Mensch
Das Allgemeinste, was sich über den Menschen sagen lässt, ist dies: er lebt seit einiger Zeit (< 1 Million Jahre) auf einem schon etwas älteren (< 4,7 Milliarden Jahre) Planeten in einer mit ca. 100 Milliarden bis 500 Milliarden Exemplaren recht sternenreichen Galaxie namens Milchstraße (die ihrerseits aber auch nur eine von ein- oder zweihundert Milliarden Galaxien in unserem Universum ist). An astrophysikalischen Dimensionen gemessen ist der Mensch sehr jung: während das Universum knapp 14 Milliarden Jahre alt sein dürfte, gibt es den Menschen erst seit deutlich weniger als einer Million Jahre. Aber auch im Vergleich zu anderen Lebewesen erscheint der Mensch als Nachzügler der Evolution. Erste auf Leben hindeutende Zellstrukturen gab es schon vor 3,6 Milliarden Jahren, erste Fische und Landpflanzen vor rund einer halben Milliarde, und vor 400, bzw. 300 Millionen Jahren erste Insekten und Reptilien. Nach der bis heute größten Umweltkatastrophe der Erdgeschichte vor 251 Millionen Jahren, die rund 90% aller Meeresorganismen und 70% aller auf dem Land lebenden Wirbeltiere vernichtete, entstanden Säugetiere, Vögel und Blumen sowie natürlich die Herren der zu Ende gehenden Kreidezeit, die Dinosaurier. Erst mit deren Untergang (im Verlaufe der zweitgrößten erdgeschichtlichen Katastrophe vor 65 Millionen Jahren) tauchten vor 60 Millionen Jahren überhaupt die ersten noch sehr mäuse-, bzw. lemurenhaften Primaten, dann (vor 20 Millionen Jahren) die Hominiden und (vor 2,5 Millionen Jahren) die ersten direkten Vorläufer des Menschen auf - bis aus ihnen vor rund 200 000 Jahren der zunächst anatomisch und dann (vor 50 000 Jahren) auch in seinem Verhalten "moderne" Mensch entstand. Mit diesem "modernen" Menschen haben wir es zu tun, wenn wir von Störungen der sozialen Ordnung und des sozialen Friedens, von Sicherheit und Unsicherheit, von Aggression und Gewalt, von Tötungen, Vergewaltigungen, Diebstählen, Genoziden - kurz: von abweichendem und konformem Verhalten und von Kriminalität und Strafe sprechen.
Geschichte
The spread of humans and their large and increasing population has had a destructive impact on large areas of the environment and millions of native species worldwide. Advantages that explain this evolutionary success include a relatively larger brain with a particularly well-developed neocortex, prefrontal cortex and temporal lobes, which enable high levels of abstract reasoning, language, problem solving, sociality, and culture through social learning. Humans use tools to a much higher degree than any other animal, are the only extant species known to build fires and cook their food, as well as the only extant species to clothe themselves and create and use numerous other technologies and arts.
Humans are uniquely adept at utilizing systems of symbolic communication such as language and art for self-expression, the exchange of ideas, and organization. Humans create complex social structures composed of many cooperating and competing groups, from families and kinship networks to states. Social interactions between humans have established an extremely wide variety of values,[9] social norms, and rituals, which together form the basis of human society. The human desire to understand and influence their environment, and explain and manipulate phenomena, has been the foundation for the development of science, philosophy, mythology, and religion. The scientific study of humans is the discipline of anthropology.
Humans began to practice sedentary agriculture about 12,000 years ago, domesticating plants and animals which allowed for the growth of civilization. Humans subsequently established various forms of government, religion, and culture around the world, unifying people within a region and leading to the development of states and empires. The rapid advancement of scientific and medical understanding in the 19th and 20th centuries led to the development of fuel-driven technologies and improved health, causing the human population to rise exponentially. By 2012 the global human population was estimated to be around 7 billion.[10][11]
Contents [hide] 1 Etymology and definition 2 History 2.1 Evolution and range 2.1.1 Evidence from molecular biology 2.1.2 Evidence from the fossil record 2.1.3 Anatomical adaptations 2.2 Rise of Homo sapiens 2.3 Transition to civilization 3 Habitat and population 4 Biology 4.1 Anatomy and physiology 4.2 Genetics 4.3 Life cycle 4.4 Diet 4.5 Biological variation 4.5.1 Structure of variation 5 Psychology 5.1 Sleep and dreaming 5.2 Consciousness and thought 5.3 Motivation and emotion 5.4 Sexuality and love 6 Culture 6.1 Language 6.2 Gender roles 6.3 Kinship 6.4 Ethnicity 6.5 Society, government, and politics 6.6 Trade and economics 6.7 War 6.8 Material culture and technology 6.8.1 Body culture 6.9 Religion and spirituality 6.10 Philosophy and self-reflection 6.11 Science and mathematics 6.12 Art, music, and literature 7 See also 8 References 9 Further reading 10 External links Etymology and definition Further information: Man (word) and List of alternative names for the human species In common usage, the word "human" generally refers to the only extant species of the genus Homo — anatomically and behaviorally modern Homo sapiens. Its usage often designates differences between the species as a whole and any other nature or entity.
In scientific terms, the definition of "human" has changed with the discovery and study of the fossil ancestors of modern humans. The previously clear boundary between human and ape blurred, resulting in "Homo" referring to "human" now encompassing multiple species. There is also a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species, which are classified as a subspecies of Homo sapiens, e.g. Homo sapiens neanderthalensis.
The English adjective human is a Middle English loanword from Old French humain, ultimately from Latin hūmānus, the adjective form of homō "man". The word's use as a noun (with a plural: humans) dates to the 16th century.[12] The native English term man can refer to the species generally (a synonym for humanity), and could formerly refer to specific individuals of either sex. The latter use is now obsolete.[13] Generic uses of the term "man" are declining, in favor of reserving it for referring specifically to adult males. The word is from Proto-Germanic mannaz, from a Proto-Indo-European (PIE) root man-.
The species binomial Homo sapiens was coined by Carl Linnaeus in his 18th century work Systema Naturae, and he himself is the lectotype specimen.[14] The generic name Homo is a learned 18th century derivation from Latin homō "man", ultimately "earthly being" (Old Latin hemō, a cognate to Old English guma "man", from PIE dʰǵʰemon-, meaning "earth" or "ground").[15] The species-name sapiens means "wise" or "sapient". Note that the Latin word homo refers to humans of either gender, and that sapiens is the singular form (while there is no word sapien).
History Evolution and range Main article: Human evolution Further information: Anthropology, Homo (genus) and Timeline of human evolution The genus Homo diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids (great ape) branch of the primates. Modern humans, defined as the species Homo sapiens or specifically to the single extant subspecies Homo sapiens sapiens, proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000–60,000 years ago,[16][17] Australia around 40,000 years ago, the Americas around 15,000 years ago, and remote islands such as Hawaii, Easter Island, Madagascar, and New Zealand between the years 300 and 1280.[18][19]
Evidence from molecular biology Family tree showing the extant hominoids: humans (genus Homo), chimpanzees and bonobos (genus Pan), gorillas (genus Gorilla), orangutans (genus Pongo), and gibbons (four genera of the family Hylobatidae: Hylobates, Hoolock, Nomascus, and Symphalangus). All except gibbons are hominids.
The closest living relatives of humans are chimpanzees (genus Pan) and gorillas (genus Gorilla).[20] With the sequencing of both the human and chimpanzee genome, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%.[20][21][22] By using the technique called a molecular clock which estimates the time required for the number of divergent mutations to accumulate between two lineages, the approximate date for the split between lineages can be calculated. The gibbons (Hylobatidae) and orangutans (genus Pongo) were the first groups to split from the line leading to the humans, then gorillas (genus Gorilla) followed by the chimpanzees and bonobos (genus Pan). The splitting date between human and chimpanzee lineages is placed around 4–8 million years ago during the late Miocene epoch.[23][24][25]
Evidence from the fossil record
Skulls of 1. Gorilla 2. Australopithecus 3. Homo erectus 4. Neanderthal (La Chapelle aux Saints) 5. Steinheim Skull (Archaic Homo sapiens) 6. Caucasoid (H. Sapiens)
There is little fossil evidence for the divergence of the gorilla, chimpanzee and hominin lineages.[26][27] The earliest fossils that have been proposed as members of the hominin lineage are Sahelanthropus tchadensis dating from 7 million years ago, and Orrorin tugenensis dating from 5.7 million years ago and Ardipithecus kadabba dating to 5.6 million years ago. Each of these has been argued to be a bipedal ancestor of later hominins, but in each case the claims have been contested. It is also possible that either of these species is an ancestor of another branch of African apes, or that they represent a shared ancestor between hominins and other Hominoidea. The question of the relation between these early fossil species and the hominin lineage is still to be resolved. From these early species the australopithecines arose around 4 million years ago diverged into robust (also called Paranthropus) and gracile branches, one of which (possibly A. garhi) went on to become ancestors of the genus Homo.
The earliest members of the genus Homo are Homo habilis which evolved around 2.3 million years ago. Homo habilis is the first species for which we have positive evidence of use of stone tools. The brains of these early hominins were about the same size as that of a chimpanzee, and their main adaptation was bipedalism as an adaptation to terrestrial living. During the next million years a process of encephalization began, and with the arrival of Homo erectus in the fossil record, cranial capacity had doubled. Homo erectus were the first of the hominina to leave Africa, and these species spread through Africa, Asia, and Europe between 1.3 to 1.8 million years ago. One population of H. erectus, also sometimes classified as a separate species Homo ergaster, stayed in Africa and evolved into Homo sapiens. It is believed that these species were the first to use fire and complex tools. The earliest transitional fossils between H. ergaster/erectus and archaic humans are from Africa such as Homo rhodesiensis, but seemingly transitional forms are also found at Dmanisi, Georgia. These descendants of African H. erectus spread through Eurasia from ca. 500,000 years ago evolving into H. antecessor, H. heidelbergensis and H. neanderthalensis. The earliest fossils of anatomically modern humans are from the Middle Paleolithic, about 200,000 years ago such as the Omo remains of Ethiopia and the fossils of Herto sometimes classified as Homo sapiens idaltu.[28] Later fossils of archaic Homo sapiens from Skhul in Israel and Southern Europe begin around 90,000 years ago.[29]
Anatomical adaptations
Reconstruction of Homo habilis, the first human ancestor to use stone tools
Human evolution is characterized by a number of morphological, developmental, physiological, and behavioral changes that have taken place since the split between the last common ancestor of humans and chimpanzees. The most significant of these adaptations are 1. bipedalism, 2. increased brain size, 3. lengthened ontogeny (gestation and infancy), 4. decreased sexual dimorphism. The relationship between all these changes is the subject of ongoing debate.[30] Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus.[31]
Bipedalism is the basic adaption of the hominin line, and it is considered the main cause behind a suite of skeletal changes shared by all bipedal hominins. The earliest bipedal hominin is considered to be either Sahelanthropus[32] or Orrorin, with Ardipithecus, a full bipedal, coming somewhat later. The knuckle walkers, the gorilla and chimpanzee, diverged around the same time, and either Sahelanthropus or Orrorin may be humans' last shared ancestor with those animals. The early bipedals eventually evolved into the australopithecines and later the genus Homo. There are several theories of the adaptational value of bipedalism. It is possible that bipedalism was favored because it freed up the hands for reaching and carrying food, because it saved energy during locomotion, because it enabled long distance running and hunting, or as a strategy for avoiding hyperthermia by reducing the surface exposed to direct sun.
The human species developed a much larger brain than that of other primates – typically 1,330 cc in modern humans, over twice the size of that of a chimpanzee or gorilla.[33] The pattern of encephalization started with Homo habilis which at approximately 600 cc had a brain slightly larger than chimpanzees, and continued with Homo erectus (800–1100 cc), and reached a maximum in Neanderthals with an average size of 1200-1900cc, larger even than Homo sapiens. The pattern of human postnatal brain growth differs from that of other apes (heterochrony), and allows for extended periods of social learning and language acquisition in juvenile humans. However, the differences between the structure of human brains and those of other apes may be even more significant than differences in size.[34][35][36][37] The increase in volume over time has affected different areas within the brain unequally – the temporal lobes, which contain centers for language processing have increased disproportionately, as has the prefrontal cortex which has been related to complex decision making and moderating social behavior.[33] Encephalization has been tied to an increasing emphasis on meat in the diet,[38][39] or with the development of cooking,[40] and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex.
The reduced degree of sexual dimorphism is primarily visible in the reduction of the male canine tooth relative to other ape species (except gibbons). Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans are the only ape in which the female is fertile year round, and in which no special signals of fertility are produced by the body (such as genital swelling during estrus). Nonetheless humans retain a degree of sexual dimorphism in the distribution of body hair and subcutaneous fat, and in the overall size, males being around 25% larger than females. These changes taken together have been interpreted as a result of an increased emphasis on pair bonding as a possible solution to the requirement for increased parental investment due to the prolonged infancy of offspring.
Rise of Homo sapiens Further information: Recent African origin of modern humans, Multiregional origin of modern humans, Anatomically modern humans, Archaic human admixture with modern humans and Early human migrations
Map of early human migrations according to mitochondrial population genetics (numbers are millennia before present).
By the beginning of the Upper Paleolithic period (50,000 BP), full behavioral modernity, including language, music and other cultural universals had developed.[41][42] As modern humans spread out from Africa they encountered other hominids such as Homo neanderthalensis and the so-called Denisovans. The nature of interaction between early humans and these sister species has been a long standing source of controversy, the question being whether humans replaced these earlier species or whether they were in fact similar enough to interbreed, in which case these earlier populations may have contributed genetic material to modern humans.[43] Recent studies of the human and Neanderthal genomes suggest gene flow between archaic Homo sapiens and Neanderthals and Denisovans.[44][45][46]
This dispersal out of Africa is estimated to have begun about 70,000 years BP from northeast Africa. Current evidence suggests that there was only one such dispersal and that it only involved a few hundred individuals. The vast majority of humans stayed in Africa and adapted to a diverse array of environments.[47] Modern humans subsequently spread globally, replacing earlier hominins (either through competition or hybridization). They inhabited Eurasia and Oceania by 40,000 years BP, and the Americas at least 14,500 years BP.[48][49]
Transition to civilization Main articles: Neolithic Revolution and Cradle of civilization Further information: History of the world
The rise of agriculture, and domestication of animals, led to stable human settlements.
Until c. 10,000 years ago, humans lived as hunter-gatherers. They generally lived in small nomadic groups known as band societies. The advent of agriculture prompted the Neolithic Revolution, when access to food surplus led to the formation of permanent human settlements, the domestication of animals and the use of metal tools for the first time in history. Agriculture encouraged trade and cooperation, and led to complex society. Because of the significance of this date for human society, it is the epoch of the Holocene calendar or Human Era.
About 6,000 years ago, the first proto-states developed in Mesopotamia, Egypt's Nile Valley and the Indus Valley. Military forces were formed for protection, and government bureaucracies for administration. States cooperated and competed for resources, in some cases waging wars. Around 2,000–3,000 years ago, some states, such as Persia, India, China, Rome, and Greece, developed through conquest into the first expansive empires. Ancient Greece was the seminal civilization that laid the foundations of Western culture, being the birthplace of Western philosophy, democracy, major scientific and mathematical advances, the Olympic Games, Western literature and historiography, as well as Western drama, including both tragedy and comedy.[50] Influential religions, such as Judaism, originating in West Asia, and Hinduism, originating in South Asia, also rose to prominence at this time.
The late Middle Ages saw the rise of revolutionary ideas and technologies. In China, an advanced and urbanized society promoted innovations and sciences, such as printing and seed drilling. In India, major advancements were made in mathematics, philosophy, religion and metallurgy. The Islamic Golden Age saw major advancements in mathematics, astronomy, optics, biology, medicine, art and architecture in Muslim empires. In Europe, the rediscovery of classical learning and inventions such as the printing press led to the Renaissance in the 14th and 15th centuries. Over the next 500 years, exploration and colonialism brought great parts of the world under European control, leading to later struggles for independence. The Scientific Revolution in the 17th century and the Industrial Revolution in the 18th–19th centuries promoted major innovations in transport, such as the railway and automobile; energy development, such as coal and electricity; and government, such as representative democracy and Communism.
With the advent of the Information Age at the end of the 20th century, modern humans live in a world that has become increasingly globalized and interconnected. As of 2010, almost 2 billion humans are able to communicate with each other via the Internet,[51] and 3.3 billion by mobile phone subscriptions.[52]
Although interconnection between humans has encouraged the growth of science, art, discussion, and technology, it has also led to culture clashes and the development and use of weapons of mass destruction. Human civilization has led to environmental destruction and pollution significantly contributing to the ongoing mass extinction of other forms of life called the Holocene extinction event,[53] which may be further accelerated by global warming in the future.[54]
Habitat and population Further information: Human migration, Demography and World population
The Earth, as seen from space in October 2000, showing the extent of human occupation of the planet. The bright lights signify both the most densely inhabited areas and ones financially capable of illuminating those areas.
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 seven 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%).[citation needed]
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.[55] Between 1969 and 1972, two humans at a time spent brief intervals on the Moon. As of May 2014, 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.[56] However, other celestial bodies have been visited by human-made objects.
Since 1800, the human population has increased from one billion[57] to over seven billion,[58] In 2004, some 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas. In February 2008, the U.N. estimated that half the world's population would live in urban areas by the end of the year.[59] Problems for humans living in cities include various forms of pollution and crime,[60] especially in inner city and suburban slums. Both overall population numbers and the proportion residing in cities are expected to increase significantly in the coming decades.[61]
Humans have had a dramatic effect on the environment. Humans are apex predators, being rarely preyed upon by other species.[62] Currently, through land development, combustion of fossil fuels, and pollution, humans are thought to be the main contributor to global climate change.[63] If this continues at its current rate it is predicted that climate change will wipe out half of all plant and animal species over the next century.[64][65]
See also: City, Town, Nomad, Camping, Farm, House, Watercraft, Infrastructure, Architecture, Building and Engineering Biology
Basic anatomical features of female and male humans. These models have had body hair and male facial hair removed and head hair trimmed. The female model is wearing red nail polish on her toenails and a ring.
Vitruvian Man, Leonardo da Vinci's image is often used as an implied symbol of the essential symmetry of the human body, and by extension, of the universe as a whole.
Anatomy and physiology
Main article: Human body
Further information: Human physical appearance, Anatomically modern humans and Sex differences in humans
Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology. The human body consists of the legs, the torso, the arms, the neck, and the head. An adult human body consists of about 100 trillion (1014) cells. The most commonly defined body systems in humans are the nervous, the cardiovascular, the circulatory, the digestive, the endocrine, the immune, the integumentary, the lympathic, the muscoskeletal, the reproductive, the respiratory, and the urinary system.[66][67]
Humans, like most of the apes, lack external tail, have several blood type systems, have opposable thumbs, and are sexually dimorphic. The comparatively minor anatomical differences between humans and chimpanzees are a result of human bipedalism. As a result, humans are slower over short distances, but are among the best long-distance runners in the animal kingdom.[68][69] Humans' thinner body hair and more productive sweat glands help avoid heat exhaustion while running for long distances.[70]
As a consequence of bipedalism, human females have narrower birth canals. The construction of the human pelvis differs from other primates, as do the toes. A trade-off for these advantages of the modern human pelvis is that childbirth is more difficult and dangerous than in most mammals, especially given the larger head size of human babies compared to other primates. This means that human babies must turn around as they pass through the birth canal, which other primates do not do, and it makes humans the only species where females require help from their conspecifics[clarification needed] to reduce the risks of birthing. As a partial evolutionary solution, human fetuses are born less developed and more vulnerable. Chimpanzee babies are cognitively more developed than human babies until the age of six months, when the rapid development of human brains surpasses chimpanzees. Another difference between women and chimpanzee females is that women go through the menopause and become unfertile decades before the end of their lives. All species of non-human apes are capable of giving birth until death. Menopause probably developed as it has provided an evolutionary advantage (more caring time) to young relatives.[69]
Apart from bipedalism, humans differ from chimpanzees mostly in smelling, hearing, digesting proteins, brain size, and the ability of language. Humans brains are about three times bigger than in chimpanzees. More importantly, the brain to body ratio is much higher in humans than in chimpanzees, and humans have a significantly more developed cerebral cortex, with a larger number of neurons. The mental abilities of humans are remarkable compared to apes. Humans' ability of speech is unique among primates. Humans are able to create new and complex ideas, and to develop technology, which is unprecedented among other organisms on Earth.[69]
The average adult human male is about 1.7–1.8 metres (5.6–5.9 ft), the average adult human female is about 1.6–1.7 metres (5.2–5.6 ft) in height.[71] Shrinkage of stature may begin in middle age in some individuals, but tends to be universal[clarification needed] in the extremely aged.[72] Through history human populations have universally become taller, probably as a consequence of better nutrition, healthcare, and living conditions.[73] 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.[74] Like many other conditions, body weight and body type is influenced by both genetic susceptibility and environment and varies greatly among individuals. (see obesity)[75][76]
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.[77] Humans have about 2 million sweat glands spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on the palm of the hand and on the soles of the feet.[78]
The dental formula of humans is: 2.1.2.3 2.1.2.3 . 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 individuals. Humans are gradually losing their wisdom teeth, with some individuals having them congenitally absent.[79]
Genetics Main article: Human genetics
A graphical representation of the ideal human karyotype, including both the male and female variant of the sex chromosome (number 23).
Like all mammals, humans are a diploid eukaryotic species. Each somatic cell has two sets of 23 chromosomes, each set received from one parent; gametes have only one set of chromosomes, which is a mixture of the two parental sets. Among the 23 pairs of chromosomes there are 22 pairs of autosomes and one pair of sex chromosomes. Like other mammals, humans have an XY sex-determination system, so that females have the sex chromosomes XX and males have XY.
One human genome was sequenced in full in 2003, and currently efforts are being made to achieve a sample of the genetic diversity of the species (see International HapMap Project). By present estimates, humans have approximately 22,000 genes.[80] The variation in human DNA is very small compared to other species, possibly suggesting a population bottleneck during the Late Pleistocene (around 100,000 years ago), in which the human population was reduced to a small number of breeding pairs.[81][82] Nucleotide diversity is based on single mutations called single nucleotide polymorphisms (SNPs). The nucleotide diversity between humans is about 0.1%, i.e. 1 difference per 1,000 base pairs.[83][84] A difference of 1 in 1,000 nucleotides between two humans chosen at random amounts to about 3 million nucleotide differences, since the human genome has about 3 billion nucleotides. Most of these single nucleotide polymorphisms (SNPs) are neutral but some (about 3 to 5%) are functional and influence phenotypic differences between humans through alleles.
By comparing the parts of the genome that are not under natural selection and which therefore accumulate mutations at a fairly steady rate, it is possible to reconstruct a genetic tree incorporating the entire human species since the last shared ancestor. Each time a certain mutation (SNP) appears in an individual and is passed on to his or her descendants, a haplogroup is formed including all of the descendants of the individual who will also carry that mutation. By comparing mitochondrial DNA, which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve, must have lived around 200,000 years ago.
The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years.[85]
Life cycle See also: Childbirth and Life expectancy
A 10 mm human embryo at 5 weeks
Boy and girl before puberty
Adult man and woman in the reproductive age
Elderly man and woman
As with other mammals, human reproduction takes place as internal fertilization by sexual intercourse. During this process, the erect penis of the male is inserted into the female's vagina until the male ejaculates semen, which contains sperm. The sperm travels through the vagina and cervix into the uterus or Fallopian tubes for fertilization of the ovum. Upon fertilization and implantation, gestation then occurs within the female's uterus.
The zygote divides inside the female's uterus to become an embryo, which over a period of 38 weeks (9 months) of gestation becomes a fetus. After this span of time, the fully grown fetus 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 fetuses while they remain in the uterus.
Compared with other species, human childbirth is dangerous. Painful labors lasting 24 hours or more are not uncommon and sometimes lead to the death of the mother, the child or both.[86] This is because of both the relatively large fetal head circumference and the mother's relatively narrow pelvis.[87][88] The chances of a successful labor 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 greater than in developed countries.[89]
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.[90][not in citation given] However, low birth weight is common in developing countries, and contributes to the high levels of infant mortality in these regions.[91] 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.[92] 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.[93][94]
For various reasons, including biological/genetic causes,[95] women live on average about four years longer than men — as of 2013 the global average life expectancy at birth of a girl is estimated at 70.2 years compared to 66.1 for a boy.[96] There are significant geographical variations in human life expectancy, mostly correlated with economic development — for example life expectancy at birth in Hong Kong is 84.8 years for girls and 78.9 for boys, while in Swaziland, primarily because of AIDS, it is 31.3 years for both sexes.[97] 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. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older.[98] 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.[99] At least one person, Jeanne Calment, is known to have reached the age of 122 years;[100] higher ages have been claimed but they are not well substantiated.
Diet Main article: Human nutrition
Humans preparing a meal in Bali, Indonesia
Venus of Willensdorf statuette from the Upper Palaeolithic period
Two starved boys during the Russian famine of 1921 Humans are omnivorous, capable of consuming a wide variety of plant and animal material.[101][102] 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.[103] 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 mollusks) with wild game, which must be hunted and killed in order to be consumed.[104] It has been proposed that humans have used fire to prepare and cook food since the time of Homo erectus.[105] Around ten thousand years ago, humans developed agriculture,[106] 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.[107][108] 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. About 36 million humans die every year from causes directly or indirectly related to hunger.[109] Childhood malnutrition is also common and contributes to the global burden of disease.[110] 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,[111] while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic".[112] 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.[111]
Biological variation Main article: Human genetic variation
People in warm climates are often relatively slender, tall and dark skinned, such as these Maasai men from Kenya.
People in cold climates tend to be relatively short, heavily built and fair skinned such as these Inuit women from Canada.
No two humans – not even monozygotic twins – are genetically identical. Genes and environment influence human biological variation from visible characteristics to physiology to disease susceptibly to mental abilities. The exact influence of genes and environment on certain traits is not well understood.[113][114]
Most current genetic and archaeological evidence supports a recent single origin of modern humans in East Africa,[115] with first migrations placed at 60,000 years ago. Compared to the great apes, human gene sequences – even among African populations – are remarkably homogeneous.[116] On average, genetic similarity between any two humans is 99.9%.[117][118] There is about 2–3 times more genetic diversity within the wild chimpanzee population on a single hillside in Gombe, than in the entire human gene pool.[119][120][121][122]
The human body's ability to adapt to different environmental stresses is remarkable, allowing humans to acclimatize to a wide variety of temperatures, humidity, and altitudes. As a result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforests, arid desert, extremely cold arctic regions, and heavily polluted cities. Most other species are confined to a few geographical areas by their limited adaptability.[123]
There is biological variation in the human species — with traits such as blood type, cranial features, eye color, hair color and type, height and build, and skin color varying across the globe. Human body types vary substantially. The typical height of an adult human is between 1.4 m (4 ft 7 in) to 1.9 m (6 ft 3 in), although this varies significantly depending, among other things, on sex and ethnic origin.[124][125] Body size is partly determined by genes and is also significantly influenced by environmental factors such as diet, exercise, and sleep patterns, especially as an influence in childhood. Adult height for each sex in a particular ethnic group approximately follows a normal distribution. Those aspects of genetic variation that give clues to human evolutionary history, or are relevant to medical research, have received particular attention. For example the genes that allow adult humans to digest lactose are present in high frequencies in populations that have long histories of cattle domestication, suggesting natural selection having favored that gene in populations that depend on cow milk. Some hereditary diseases such as sickle cell anemia are frequent in populations where malaria has been endemic throughout history — it is believed that the same gene gives increased resistance to malaria among those who are unaffected carriers of the gene. Similarly, populations that have for a long time inhabited specific climates, such as arctic or tropical regions or high altitudes, tend to have developed specific phenotypes that are beneficial for conserving energy in those environments — short stature and stocky build in cold regions, tall and lanky in hot regions, and with high lung capacities at high altitudes. Similarly, skin color varies clinally with darker skin around the equator — where the added protection from the sun's ultraviolet radiation is thought to give an evolutionary advantage — and lighter skin tones closer to the poles.[126][127][128][129]
The hue of human skin and hair is determined by the presence of pigments called melanins. Human skin color can range from darkest brown to lightest peach, or even nearly white or colorless in cases of albinism.[122] Human hair ranges in color from white to red to blond to brown to black, which is most frequent.[130] Hair color 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 is an adaptation that evolved as protection against ultraviolet solar radiation, which also helps balancing folate, which is destroyed by ultraviolet radiation. Light skin pigmentation protects against depletion of vitamin D, which requires sunlight to make.[131] Skin pigmentation of contemporary humans is clinally distributed across the planet, and in general correlates with the level of ultraviolet radiation in a particular geographic area. Human skin also has a capacity to darken (tan) in response to exposure to ultraviolet radiation.[132][133][134]
Structure of variation
A Libyan, a Nubian, a Syrian, and an Egyptian, drawing by an unknown artist after a mural of the tomb of Seti I.
The ancestors of Native Americans, such as this Yanomami woman, crossed into the Americas from Northeast Asia, and genetic and linguistic evidence links them to North Asian populations, particularly those of East Siberia.[135]
Within the human species, the greatest degree of genetic variation exists between males and females. While the nucleotide genetic variation of individuals of the same sex across global populations is no greater than 0.1%, the genetic difference between males and females is between 1% and 2%. Although different in nature{[clarifyme}}, this approaches the genetic differentiation between men and male chimpanzees or women and female chimpanzees. The genetic difference between sexes contributes to anatomical, hormonal, neural, and physiological differences between men and women, although the exact degree and nature of social and environmental influences on sexes are not completely understood. Males on average are 15% heavier and 15 cm taller than females. There is a difference between body types, body organs and systems, hormonal levels, sensory systems, and muscle mass between sexes. On
Zukunft
Wie es in dieser Hinsicht langfristig weitergeht, steht buchstäblich in den Sternen. Spätestens in 500 Millionen Jahren wird es für die Pflanzen zu heiß und damit auch für Tiere zunehmend schwerer. Und selbst die einfachsten und widerstandsfähigsten Organismen (Mikroben) werden nicht mehr widerstehen können, wenn die Erde in 2,8 Milliarden Jahren die kritische Marke von 140° C erreicht: das ist für jede DNA zuviel. Leben wird es also, wenn die Erde in 5 Milliarden Jahren verglühen wird, in diesem Sonnensystem schon lange nicht mehr gegeben haben. Optimisten können daraus folgern: die Menschheit steht erst am Anfang ihrer Entwicklung. Mit ihren Vorläufern kommt sie auf eine Geschichte von 2,5 Millionen Jahren. Richtig losgelegt hat sie erst vor 200 000 Jahren. Es bleiben aber mit viel Glück nicht weniger als 500 Millionen Jahre, um bisherige Unzulänglichkeiten menschlicher Organisation zu überwinden und für die Menschheit im Laufe der nächsten Jahrmillionen ganz gemütlich eine Art Arche Noah 2.0 zu bauen, die das (Über-) Leben von der zunehmenden Unwirtlichkeit der Erde unabhängig macht. Nach Lage der Dinge wird es mit gelegentlichen Spaziergängen im All (400 km über der Erdoberfläche) oder Reisen zum Mond (385000 km) nicht getan sein, drohen dieselben Gefahren dort doch zu genau derselben Zeit. Auch Kolonien auf dem Mars (45 bis 400 Millionen km) wären keine Lösung. Erforderlich wären schon Orte außerhalb des Sonnensystems - entweder an einem sicheren Platz innerhalb unserer eigenen Galaxie (Sterne und Planeten gibt es ja genug) oder sonst eben in einer Nachbargalaxie (z.B. Alpha Centauri.
