Homo sapiens idaltu (extinct)
Homo sapiens sapiens
Human beings define themselves in biological, social, and spiritual terms. Biologically, humans are classified as the species Homo sapiens (Latin for "knowing man"): a bipedal primate belonging to the superfamily of Hominoidea, with all of the apes: chimpanzees, gorillas, orangutans, and gibbons.
Humans have an erect body carriage that frees the upper limbs for manipulating objects, and a highly developed brain and consequent capacity for abstract reasoning, speech, language, and introspection.
Behaviorally, human beings are defined by their use of language; their organization into complex social structures composed of many cooperating and competing groups, nations, states, and institutions, distinguished by their different aims and ritual practices; and their development of complex technology. These behavioral differences have given rise to myriad cultures incorporating many forms of beliefs, myths, rituals, values, and social norms.
The self-consciousness of human beings, their resultant curious and introspective nature, and their dominance over other animals have given rise to attempts to explain the development and nature of the species, in both materialist and spiritual terms. The latter emphasizes a spiritual or non-physical dimension to life, and may include belief in God, gods or other supernatural entities, and reference to the concept of the soul. Such self-reflection is the basis of philosophy and is present in the earliest historical records.
In English, juvenile males are called boys, adult males men, juvenile females girls, and adult females women. Humans are commonly referred to as persons or people and collectively as man, mankind, humanity, or the human race. Until the 20th century, human was only used adjectivally ("pertaining to mankind"). Nominal use of human (plural humans) is short for human being, and used not to be considered good style in traditional English grammar. 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 (versus inhumane; c.f. humanitarian).
A distinction is maintained in philosophy and law between the notions "human being," or "man," and "person". The former refers to the species, while the latter refers to a rational agent: see, for example, John Locke's Essay concerning Human Understanding II 27 and Immanuel Kant's Introduction to the Metaphysic of Morals. The term "person" is thus used of non-human animals, and could be used of a mythical being, an artificial intelligence, or an extraterrestrial. An important question in theology and the philosophy of religion concerns whether God is a person. (See also Great ape personhood.)
In Latin, humanus is the adjectival form of the noun homo, translated as "man" (to include males and females). The Old English word man could also have this generic meaning, as demonstrated by such compounds as wifman (“female person”) → wiman → woman. For the etymology of man see mannaz.
The life of the individual begins at conception. An egg is usually fertilized inside the female by the male through sexual intercourse, though in vitro fertilization methods are also used. The developing individual is first called a zygote; as it grows through successive stages inside the female's uterus over a period of 38 weeks, it is called an embryo, then a fetus. At birth, the fully grown fetus, now called a baby, is expelled from the female's body and breathes independently for the first time, at which point the baby is recognized as a person entitled to the full protection of the law, though some jurisdictions extend personhood to human fetuses while they remain in the uterus. Human life ends with the individual's death.
Compared with that in other species, human childbirth is relatively complicated. Painful labors lasting up to twenty-four hours or more are not uncommon, and may result in injury to the child or the death of the mother, although the chances of a successful labor increased significantly during the twentieth century in wealthier countries. It remains an arguably more dangerous ordeal in remote, underdeveloped regions of the world, though the women who live in these regions have argued that their natural childbirth methods are safer and less traumatic for mother and child.
The prospect of death may cause unease or fear. (See also near death experience.) Burial ceremonies are characteristic of human societies, often inspired by beliefs in an afterlife. Institutions of inheritance or ancestor worship may extend an individual's presence beyond his physical lifespan (see immortality).
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, although some argue that the two species of chimpanzees should be reclassified from Pan troglodytes and Pan paniscus to Homo troglodytes and Homo paniscus, given their sharing a recent ancestor with man. Humans exhibit fully bipedal locomotion. This leaves the forelimbs available for manipulating objects using opposable thumbs.
Humans vary substantially around the mean height and mean weight, which vary depending on locality and historical factors. Although body size is largely determined by genes, it is also significantly influenced by diet and exercise. 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 12-15 years of age. Boys continue growing for some time after this, reaching their maximum height around the age of 18. These values vary too, depending on genes and environment.
Human skin color can range from very dark brown to very pale pink 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.
There are striking differences in life expectancy around the world. The developed world is quickly getting older, with the median age around 40 years (highest in Monaco at 45.1 years), while in the developing world, the median age is 15-20 years (the lowest in Uganda at 14.8 years). Life expectancy at birth is 77.2 years in the U.S. as of 2001.  The expected life span at birth in Singapore is 84.29 years for a female and 78.96 years for a male, while in Botswana, due largely to AIDS, it is 30.99 years for a male and 30.53 years for a female. One in five Europeans, but one in twenty Africans, is 60 years or older, according to The World Factbook. 
The number of centenarians in the world was estimated by the United Nations  at 210,000 in 2002. The maximum human life span is thought to be over 120 years. Worldwide, there are 81 men aged 60 or over for every 100 women, and among the oldest, there are 53 men for every 100 women.
Because humans are bipedal, the pelvic region and spinal column tend to get worn, creating locomotion difficulties in old age. Humans are also more likely than other primates to suffer from obesity because of poor diet and lack of exercise.
Main article: Genetics of humans
Humans are a eukaryotic species. A human has 46 chromosomes: (22 pairs of autosomes, and 2 sex chromosomes). At present estimate, humans have approximately 20,000-25,000 genes and share 98.5% of their DNA with their closest living evolutionary relatives, the common chimpanzee and the bonobo, or pygmy chimpanzee.  Humans have an XY sex determination system, so that females have the sex chromosomes XX and males have XY. The X chromosome is longer and carries many genes not on the Y chromosome, which means that defects of X-linked recessive genes affect men more often than women. For example, genes that control the clotting of blood reside on the X chromosome. Women have a blood-clotting gene on each X chromosome so that one normal blood-clotting gene can compensate for a flaw in the gene on the other X chromosome. But men are hemizygous for the blood-clotting gene since there is no gene on the Y chromosome to control blood clotting. As a result, men will suffer from hemophilia more often than women.
Many humans consider themselves as the most intelligent species in the animal kingdom. Certainly, humans are the only technologically advanced animal. Along with neural complexity, the brain-to-body-mass ratio is generally assumed to be a good indicator of relative intelligence. Humans have the second highest brain-to-body-mass ratio or encephalization quotient (EQ) of all animals, with the tree shrew having the highest  and the bottlenose dolphin very similar to humans. (Sharks have the highest for a fish; and octopi the highest for an invertebrate).
The human ability to abstract may be unparalleled in the animal kingdom. Human beings are one of four species to pass the mirror test — which tests whether an animal recognizes its reflection as an image of itself — along with chimpanzees or bonobos, orangutans, and dolphins. Human beings under the age of four usually fail the test.
Human emotion has a significant influence on, or can even be said to control, human behaviour. Emotional experiences perceived as pleasant, like love or joy, contrast with those perceived as unpleasant, like hate, envy, or jealousy.
Weariness — Nothing is so insufferable to man as to be completely at rest, without passions, without business, without diversion, without study. He then feels his nothingness, his forlornness, his insufficiency, his dependence, his weakness, his emptiness. There will immediately arise from the depth of his heart weariness, gloom, sadness, fretfulness, vexation, despair, (Pascal, 1669).
Human sexuality, besides ensuring reproduction, has important social functions, creating bonds and hierarchies among individuals. Sexual desire is experienced as a bodily urge, often accompanied by strong emotions, both positive (such as love or ecstasy) and negative (such as jealousy). (See also Libido.)
The physical appearance of the human body is central to culture and art. In every human culture, people adorn their bodies, with tattoos, cosmetics, clothing, and jewelry. Hairstyles and hair color also have important cultural implications. The perception of an individual as physically beautiful or ugly can have profound implications for their lives. This is particularly true of women, whose external appearance is highly valued in most, if not all, human societies.
The individual need for regular intake of food and drink is prominently reflected in human culture. (See also food science.) Failure to obtain food leads to hunger and eventually starvation, while failure to obtain water leads to dehydration and thirst. Both starvation and dehydration cause death if not alleviated: human beings can survive for over two months without food, but only up to around 14 days without water. (See also famine, malnutrition).
The average sleep requirement is between seven and eight hours a day for an adult and nine to ten hours for a child. Elderly people usually sleep for six to seven hours. It is common, however, in modern societies for people to get less sleep than they need. (See also sleep deprivation.)
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.) 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 explore Antarctica, the ocean depths, and space, although long-term habitation of these environments is not yet possible. 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 lifestyle is hunting-gathering, which is adapted to the savanna. Other human lifestyles 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, construction, transport, 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 transport infrastructure, immediate proximity to these resources has become unnecessary, 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, 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, in part because of human vulnerability to ionizing radiation, starting with Yuri Gagarin's space flight in 1961. 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, although there has been a continuous human presence in space since the launch of the initial crew to inhabit the International Space Station, on October 31, 2000.
From 1800 to 2000, the human population increased from one to six billion. It is expected to crest at around ten billion during the 21st century. As of 2004, around 2.5 out of 6.3 billion people live in urban centers, and this is expected to rise during the 21st century. Problems for humans living in cities include various forms of pollution, crime, and poverty, especially in inner city and suburban slums.
Geneticists Lynn Jorde and Henry Harpending of the University of Utah have concluded that the variation in the total stock of human DNA is minute compared to that of other species; and that around 74,000 years ago, human population was reduced to a small number of breeding pairs, possibly as small as 1000, resulting in a very small residual gene pool. Various reasons for this bottleneck have been postulated, the most popular being the eruption of a volcano called Toba. (See the Toba catastrophe theory.)
The faculty of speech may be 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), though non-human animals are now known to use language too, and non-human primates are able to learn human sign language   (pdf). Language can be central to the sense of identity that unites cultures and ethnicities.
The invention of writing systems some 5000 years ago, allowing the preservation of speech, was a major step in cultural evolution. Language, especially written language, is sometimes thought to have supernatural status or powers. (See Magic, Mantra, Vac.)
The science of linguistics describes the structure of language and the relationship between languages. There are estimated to be some 6,000 different languages used today. Most of them are spoken languages; the remainder are sign languages.
Main article: Human evolution
The closest surviving relatives of humans are chimpanzees, the second closest bonobos, the third orangutans. Together with gorillas, these four make up the category of great apes. Biologists have compared a sequence of DNA base pairs between humans and chimpanzees, and estimated an overall genetic difference of less than 1 per cent. It has been estimated that the human lineage diverged from that of chimpanzees about five million years ago, and from gorillas about eight million years ago. However, the discovery of a hominine skull approximately seven million years old already showing a divergence from the ape lineage suggests an earlier divergence.
Human evolution is characterized by a number of important trends :
How these trends are related and what their role is in the evolution of complex social organization and culture, are matters of ongoing debate.
During the 1990s, variations in human mitochondrial DNA were recognized as a valuable source for reconstructing the human "family tree" and for tracing early human migrations. As a result, the ancestors of all modern humans are thought to have evolved in Africa over 150,000 years ago; modern humans began to move out of Africa less than 100,000 years ago. Australia was colonized 70,000 years ago; Europe 40,000 years ago with later waves 22,000 and 9,000 years ago, according to Ornello Semino of the University of Pavia and Peter Underhill of Stanford University ; and the Americas 30,000 years ago, with a second colonization from across the Pacific Ocean 15,000 years ago. (See Human migration.)
Since the human embryo normally takes its mitochondrial DNA from its mother's egg and not from the sperm, variations in human mitochondrial DNA provide a means of identifying those individuals who share a common matrilineal ancestor. A mathematical analysis of mitochondrial DNA from thousands of living individuals suggests that the matrilineal lines for the people analyzed converges on one ancestor called Mitochondrial Eve (ME) who lived in Africa about 200,000 years ago. That is, ME is claimed to be the most-recent common ancestor of all humans alive today with respect to matrilineal descent (Boyd and Silk 2003:389-399).
Culture is defined here as a set of distinctive material, intellectual, emotional, and spiritual features of a social group, including art, literature, lifestyles, value systems, traditions, rituals, and beliefs.
One common understanding of culture is to see it as consisting of three elements: values, social norms, and artifacts. Values are ideas about what is important. Norms are expectations of how people ought to behave. Each human culture has different methods, often called laws and legal systems, of describing and enforcing its norms, though there are unwritten expectations and informal sanctions too. Artifacts – things, or material culture – derive from the culture's values and norms.
Scientists and philosophers largely agree that humans consist of a body alone (roughly the physicalist or reductionist view); or that they also have minds, the locus of, or another word for, consciousness (roughly the dualist position).
However, many people further believe that humans also have a soul or spirit that survives death; that is, they believe there is an afterlife. There is debate within religious organizations as to whether non-human animals can be said to have souls; some believe they do, while others believe that souls are exclusively human, or that there are group souls held by the community of animals. Others again, beginning with Thales of Miletus, believe that plants also have immortal souls. This section details various ways that humans are defined by religious groups, as well as some of the ways that the religious beliefs are ritually expressed.
In some animistic worldviews found in hunter-gatherer cultures, the human being is often regarded as on a roughly equal footing 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 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.
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. After the spirit transmigrates to another body, they take the form of a predatory animal and exact revenge.
Mysticism views humans as susceptible to an ineffable experience or realization of unity with the Absolute (see enlightenment, immanence). In monotheistic mysticism, the mystical experience focuses upon unity with God. Essentially mystic movements include Vedanta, Yoga, Zen and other schools of Buddhism, the Eleusian cults, Neoplatonism, Christian mystic orders, Jewish Kabbalah and Hasidism, Islamic Sufism, and the contemporary New Age. Mystical spiritual practices and experiences possibly, but not necessarily, coupled with theism or religious institutions have been present in all societies.
In polytheistic 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.
Polytheism is 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, and is present from the beginning of history, possibly reflected in Stone Age artwork. sacrificial rites evolved into institutionalized 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).
Monotheism generally believes that a single deity, who is either the only one in existence, or who incorporates or excels all lesser deities, created the humanity. Humans are thus 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 are alone in possessing a conscience.
In Judaism and Christianity, humanity is seen as unique among creatures in being made in the image of God, and intended for a relationship of love and obedience with God. However, it is believed, humanity's disobedience or sin broke that relationship, resulting in the Fall. Consequently, humanity is currently not living up to its intended potential for life, joy, and freedom, and instead suffers under the power of sin and death. According to the Hebrew Bible, God chose the Jews as a special people, and determined that all other people were to remain under the Noahide Laws, reflecting an emphasis on the fate of the community over the fate of the individual. Christianity introduced a greater emphasis on the individual, as well as the ideas of salvation, divine grace, and divine incarnation. Subsequently, the fusion of Hellenic and Christian thought led to the development of theology. Islam, established six centuries after Christianity, rejects the Christian belief in divine incarnation and the view of Israel as a chosen people, but retains the view of humanity as vice-regents 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.
Humanism as a philosophy defines a socio-political doctrine the bounds of which are not constrained by those of locally developed cultures, but which includes all of humanity and all issues common to human beings. Because collective spirituality often manifests as religion, the history of which is as factious as it is unitive, secular humanism grew as an answer to the need for a common philosophy that transcended the cultural boundaries of local moral codes and religions. Many humanists are religious, however, and see humanism as simply a mature expression of a common truth present in most religions. Humanists affirm the possibility of an objective truth and accept that human perception of that truth is imperfect. The most basic tenets of humanism are that humans matter and can solve human problems, and that science, freedom of speech, rational thought, democracy, and freedom in the arts are worthy pursuits or goals for all peoples. Modern humanism depends on reason and logic and rejects the supernatural.
See also: Atheism, Atman, Conscience, Ecstasy (state), Ethics, God, Humanism, Human realm, Incarnation, Karma, Korban, Morality, Mystic, Prayer, Rationalism, Reincarnation, Religion, Resurrection, Ritual, Sacrifice, Salvation, Sin, Soul, Spirituality, Worship
Although many species are social, forming groups based on genetic ties, affection, self-defense, 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 and knowledge. Group identity and acceptance can exert a powerful influence on individual behaviour, yet humans are also able to form and adapt to new groups. An individual may develop strong feelings of loyalty towards such groups.
The human individual often develops a particularly strong attachment to a small group, typically including his closest biological relatives: his 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, nations) or common geographical location and material interests (states), which are often further divided into social classes and hierarchical structures. A tribe may consist of a few hundred individuals, while the largest modern state, China, contains over a billion. Violent conflicts between states are called wars. Loyalty to a larger group of this type is called nationalism or patriotism. In extreme cases, feelings of loyalty towards an institution or authority can become pathological, leading to mass hysteria or fascism. (See also Milgram experiment, Stanford prison experiment.)
Main articles: Consciousness, Human self-reflection, Mind, Mind-body problem, Dualism, Artificial intelligence, Rationalism, Empiricism, Immanuel Kant, David Hume, Philosophy of mind, Epistemology, Materialism, Physicalism, Reductionism, Idealism.
The way the world is experienced by an individual is the subject of much debate and research in philosophy, psychology, biology, neurology, and cognitive science. Human and non-human animals are said to possess consciousness, self-awareness, or a mind, which gives rise to an individual's perception of his own existence, the passage of time, and his free will, though some philosophers argue that free will is an illusion. (See also predestination, fatalism, determinism, social determinism and biological determinism).
There is debate about the extent to which the mind constructs, rather than simply experiences, the outer world, and whether the concept of mind even makes sense. Cognitive scientist Daniel Dennett, for example, argues that there is no such thing as a narrative center called mind, but that instead there is simply a collection of sensory inputs and outputs: different kinds of software running in parallel, (Dennett, 1991). The idea that humans have a mind that is in some sense separate from their bodies, and that may be immaterial, is known as dualism, and was given its most powerful expression by the French philosopher Ren Descartes (1596-1650), who argued that, even if it seemed that everything could be doubted and that all his beliefs were false, the one thing that could not be doubted was that, in doubting, he was thinking, (Descartes, 1641). This argument is called the Cogito, short for Cogito ergo sum or "I think, therefore I am." Saint Augustine (354–430 CE) had argued in favor of the same position almost 1,300 years earlier:
You, who wish to know, do you know you are? I know it. Whence are you? I know not. Do you feel yourself single or multiple? I know not. Do you feel yourself moved? I know not. Do you know that you think? I do. (Soliloquia, 386-7 CE)
The main objection to dualism is the problem of how the mind and body interact, particularly if the mind is thought to be immaterial.
One branch of psychology, psychoanalysis, which is not regarded as a science, was devised by Sigmund Freud, and attempts to reveal, through frequent individual psychotherapy sessions, usually with a trained psychiatrist, portions of what it calls the unconscious mind. Freud divided the mind into the id (an individual's basic needs and instincts), the superego (personal and cultural values and norms), and the ego (the central, organizing self, whose job it is to satisfy the id but not upset the superego).  (See also Ego, Superego and Id.)
The Swiss psychiatrist Carl Gustav Jung, initially one of Freud's followers, founded the school of analytical psychology and introduced the notion of the collective unconscious, a term taken from philosophy and used by Jung to describe symbols or archetypes that he believed might be common to all cultures.
Thales of Miletus, when asked what was difficult, answered in a well-known apophthegm: "To Know Thyself" γνωθ σαυτον (also attributed to Socrates, and inscribed on the Temple of Apollo at Delphi). Humanity has always taken a great interest in itself. The human faculty of introspection, the urge of an individual to discover more about his essence, invariably leads to an 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 Hebrew Bible's 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 Ancient Greek philosopher Protagoras 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 use, 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 includes 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.
Human extinction refers to the possibility that the human species may become extinct, either through its own actions (for example because of pollution, or the use of nuclear weapons) or because of a natural disaster.