User:Goethean/Homo sapiens

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Homo Sapiens (Latin for "wise man" or "thinking man") is the scientific name for human beings. Homo Sapiens are a mammalian species of bipedal primates belonging to the family Hominidae (the great apes).^[1] They have a highly developed brain capable of abstract reasoning, language, and introspection. This, combined with an erect body carriage that frees their upper limbs for manipulating objects, has allowed humans to make greater use of tools than any other species of animal.

Contents 1 Terminology 2 Biology 2.1 Physiology and genetics 2.2 Life cycle 2.3 Race and ethnicity 2.4 Evolution 2.5 Habitat and population 2.6 Food and drink 3 References

[edit] Terminology

Humans are commonly referred to as persons or people, and collectively as man, mankind, humankind, humanity, or the human race. Until the 20th century, human was only used adjectivally ("pertaining to mankind"). 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" (as opposed to "inhumane"; cf. humanitarian).

In general, the word people is a collective noun used to define a specific group of humans. However, when used to refer to a group of humans possessing a common ethnic, cultural or national unitary characteristic or identity, "people" is a singular noun, and as such takes an "s" in the plural; (examples: "the English-speaking peoples of the world", "the indigenous peoples of Brazil"). A distinction is also 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.

Juvenile male humans are called boys, adult males men (not to be confused with the gender-neutral man or mankind), juvenile females girls, and adult females women.

[edit] Biology

Main article: Human biology

[edit] Physiology and genetics

Main articles: Human anatomy, Human physical appearance, and Genetics of humans

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 a North American adult female is 162 centimetres (5 feet 4 inches), and the average weight is 62 kilograms (137 pounds). Human males are typically larger than females: the average height and weight of a North American adult male is 175 centimeters (5 feet 9 inches) and 78 kilograms (172 pounds).

Humans are capable of fully bipedal locomotion, thus leaving their arms available for manipulating objects using their hands, aided especially by opposable thumbs. Because human physiology has not fully adapted to bipedalism, the pelvic region and vertebral column tend to become worn, creating locomotion difficulties in old age.

Although humans appear relatively 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 on his or her body than the average chimpanzee. The main distinction is that human hairs are shorter, finer, and less colored than the average chimpanzee's, thus making them harder to see.^[2]

The color of human hair and skin is determined by the presence of pigments called melanins. Human skin color can range from very dark brown to very pale pink, while human hair ranges from blond to brown to red.^[3] Most researchers believe that skin darkening was an adaptation that evolved as a defense against ultraviolet solar radiation: melanin is an effective sun-block.^[4] The skin color 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.^[5][6]

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. Negative effects result from restriction of sleep. For instance, a sustained restriction of adult sleep to four hours per day has been shown to correlate with changes in physiology and mental state, including fatigue, aggression, and bodily discomfort. It is common in modern societies for people to get less sleep than they need, leading to a state of sleep deprivation.

Humans are a eukaryotic species. Each diploid cell has two sets of 23 chromosomes, each set received from one parent. There are 22 pairs of autosomes and one pair of sex chromosomes. By present estimates, humans have approximately 20,000–25,000 genes and share 98.4% of their DNA with their closest living evolutionary relatives, the two species of chimpanzees.^[7]

Like other mammals, humans have an XY sex determination system, so that females have the sex chromosomes XX and males have XY. The X chromosome is larger and carries many genes not on the Y chromosome, which means that recessive diseases associated with X-linked genes, such as hemophilia, affect men more often than women.

[edit] Life cycle

The human life cycle is similar to that of other placental mammals. New humans develop viviparously from conception. An egg is usually fertilized inside the female by sperm from the male through sexual intercourse, though the recent technology of in vitro fertilization is also occasionally used. The fertilized egg, called a zygote, divides inside the female's uterus to become an embryo, which over a period of thirty-eight weeks becomes a human fetus. At birth, the fully-grown fetus is expelled from the female'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 personhood to human fetuses while they remain in the uterus.

Compared with that of other species, human childbirth is fairly complicated. Painful labors lasting twenty-four hours or more are not uncommon, and may result in injury, or even death, to the child or mother, although the chances of a successful labour increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. Natural childbirth remains a common, and relatively dangerous, ordeal in remote, underdeveloped regions of the world.

Human children are born after a nine-month gestation period, and are typically 3–4 kilograms (6–9 pounds) in weight and 50–60 centimeters (20–24 inches) in height in developed countries.^[8] Helpless at birth, they continue to grow for some years, typically reaching sexual maturity at twelve to fifteen years of age. Boys continue growing for some time after this, reaching their maximum height around the age of eighteen.

The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, maturity and old age. The lengths of these stages, however—particularly the later ones—are not fixed.

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 (lowest in Uganda at 14.8 years). Life expectancy at birth is 77.2 years in the U.S. as of 2001.^[9] 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.^[10]

The number of centenarians (humans 100 years or older) in the world was estimated by the United Nations at 210,000 in 2002.^[11] The current maximum life span of humans is about 120 years (Jeanne Calment lived for 122 years and 164 days), though this limit is expected to continue to increase over time. Worldwide, there are 81 men aged 60 or over for every 100 women of the same age, and among the oldest, there are 53 men for every 100 women.

The philosophical questions of when human personhood begins and whether it persists after death are the subject of considerable debate. The prospect of death causes unease or fear for most humans. Burial ceremonies are characteristic of human societies, often inspired by beliefs in an afterlife or immortality.

[edit] Race and ethnicity

Main articles: Race and Ethnic group

Humans often categorize themselves in terms of race or ethnicity, although the scientific validity of human races as categories is disputed. Human racial categories are based on both ancestry and visible traits, especially skin color and facial features. Ethnic groups, on the other hand, are more often linked by linguistic, cultural, and national or regional ties. Self-identification with an ethnic group is based on kinship and descent. Race and ethnicity can lead to variant treatment and impact social identity, giving rise to the theory of identity politics.

Although most humans recognize that variances occur within a species, it is often a point of dispute as to what these differences entail, their importance, and whether discrimination based on race (racism) is acceptable. Some societies have placed a great deal of emphasis on race, while others have not. Three disparate historical examples include the "melting pot" of Ancient Egypt, slavery and Jim Crow laws, and the later establishment of the Civil Rights Acts, in the United States, and the racial policy of Nazi Germany.

[edit] Evolution

Main article: Human evolution

The study of human evolution encompasses the development of the genus Homo, but usually involves studying other hominids and hominines as well, such as the australopithecines. Humans are defined as hominids of the species Homo sapiens, of which the only extant subspecies is Homo sapiens sapiens; Homo sapiens idaltu (roughly translated as "elder wise man"), the other known subspecies, is extinct.^[12]

The closest living relatives of Homo sapiens are the Common Chimpanzee and the Bonobo. Full genome sequencing resulted in the conclusion that "After 6.5 [million] years of separate evolution, the differences between chimpanzee and human are just 10 times greater than those between two unrelated people and 10 times less than those between rats and mice." In fact, chimpanzee and human DNA is 96% identical.^[13] 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, a hominid skull discovered in Chad in 2001, classified as Sahelanthropus tchadensis, is approximately seven million years old, which may indicate an earlier divergence.

Two prominent scientific theories of the origins of contemporary humans exist. They concern the relationship between modern humans and other hominids. The single-origin, or "out of Africa", hypothesis proposes that modern humans evolved in Africa and later migrated outwards to replace hominids in other parts of the world. The multiregional hypothesis, on the other hand, proposes that modern humans evolved, at least in part, from independent hominid populations.^[14]

Geneticists Lynn Jorde and Henry Harpending of the University of Utah proposed that the variation in human DNA is minute compared to that of other species, and that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs—no more than 10,000—resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, the most popular being the Toba catastrophe theory.

Human evolution is characterized by a number of important physiological trends, including the expansion of the brain cavity and brain itself, which is typically 1,400 cm³ in volume, over twice that of a chimpanzee or gorilla (compare capacities). The pattern of human postnatal brain growth differs from that of other apes (heterochrony), allowing for an extended period of social learning in juvenile humans. Physical anthropologists argue that a reorganization of the structure of the brain is more important than cranial expansion itself. Other significant evolutionary changes included a reduction of the canine tooth, development of bipedal locomotion, and the descent of the larynx and hyoid bone, making speech possible. How these trends are related and what their role is in the evolution of complex social organization and culture are matters of ongoing debate in the field of physical anthropology.^[15][16]

[edit] Habitat and population

Main articles: Demography and World population

The most widely accepted view among current anthropologists is that the human species originated in the African savanna between 100 and 200 thousand years ago, colonized the rest of the Old World and Oceania by 40,000 years ago, and finally colonized the Americas by 10,000 years ago.^[17] Homo sapiens displaced groups such as Homo neanderthalensis, Homo erectus and Homo floresiensis through more successful reproduction and competition for resources.

The earliest humans were hunter-gatherers, a lifestyle well-suited to the savanna. Some later groups of humans were nomads, often to facilitate animal herding, and still later humans established permanent settlements, which was made possible by the development of agriculture. Permanent human settlements were 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 hunting populations of prey. However, humans have a great capacity for altering their habitats by various methods, such as through irrigation, urban planning, construction, transport, and manufacturing goods, and 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 all climates. Within the last few decades, humans have explored Antarctica, the ocean depths, and space, although long-term habitation of these environments is not yet possible. With a population of over six billion, humans are among of the most numerous of the large mammals. Most humans (61%) live in Asia. The vast majority of the remainder live in the Americas (14%), Africa (13%) and Europe (12%), with 5% in Oceania. (See list of countries by population and list of countries by population density.)

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 2006, 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 AD 1800 to 2000, the human population increased from one to six billion. In 2004, around 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas, and this percentage is expected to rise throughout the 21st century. Problems for humans living in cities include various forms of pollution, crime, and poverty, especially in inner city and suburban slums.

[edit] Food and drink

The need for regular intake of food and drink is prominently reflected in human culture, and has led to the development of food science. Failure to obtain food leads to hunger and eventually starvation, while failure to obtain water leads to thirst and dehydration. Both starvation and dehydration cause death if not alleviated—generally, most humans can survive for over two months without food, but at most between ten to fourteen days without water. In modern times, obesity amongst some human populations has increased to almost epidemic proportions, leading to health complications and increased mortality in some developed countries.

Humans are omnivorous animals who can consume both plant and animal products. Although early Homo sapiens employed a "hunter-gatherer" methodology as their primary means of food collection, involving combining stationary plant and fungal food sources (such as fruits, grains, tubers, and mushrooms) with wild game which must be hunted and killed in order to be consumed, many modern humans choose to be vegans or vegetarians, abstaining from eating meat for ethical or health reasons. It is believed that humans have used fire to prepare and cook food prior to eating since the time of their divergence from Homo erectus—possibly even earlier.

At least ten thousand years ago, humans developed agriculture, which has substantially altered the kind of food people eat. This has led to increased populations, the development of cities, and, due to 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.

The last century or so has produced enormous improvements in food production, preservation, storage and shipping. Today almost every locale in the world has access to not only its traditional cuisine, but many other world cuisines.

[edit] References

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• Human biology-- could be merged with homo sapiens or moved to homo sapiens sapiens.
  • Human anatomy
    • Human abdomen
    • Human back
    • Human brain
    • Human height
    • Human leg
    • Human lung
    • Human skeleton
    • Human sperm
    • Human voice
    • Human weight
  • Human development (biology)
  • Human evolution
  • Human fertilization
  • Human gait
  • Human genetics
    • Human genome
  • Human physiology
  • Human sexuality
  • Human Taxonomy
  • Human variability

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Maybe these should go somewhere else (Humanity?):

• Human behavior
• Human behavioral ecology
• Human bonding
• Human capital
• Human cognition
• Human development (biology)
• Human echolocation
• Human ecology
• Human ecosystem
• Human extinction
• Human factors
• Human geography
• Human migrations
• Human scale
• Human skin color
• Human sexual behavior
• Human survival
• Human timescales
• Sensitivity (human)