Human (Homo sapiens)


Scientific classification

Kingdom:        Animalia

Phylum:           Chordata

Class:   Mammalia

Order:  Primates

Family:            Hominidae

Genus: Homo

Species:           H. sapiens

Subspecies:      H. s. sapiens

Trinomial name

Homo sapiens sapiens

Humans, known taxonomically as Homo sapiens (Latin: "wise man" or "knowing man"), are the only living species in the Homo genus of bipedal primates in Hominidae, the great ape family. Anatomically modern-appearing humans originated in Africa about 200,000 years ago, reaching full behavioural modernity around 50,000 years ago.

Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving. This mental capability, combined with an erect body carriage that frees the hands for manipulating objects, has allowed humans to make far greater use of tools than any other living species on Earth. Other higher-level thought processes of humans, such as self-awareness, rationality, and sapience, are considered to be defining features of what constitutes a "person". Like most higher primates, humans are social animals. However, humans are uniquely adept at utilizing systems of communication for self-expression, the exchange of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families to nations. Social interactions between humans have established an extremely wide variety of values, social norms, and rituals, which together form the basis of human society. With individuals widespread in every continent except Antarctica, humans are a cosmopolitan species. As of January 2011, the population of humans was estimated to be about 6.89 billion.

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




Habitat and population

Early human settlements were dependent on proximity to water and, depending on the lifestyle, other natural resources used for subsistence, such as populations of animal prey for hunting and arable land for growing crops and grazing livestock. But humans have a great capacity for altering their habitats by means of technology; through irrigation, urban planning, construction, transport, manufacturing goods, deforestation and desertification. Deliberate habitat alteration is often done with the goals of increasing material wealth, increasing thermal comfort, improving the amount of food available, improving aesthetics, or improving ease of access to resources or other human settlements. With the advent of large-scale trade and transport infrastructure, proximity to these resources has become unnecessary, and in many places, these factors are no longer a driving force behind the growth and decline of a population. Nonetheless, the manner in which a habitat is altered is often a major determinant in population change.


Technology has allowed humans to colonize all of the continents and adapt to virtually all climates. Within the last century, humans have explored Antarctica, the ocean depths, and outer space, although large-scale colonization of these environments is not yet feasible. With a population of over six billion, humans are among the most numerous of the large mammals. Most humans (61%) live in Asia. The remainder live in the Americas (14%), Africa (14%), Europe (11%), and Oceania (0.5%).

Human habitation within closed ecological systems in hostile environments, such as Antarctica and outer space, is expensive, typically limited in duration, and restricted to scientific, military, or industrial expeditions. Life in space has been very sporadic, with no more than thirteen humans in space at any given time. Between 1969 and 1972, two humans at a time spent brief intervals on the Moon. As of January 2011, no other celestial body has been visited by humans, 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. However, other celestial bodies have been visited by human-made objects. Since 1800, the human population has increased from one billion to over six billion. In 2004, some 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas, and this percentage is expected to continue to rise throughout the 21st century. In February 2008, the U.N. estimated that half the world's population will live in urban areas by the end of the year. Problems for humans living in cities include various forms of pollution and crime, especially in inner city and suburban slums. Humans have had a dramatic effect on the environment. As humans are rarely preyed upon, they have been described as super predators. Currently, through land development, combustion of fossil fuels and pollution, humans are thought to be the main contributor to global climate change. Human activity is believed to be a major contributor to the ongoing Holocene extinction event, which is a form of mass extinction. If this continues at its current rate it is predicted that it will wipe out half of all species over the next century.


Human body types vary substantially. Although body size is largely determined by genes, it is also significantly influenced by environmental factors such as diet and exercise. The average height of an adult human is about 1.5 to 1.8 m (5 to 6 feet) tall, although this varies significantly from place to place and depending on ethnic origin. The average mass of an adult human is 54–64 kg (120–140 lbs) for females and 76–83 kg (168–183 lbs) for males. Weight can also vary greatly (e.g. obesity). Unlike most other primates, humans are capable of fully bipedal locomotion, thus leaving their arms available for manipulating objects using their hands, aided especially by opposable thumbs.

 Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area, the average human has more hair follicles on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see. The hue of human skin and hair is determined by the presence of pigments called melanin’s. Human skin hues can range from very dark brown to very pale pink. Human hair ranges from white to brown to red to most commonly black. This depends on the amount of melanin (an effective sun blocking pigment) in the skin and hair, with hair melanin concentrations in hair fading with increased age, leading to grey or even white hair. Most researchers believe that skin darkening was an adaptation that evolved as a protection against ultraviolet solar radiation. However, more recently it has been argued that particular skin colours are an adaptation to balance folate, which is destroyed by ultraviolet radiation, and vitamin D, which requires sunlight to form. The skin pigmentation of contemporary humans is geographically stratified, and in general correlates with the level of ultraviolet radiation. Human skin also has a capacity to darken (sun tanning) in response to exposure to ultraviolet radiation. Humans tend to be physically weaker than other similarly sized primates, with young, conditioned male humans having been shown to be unable to match the strength of female orangutans which are at least three times stronger. The construction of the human pelvis differs from other primates, as do the toes. As a result, humans are slower for short distances than most other animals, but are among the best long-distance runners in the animal kingdom. Humans' thinner body hair and more productive sweat glands also helps avoid heat exhaustion while running for long distances. For this reason persistence hunting was most likely a very successful strategy for early humans – in this method, prey is chased until it is literally exhausted. This may have also helped the early human Cro-Magnon population out-compete the Neanderthal population for food. The otherwise physically stronger Neanderthal would have much greater difficulty hunting in this way, and much more likely hunted larger game in close quarters. A trade-off for these advantages of the modern human pelvis is that childbirth is more difficult and dangerous. The construction of modern human shoulders enable throwing weapons, which also were much more difficult or even impossible for Neanderthal competitors to use effectively.

Constituents of the human body in a person weighing 60 kg Constituent     Weight            Percentage of atoms

Oxygen           38.8 kg            25.5 %

Carbon            10.9 kg            9.5 %

Hydrogen        6.0 kg  63.0 %

Nitrogen          1.9 kg  1.4 %

Other   2.4 kg  0.6 %

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 specimens. Humans are gradually losing their wisdom teeth, with some individuals having them congenitally absent.

Life cycle

The human life cycle is similar to that of other placental mammals. The zygote divides inside the female's uterus to become an embryo, which over a period of thirty-eight weeks (9 months) of gestation becomes a foetus. After this span of time, the fully grown foetus is birthed from the woman's body and breathes independently as an infant for the first time. At this point, most modern cultures recognize the baby as a person entitled to the full protection of the law, though some jurisdictions extend various levels of personhood earlier to human foetuses while they remain in the uterus. Compared with other species, human childbirth is dangerous. Painful labours lasting twenty-four hours or more are not uncommon and sometimes leads to the death of the mother, or the child. This is because of both the relatively large fetal head circumference (for housing the brain) and the mother's relatively narrow pelvis (a trait required for successful bipedalism, by way of natural selection).The chances of a successful labour increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times more common than in developed countries. In developed countries, infants are typically 3–4 kg (6–9 pounds) in weight and 50–60 cm (20–24 inches) in height at birth. However, low birth weight is common in developing countries, and contributes to the high levels of infant mortality in these regions. Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 12 to 15 years of age. Females continue to develop physically until around the age of 18, whereas male development continues until around age 21. The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, adulthood and old age. The lengths of these stages, however, have varied across cultures and time periods. Compared to other primates, humans experience an unusually rapid growth spurt during adolescence, where the body grows 25% in size. Chimpanzees, for example, grow only 14%, with no pronounced spurt. The presence of the growth spurt is probably necessary to keep children physically small until they are psychologically mature. Humans are one of the few species in which females undergo menopause. It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring and/or their children (the grandmother hypothesis), rather than by continuing to bear children into old age.

There are significant differences in life expectancy around the world. The developed world is generally aging, with the median age around 40 years. In the developing world the median age is between 15 and 20 years. Life expectancy at birth in Hong Kong is 84.8 years for a female and 78.9 for a male, while in Swaziland, primarily because of AIDS, it is 31.3 years for both sexes. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older. The number of centenarians (humans of age 100 years or older) in the world was estimated by the United Nations at 210,000 in 2002. At least one person, Jeanne Calment, is known to have reached the age of 122 years; higher ages have been claimed but they are not well substantiated. Worldwide, there are 81 men aged 60 or older for every 100 women of that age group, and among the oldest, there are 53 men for every 100 women.


Humans are omnivorous, capable of consuming plant, animal, and inorganic material. Varying with available food sources in regions of habitation, and also varying with cultural and religious norms, human groups have adopted a range of diets, from purely vegetarian to primarily carnivorous. In some cases, dietary restrictions in humans can lead to deficiency diseases; however, stable human groups have adapted to many dietary patterns through both genetic specialization and cultural conventions to use nutritionally balanced food sources. The human diet is prominently reflected in human culture, and has led to the development of food science. Until the development of agriculture approximately 10,000 years ago, Homo sapiens employed a hunter-gatherer method as their sole means of food collection. This involved combining stationary food sources (such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic molluscs) with wild game, which must be hunted and killed in order to be consumed. It has been proposed that members of H. sapiens have used fire to prepare and cook food since the time of their divergence from Homo rhodesiensis (which itself had previously speciated from Homo erectus). Around ten thousand years ago, humans developed agriculture, which substantially altered their diet. This change in diet may also have altered human biology; with the spread of dairy farming providing a new and rich source of food, leading to the evolution of the ability to digest lactose in some adults. Agriculture led to increased populations, the development of cities, and because of increased population density, the wider spread of infectious diseases. The types of food consumed, and the way in which they are prepared, has varied widely by time, location, and culture. In general, humans can survive for two to eight weeks without food, depending on stored body fat. Survival without water is usually limited to three or four days. Lack of food remains a serious problem, with about 36 million humans starving to death every year. Childhood malnutrition is also common and contributes to the global burden of disease. However global food distribution is not even, and obesity among some human populations has increased rapidly, leading to health complications and increased mortality in some developed, and a few developing countries. Worldwide over one billion people are obese, while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic". Obesity is caused by consuming more calories than are expended, so excessive weight gain is usually caused by a combination of an energy-dense high fat diet and insufficient exercise.

Consciousness and thought.

Humans are one of only nine species to pass the mirror test—which tests whether an animal recognizes its reflection as an image of itself—along with all the great apes (gorillas, chimpanzees, orangutans, bonobos), Bottlenose dolphins, Asian elephants, European Magpies and Orcas. Most human children will pass the mirror test at 18 months old. However, the usefulness of this test as a true test of consciousness has been disputed, and this may be a matter of degree rather than a sharp divide. Monkeys have been trained to apply abstract rules in tasks. The human brain perceives the external world through the senses, and each individual human is influenced greatly by his or her experiences, leading to subjective views of existence and the passage of time. Humans are variously said to possess consciousness, self-awareness, and a mind, which correspond roughly to the mental processes of thought. These are said to possess qualities such as self-awareness, sentience, sapience, and the ability to perceive the relationship between oneself and one's environment. The extent to which the mind constructs or experiences the outer world is a matter of debate, as are the definitions and validity of many of the terms used above. The philosopher of cognitive science Daniel Dennett, for example, argues that there is no such thing as a narrative centre called the "mind", but that instead there is simply a collection of sensory inputs and outputs: different kinds of "software" running in parallel. Psychologist B.F. Skinner argued that the mind is an explanatory fiction that diverts attention from environmental causes of behaviour, and that what are commonly seen as mental processes may be better conceived of as forms of covert verbal behaviour. Humans study the more physical aspects of the mind and brain, and by extension of the nervous system, in the field of neurology, the more behavioural in the field of psychology, and a sometimes loosely defined area between in the field of psychiatry, which treats mental illness and behavioural disorders. Psychology does not necessarily refer to the brain or nervous system, and can be framed purely in terms of phenomenological or information processing theories of the mind. Increasingly, however, an understanding of brain functions is being included in psychological theory and practice, particularly in areas such as artificial intelligence, neuropsychology, and cognitive neuroscience. The nature of thought is central to psychology and related fields. Cognitive psychology studies cognition, the mental processes' underlying behaviour. It uses information processing as a framework for understanding the mind. Perception, learning, problem solving, memory, attention, language and emotion are all well researched areas as well. Cognitive psychology is associated with a school of thought known as cognitivism, whose adherents argue for an information processing model of mental function, informed by positivism and experimental psychology. Techniques and models from cognitive psychology are widely applied and form the mainstay of psychological theories in many areas of both research and applied psychology. Largely focusing on the development of the human mind through the life span, developmental psychology seeks to understand how people come to perceive, understand, and act within the world and how these processes change as they age. This may focus on intellectual, cognitive, neural, social, or moral development. Some philosophers divide consciousness into phenomenal consciousness, which is experience itself, and access consciousness, which is the processing of the things in experience. Phenomenal consciousness is the state of being conscious, such as when they say "I am conscious." Access consciousness is being conscious of something in relation to abstract concepts, such as when one says "I am conscious of these words." Various forms of access consciousness include awareness, self-awareness, conscience, stream of consciousness, Husserl's phenomenology, and intentionality. The concept of phenomenal consciousness, in modern history, according to some, is closely related to the concept of qualia. Social psychology links sociology with psychology in their shared study of the nature and causes of human social interaction, with an emphasis on how people think towards each other and how they relate to each other. The behaviour and mental processes, both human and non-human, can be described through animal cognition, ethology, evolutionary psychology, and comparative psychology as well. Human ecology is an academic discipline that investigates how humans and human societies interact with both their natural environment and the human social environment.

Motivation and emotion

Motivation is the driving force of desire behind all deliberate actions of humans. Motivation is based on emotion, specifically, on the search for satisfaction (positive emotional experiences), and the avoidance of conflict. Positive and negative is defined by the individual brain state, which may be influenced by social norms: a person may be driven to self-injury or violence because their brain is conditioned to create a positive response to these actions. Motivation is important because it is involved in the performance of all learned responses. Within psychology, conflict avoidance and the libido are seen to be primary motivators. Within economics, motivation is often seen to be based on incentives; these may be financial, moral, or coercive. Religions generally posit divine or demonic influences. Happiness, or the state of being happy, is a human emotional condition. The definition of happiness is a common philosophical topic. Some people might define it as the best condition that a human can have—a condition of mental and physical health. Others define it as freedom from want and distress; consciousness of the good order of things; assurance of one's place in the universe or society. Emotion has a significant influence on, or can even be said to control, human behaviour, though historically many cultures and philosophers have for various reasons discouraged allowing this influence to go unchecked. Emotional experiences perceived as pleasant, such as love, admiration, or joy, contrast with those perceived as unpleasant, like hate, envy, or sorrow. There is often a distinction made between refined emotions that are socially learned and survival oriented emotions, which are thought to be innate. Human exploration of emotions as separate from other neurological phenomena is worthy of note, particularly in cultures where emotion is considered separate from physiological state. In some cultural medical theories emotion is considered so synonymous with certain forms of physical health that no difference is thought to exist. The Stoics believed excessive emotion was harmful, while some Sufi teachers felt certain extreme emotions could yield a conceptual perfection, what is often translated as ecstasy. In modern scientific thought, certain refined emotions are considered a complex neural trait innate in a variety of domesticated and non-domesticated mammals. These were commonly developed in reaction to superior survival mechanisms and intelligent interaction with each other and the environment; as such, refined emotion is not in all cases as discrete and separate from natural neural function as was once assumed. However, when humans function in civilized tandem, it has been noted that uninhibited acting on extreme emotion can lead to social disorder and crime.



Sexuality and love

Human sexuality, besides ensuring biological reproduction, has important social functions: it creates physical intimacy, bonds, and hierarchies among individuals; and in a hedonistic sense to the enjoyment of activity involving sexual gratification. Sexual desire, or libido, is experienced as a bodily urge, often accompanied by strong emotions such as love, ecstasy and jealousy. The extreme importance of sexuality in the human species can be seen in a number of physical features, among them hidden ovulation, the evolution of external scrotum and penis suggesting sperm competition, the absence of an os penis, permanent secondary sexual characteristics, the forming of pair bonds based on sexual attraction as a common social structure and sexual ability in females outside of ovulation. These adaptations indicate that the importance of sexuality in humans is on a par with that found in the Bonobo, and that the complex human sexual behaviour has a long evolutionary history. Human choices in acting on sexuality are commonly influenced by cultural norms, which vary widely. Restrictions are often determined by religious beliefs or social customs. The pioneering researcher Sigmund Freud believed that humans are born polymorphously perverse, which means that any number of objects could be a source of pleasure. According to Freud, humans then pass through five stages of psychosexual development (and can fixate on any stage because of various traumas during the process). For Alfred Kinsey, another influential sex researcher, people can fall anywhere along a continuous scale of sexual orientation (with only small minorities fully heterosexual or homosexual). Recent studies of neurology and genetics suggest people may be born predisposed to various sexual tendencies.

Race and ethnicity

Humans often categorize themselves in terms of race or ethnicity, sometimes on the basis of differences in appearance. Human racial categories have been based on both ancestry and visible traits, especially facial features, skin colour and hair texture. Most current genetic and archaeological evidence supports a recent single origin of modern humans in East Africa. Current genetic studies have demonstrated that humans on the African continent are most genetically diverse. However, compared to the other great apes, human gene sequences are remarkably homogeneous. The predominance of genetic variation occurs within racial groups, with only 5 to 15% of total variation occurring between groups. Thus the scientific concept of variation in the human genome is largely incongruent with the cultural concept of ethnicity or race.  Ethnic groups are defined by linguistic, cultural, ancestral, national or regional ties. Self-identification with an ethnic group is usually based on kinship and descent. Race and ethnicity are among major factors in social identity giving rise to various forms of identity politics, e.g., racism. (Humans have turned to violence and social exclusion as part of their identity politics; a side effect is name-calling, which has produced numerous offensive terms for humans.) There is no scientific consensus of a list of the human races, and few anthropologists endorse the notion of human "race". For example, a colour terminology for race includes the following in a classification of human races: Black (e.g. Sub-Saharan Africa), Red (e.g. Native Americans), Yellow (e.g. East Asians) and White (e.g. Europeans). Referring to natural species, in general, the term "race" is obsolete, particularly if a species is uniformly distributed on a territory. In its modern scientific connotation, the term is not applicable to a species as genetically homogeneous as the human one, as stated in the declaration on race (UNESCO 1950). Genetic studies have substantiated the absence of clear biological borders, thus the term "race" is rarely used in scientific terminology, both in biological anthropology and in human genetics.  What in the past had been defined as "races"—e.g., whites, blacks, or Asians—are now defined as "ethnic groups" or "populations", in correlation with the field (sociology, anthropology, genetics) in which they are considered


The capacity humans have to transfer concepts, ideas and notions through speech and writing is unrivalled in known species. Unlike the call systems of other primates that are closed, human language is far more open, and gains variety in different situations. The human language has the quality of displacement, using words to represent things and happenings that are not presently or locally occurring, but elsewhere or at a different time. In this way data networks are important to the continuing development of language. The faculty of speech is a defining feature of humanity, possibly predating phylogenetic separation of the modern population. Language is central to the communication between humans, as well as being central to the sense of identity that unites nations, cultures and ethnic groups. The invention of writing systems at least 5,000 years ago allowed the preservation of language on material objects, and was a major step in cultural evolution. The science of linguistics describes the structure of language and the relationship between languages. There are approximately 6,000 different languages currently in use, including sign languages, and many thousands more that are considered extinct.