Human

Homo sapiens idaltu (extinct)

Biology

Anatomy and physiology

Humans exhibit fully bipedal locomotion. This leaves the forelimbs available for manipulating objects using opposable thumbs.

Related Topics:
Bipedal locomotion - Opposable thumb

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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 (5'4") and the mean weight is 62 kg (137 lb). North American adult males are typically larger: 175 cm (5'9") and 78 kilograms (172 lb).

Related Topics:
Diet - Cm - Kg - Lb

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Human skin is relatively hairless in comparison to other primates. The colour of human hair and skin is determined by the presence of coloured pigments called melanins. Most researchers believe that skin darkening was an adaptation that evolved as a defence against UV solar radiation; melanin is an effective sunblock. The skin colour of contemporary humans can range from very dark brown to very pale pink. It is geographically stratified and in general correlates with the environmental level of UV. Human skin and hair colour is controlled in part by the MC1R gene. For example, the red hair and pale skin of some Europeans is the result of mutations in MC1R. Human skin has a capacity to darken (sun tanning) in response to UV exposure. Variation in the ability to sun tan is also controlled in part by MC1R.

Related Topics:
Melanin - UV - MC1R - Red hair - Mutation - Sun tanning

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Because humans are bipedal, the pelvic region and spinal column tend to get worn, creating locomotion difficulties in old age.

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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).

Related Topics:
Food - Drink - Food science - Hunger - Starvation - Dehydration - Thirst - Death - Famine - Malnutrition

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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.)

Related Topics:
Sleep - Modern - Sleep deprivation

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The human body is subject to an ageing process and to illness. Medicine is the science that explores methods of preserving bodily health.

Related Topics:
Ageing - Illness - Medicine - Health

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Life cycle

The human life cycle is similar to that of other placental mammals. New human life develops from conception. An egg is usually fertilised inside the female by sperm from the male through sexual intercourse, though in vitro fertilisation methods are also used. The fertilized egg is called a zygote. The zygote divides inside the female's uterus to become an embryo which over a period of 38 weeks becomes the foetus. At birth, the fully grown foetus is expelled from the female's body and breathes independently as a baby for the first time. At this point, most modern cultures recognise the baby as a person entitled to the full protection of the law, though some jurisdictions extend personhood to human foetuses while they remain in the uterus.

Related Topics:
Life cycle - Placenta - Mammal - Life - Conception - Egg - Sperm - Sexual intercourse - ''in vitro'' - Zygote - Uterus - Embryo - Foetus - Baby - Person - Law - Personhood

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Compared with that of other species, human childbirth is relatively complicated. Painful labours lasting 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 labour increased significantly during the twentieth century in wealthier countries. Natural childbirth 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.

Related Topics:
Childbirth - Injury - Natural childbirth

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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 in developed countries. http://www.childinfo.org/eddb/lbw 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.

Related Topics:
Gestation - Sexual maturity

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The human lifespan can be split into a number of stages: infancy, childhood, adolescence, young adulthood, maturity and old age, though the lengths of these stages, especially the later ones, are not fixed.

Related Topics:
Infancy - Childhood - Adolescence - Young adulthood - Maturity - Old age

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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. http://www.cdc.gov/nchs/fastats/lifexpec.htm 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. http://www.cia.gov/cia/publications/factbook

Related Topics:
Life expectancy - Monaco - Developing world - Uganda - 2001 - Singapore - Botswana - AIDS - European - African

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The number of centenarians in the world was estimated by the United Nations http://www.un.org/ageing/note5713.doc.htm 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.

Related Topics:
Centenarian - United Nations - 2002 - Life span

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The philosophical questions of when human personhood begins and whether it persists after death are the subject of considerable debate. 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).

Related Topics:
Death - Fear - Near-death experience - Burial - Afterlife - Inheritance - Ancestor worship - Immortality

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Genetics

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. At present estimate, humans have approximately 20,000–25,000 genes and share 95% of their DNA with their closest living evolutionary relatives, the two species of chimpanzees. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12368483 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 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 haemophilia more often than women.

Related Topics:
Eukaryotic - Diploid - Cell - Chromosome - Autosome - Sex chromosome - Gene - DNA - Chimpanzee - Mammal - XY sex determination system - Male - Recessive - Blood - Hemizygous - Haemophilia

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Race and ethnicity

Humans categorise themselves and others in terms of race or ethnicity when it is useful to do so. Racial categories are more likely to be primarily based on biological qualities, such as skin colour, facial features, ancestry, and other genetic variances, with cultural and historical differences also an influence. Identification of ethnic groups, however, are more likely to primarily be based on cultural affiliations. When in human society race and ethnicity lead to variant treatment of people based on perceived differences, it is thought to impact on what is presently termed social identity, hence giving rise to the recent theory of identity politics in race and ethnicity. Ideologies of race or ethnicity are related to concepts of kinship and descent.

Related Topics:
Race - Ethnicity - Social identity - Identity politics - Kinship and descent

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Although most humans recognise that variances occur within a species, it is often a point of dispute as to what these differences entail, and despite scientific findings that the human species is fairly similar in terms of brain size and functional capacity, discrimination by humans based on one's own race as opposed to another's (racism) is still very much an issue in the early twenty-first century.

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Habitat

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 colonise 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.

Related Topics:
Savanna - Human evolution - Vagina gentium - Environment of Evolutionary Adaptedness - Continents - Antarctica - Ocean - Space - Mammal

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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.)

Related Topics:
Asia - Americas - Africa - Europe - List of countries by population - List of countries by population density

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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.

Related Topics:
Hunting-gathering - Nomad - Habitats - Agriculture - Irrigation - Urban planning - Construction - Transport - Manufacturing

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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.

Related Topics:
Water - Crops - Livestock - Prey

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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 ionising 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 2005, 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.

Related Topics:
Closed ecological system - Antarctica - Outer space - Ionising radiation - Yuri Gagarin - 1961 - 1969 - 1974 - Moon - As of 2005 - Celestial body - International Space Station - October 31 - 2000

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Population

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 billion out of 6.3 billion people live in urban centres, 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.

Related Topics:
1800 - The human population - Billion - 21st century - As of 2004 - Urban - Cities - Pollution - Crime - Poverty - Suburb

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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, called the Toba catastrophe theory, being the eruption of a volcano at Lake Toba.

Related Topics:
Geneticists - University of Utah - DNA - Toba catastrophe theory - Lake Toba

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Evolution and creation

The study of human evolution encompasses many scientific disciplines, but most notably physical anthropology and genetics. The term "human", in the context of human evolution, refers to the genus Homo, but studies of human evolution usually include other hominids and hominines, such as the australopithecines.

Related Topics:
Human evolution - Physical anthropology - Genetics - Homo - Hominid - Hominine - Australopithecines

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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 respectively, given that they share a recent ancestor with man. http://news.nationalgeographic.com/news/2003/05/0520_030520_chimpanzees.html

Related Topics:
Species - Subspecies - Chimpanzee - Pan troglodytes - Pan paniscus

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Full genome sequencing resulted in these conclusions: "After 6 years of separate evolution, the differences between chimp and human are just 10 times greater than those between two unrelated people and 10 times less than those between rats and mice." Chimp and human DNA is 96% identical

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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, in 2001 a hominine skull approximately seven million years old, classified as Sahelanthropus tchadensis, was discovered in Chad and seems to indicate an earlier divergence from the ape lineage.

Related Topics:
Lineage - 2001 - Sahelanthropus tchadensis - Chad

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Two prominent scientific theories of the origins of contemporary humans exist. They concern the relationship between modern humans and other hominids:

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The single-origin or "out of africa" hypothesis proposes that modern humans evolved in Africa and later replaced hominids in other parts of the world.

Related Topics:
Single-origin - Out of africa

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The multiregional hypothesis proposes that modern humans evolved at least in part from independent hominid populations.

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Human evolution is characterised by a number of important physiological trends:

Related Topics:
Human evolution - Physiological

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• expansion of the brain cavity and brain itself, which is typically 1,400 cm³ in volume, over twice that of a chimpanzee or gorilla. 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 reorganisation of the structure of the brain is more important than cranial expansion itself;
• canine tooth reduction;
• bipedal locomotion;
• descent of the larynx, which makes speech possible.

How these trends are related and what their role is in the evolution of complex social organisation and culture are matters of ongoing debate.

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While little attention is generally given to humanities future evolution, transhumanism and eugenics involve the intentional crafting of that process. Nazi Germany made an organised attempt at selective breeding and the extremination of those they deemed inferior. The lebensborn program was one example of that.

Related Topics:
Transhumanism - Eugenics - Nazi Germany - Selective breeding - Lebensborn

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Creationism or creation theology is the belief that humans, the Earth, and the universe were created by a supreme being or deity. The event itself may be seen either as an act of creation (ex nihilo) or the emergence of order from preexisting chaos (demiurge).

Related Topics:
Creationism - Theology - Earth - Universe - Supreme being - Deity - Ex nihilo - Demiurge

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Essentially every culture has its characteristic origin beliefs. Many who hold "creation" beliefs consider such belief to be a part of religious faith, and hence compatible with, or otherwise unaffected by scientific views while others maintain the scientific data is compatible with creationism. Proponents of evolutionary creationism may claim that understood scientific mechanisms are simply aspects of supreme creation. Otherwise, science-oriented believers may consider the scriptural account of creation as simply a metaphor.

Related Topics:
Origin beliefs - Faith - Scientific - Evolutionary creationism - Scriptural - Creation - Metaphor

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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. This is closely related to religious eschatology.

Related Topics:
Human extinction - Extinct - Pollution - Nuclear weapon - Eschatology

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Intelligence

see below: Human Consciousness

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Most humans consider their species to be 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 http://www.hindustantimes.com/news/181_935198,00300006.htm, and the bottlenose dolphin very similar to humans. (Sharks have the highest for a fish; and the octopus has the highest for an invertebrate.)

Related Topics:
Brain-to-body-mass ratio - Encephalization quotient - Tree shrew - Bottlenose dolphin - Shark - Fish - Octopus - Invertebrate

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The human ability to abstract may be unparalleled in the animal kingdom. Human beings are one of five species to pass the mirror test – which tests whether an animal recognises 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.

Related Topics:
Mirror test - Chimpanzee - Bonobo - Orangutan - Dolphin

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