describes the structure of language, and the relation between different languages. There are estimated to be some 6000 different languages spoken today.

Families and Peer Groups

• Sociology

Tribes, Nations and States

• Anthropology
• History
• Political Science
• Economics
• Nationalism
• Ethnicity
• social class
• War

Culture and Civilization

• Agriculture
• Technology
• Art
• Science
• City
• Trade

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.

Prehistoric Times

Prehistoric notions about the status of humanity may be guessed by the etymology of ancient words for man. Latin homo (PIE *kþonyon) means "of the earth, earthling", probably in opposition to "celestial" beings. Greek ανθρωπος (mycenaean *anthrokwos) means "low-eyed", again probably contrasting with a divine perspective.

Ancient Orient

From the 3rd millennium Old Kingdom of Egypt, belief in the eternal afterlife of the human Ka is documented (anx anx an mit-k "Live life, not shalt thou die"). In the Old Testament, we make out a claim of dominance of humanity alongside radical pessimism because of the brevity of human life.

• Genesis 1:28: And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. (KJV)
• Ecclesiastes 1:2-3: Vanity of vanities, saith the Preacher, vanity of vanities; all is vanity. What profit hath a man of all his labour which he taketh under the sun? (KJV)

Classical Antiquity

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". Socrates gave the (doubtlessly tounge-in-cheek) definition of humans as "featherless bipeds" (Plato, Politicus). More serious is Aristotle's description of 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.

Middle Ages

The dominant world-view of medieval Europe, as dictated by the Catholic Church, was that human existence is characterized by sin, and that its aim should be to prepare for divine judgement after death. The 13th century pope Innocent III wrote about the essential misery of earthly existence in his "On the misery of the human condition". A view that was disputed by, for example, Gianozzo Manetti in his treatise "On human dignity".

Renaissance

A famous quote of Shakespeare's Hamlet (II, ii, 115-117), expressing the contrast of human physical beauty, intellectual faculty, and ephemereal nature:

What a piece of work is a man! How noble in reason! how infinite in faculties! in form and moving, how express and admirable! in action how like an angel! in apprehension, how like a god! the beauty of the world! the paragon of animals! And yet, to me, what is this quintessence of dust?

Modern Era

The Enlightenment was driven by a renewed conviction, that, in the words of Immanuel Kant, "Man is distinguished above all animals by his self-consciousness, by which he is a 'rational animal'". In the 19th century, Karl Marx defined man as "labouring animal" (animal laborans) in conscious opposition to this tradition. In the early 20th century, Sigmund Freud dealt a serious blow to positivism by postulating that the human self is divided in Ego, Superego and Id, and human behaviour to a large part controlled by the unconscious mind.

See also

• human behavior
• human biology
• human ecology
• human evolution
• human variability
• human condition
• human nature
• environmentalism
• space and survival
• homo
• humanoid
• humanism
• humanitarian
• man & woman, child & baby
• personal life

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