Life in space has been very sporadic, with no more than thirteen humans in space at any given time. Most other species are confined to a few geographical areas by their limited adaptability. Archived PDF from the original on 9 August Politics is the process by which decisions are made within groups; this process often involves conflict as well as compromise. These fields have also overlapped in the forms of marines , paratroopers , aircraft carriers , and surface-to-air missiles , among others. University of Chicago Press.
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. 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.
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.
Human skin also has a capacity to darken tan in response to exposure to ultraviolet radiation. 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. 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.
There is a difference between body types, body organs and systems, hormonal levels, sensory systems, and muscle mass between sexes. Women generally have a higher body fat percentage than men. Women have lighter skin than men of the same population; this has been explained by a higher need for vitamin D which is synthesized by sunlight in females during pregnancy and lactation.
As there are chromosomal differences between females and males, some X and Y chromosome related conditions and disorders only affect either men or women. Other conditional differences between males and females are not related to sex chromosomes. Even after allowing for body weight and volume, the male voice is usually an octave deeper than the female voice.
Women have a longer life span in almost every population around the world. They also have higher circulating clotting factors vitamin K , pro thrombin and platelets. These differences lead to faster healing of wounds and higher peripheral pain tolerance. Additionally, they produce more antibodies at a faster rate than males.
Hence they develop fewer infectious diseases and these continue for shorter periods. One proposed explanation is that human sexuality has developed more in common with its close relative the bonobo , which exhibits similar sexual dimorphism, is polygynandrous and uses recreational sex to reinforce social bonds and reduce aggression.
Humans of the same sex are There is extremely little variation between human geographical populations, and most of the variation that does occur is at the personal level within local areas, and not between populations. Two randomly chosen Koreans may be genetically as different as a Korean and an Italian. Genetic data shows that no matter how population groups are defined, two people from the same population group are about as different from each other as two people from any two different population groups.
Current genetic research has demonstrated that humans on the African continent are the most genetically diverse. The genetic structure of Africans was traced to 14 ancestral population clusters. Human genetic diversity decreases in native populations with migratory distance from Africa and this is thought to be the result of bottlenecks during human migration.
Only part of Africa's population migrated out of the continent, bringing just part of the original African genetic variety with them. African populations harbor genetic alleles that are not found in other places of the world. All the common alleles found in populations outside of Africa are found on the African continent.
Geographical distribution of human variation is complex and constantly shifts through time which reflects complicated human evolutionary history.
Most human biological variation is clinally distributed and blends gradually from one area to the next. Groups of people around the world have different frequencies of polymorphic genes. Furthermore, different traits are non-concordant and each have different clinal distribution. Adaptability varies both from person to person and from population to population. The most efficient adaptive responses are found in geographical populations where the environmental stimuli are the strongest e.
Tibetans are highly adapted to high altitudes. The clinal geographic genetic variation is further complicated by the migration and mixing between human populations which has been occurring since prehistoric times.
Human variation is highly non-concordant: Skin and hair color are not correlated to height, weight, or athletic ability. Human species do not share the same patterns of variation through geography. Skin color varies with latitude and certain people are tall or have brown hair. There is a statistical correlation between particular features in a population, but different features are not expressed or inherited together.
Thus, genes which code for superficial physical traits—such as skin color, hair color, or height—represent a minuscule and insignificant portion of the human genome and do not correlate with genetic affinity. Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other.
Despite pygmy populations of South East Asia Andamanese having similar physical features with African pygmy populations such as short stature, dark skin, and curly hair, they are not genetically closely related to these populations. Due to practices of group endogamy , allele frequencies cluster locally around kin groups and lineages, or by national, ethnic, cultural and linguistic boundaries, giving a detailed degree of correlation between genetic clusters and population groups when considering many alleles simultaneously.
Despite this, there are no genetic boundaries around local populations that biologically mark off any discrete groups of humans. Human variation is continuous, with no clear points of demarcation. There are no large clusters of relatively homogeneous people and almost every individual has genetic alleles from several ancestral groups. The human brain, the focal point of the central nervous system in humans, controls the peripheral nervous system.
In addition to controlling "lower," involuntary, or primarily autonomic activities such as respiration and digestion , it is also the locus of "higher" order functioning such as thought , reasoning , and abstraction. Generally regarded as more capable of these higher order activities, the human brain is believed to be more "intelligent" in general than that of any other known species. While some non-human species are capable of creating structures and using simple tools —mostly through instinct and mimicry—human technology is vastly more complex, and is constantly evolving and improving through time.
Humans are generally diurnal. The average sleep requirement is between seven and nine hours per day for an adult and nine to ten hours per day for a child; elderly people usually sleep for six to seven hours. Having less sleep than this is common among humans, even though sleep deprivation can have negative health effects. A sustained restriction of adult sleep to four hours per day has been shown to correlate with changes in physiology and mental state, including reduced memory, fatigue, aggression, and bodily discomfort.
In dreaming humans experience sensory images and sounds, in a sequence which the dreamer usually perceives more as an apparent participant than as an observer. Dreaming is stimulated by the pons and mostly occurs during the REM phase of sleep.
Humans are one of the relatively few species to have sufficient self-awareness to recognize themselves in a mirror. 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 physical aspects of the mind and brain, and by extension of the nervous system, are studied in the field of neurology , the more behavioral in the field of psychology, and a sometimes loosely defined area between in the field of psychiatry, which treats mental illness and behavioral 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 behavior. 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.
Psychologists have developed intelligence tests and the concept of intelligence quotient in order to assess the relative intelligence of human beings and study its distribution among population. Some philosophers divide consciousness into phenomenal consciousness, which is experience itself, and access consciousness, which is the processing of the things in experience. 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 behavior 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 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: 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 behavior, 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.
For humans, sexuality has important social functions: Sexual desire or libido , is experienced as a bodily urge, often accompanied by strong emotions such as love, ecstasy and jealousy. The significance of sexuality in the human species is reflected in a number of physical features among them hidden ovulation , the evolution of external scrotum and among great apes a relatively large penis suggesting sperm competition in humans , the absence of an os penis , permanent secondary sexual characteristics and the forming of pair bonds based on sexual attraction as a common social structure.
Contrary to other primates that often advertise estrus through visible signs, human females do not have a distinct or visible signs of ovulation, plus they experience sexual desire outside of their fertile periods. These adaptations indicate that the meaning of sexuality in humans is similar to that found in the bonobo , and that the complex human sexual behavior 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.
Humans are highly social beings and tend to live in large complex social groups. More than any other creature, humans are capable of using systems of communication for self-expression, the exchange of ideas, and organization , and as such have created complex social structures composed of many cooperating and competing groups.
Human groups range from the size of families to nations. Social interactions between humans have established an extremely wide variety [ clarification needed ] of values, social norms, and rituals, which together form the basis of human society. Culture is defined here as patterns of complex symbolic behavior, i.
While many species communicate , language is unique to humans, a defining feature of humanity, and a cultural universal. Unlike the limited systems of other animals, human language is open—an infinite number of meanings can be produced by combining a limited number of symbols. Human language also has the capacity of displacement , using words to represent things and happenings that are not presently or locally occurring, but reside in the shared imagination of interlocutors.
Language is central to the communication between humans, and to the sense of identity that unites nations, cultures and ethnic groups. The invention of writing systems at least five thousand years ago allowed the preservation of language on material objects, and was a major technological advancement.
The science of linguistics describes the structure and function of language and the relationship between languages. There are approximately six thousand different languages currently in use, including sign languages , and many thousands more that are extinct. The sexual division of humans into male, female, and in some societies other genders  has been marked culturally by a corresponding division of roles, norms, practices , dress, behavior, rights, duties , privileges , status , and power.
Cultural differences by gender have often been believed to have arisen naturally out of a division of reproductive labor; the biological fact that women give birth led to their further cultural responsibility for nurturing and caring for children.
Gender roles have varied historically, and challenges to predominant gender norms have recurred in many societies. All human societies organize, recognize and classify types of social relationships based on relations between parents and children consanguinity , and relations through marriage affinity. These kinds of relations are generally called kinship relations. In most societies kinship places mutual responsibilities and expectations of solidarity on the individuals that are so related, and those who recognize each other as kinsmen come to form networks through which other social institutions can be regulated.
Among the many functions of kinship is the ability to form descent groups , groups of people sharing a common line of descent, which can function as political units such as clans.
Another function is the way in which kinship unites families through marriage, forming kinship alliances between groups of wife-takers and wife-givers. Such alliances also often have important political and economical ramifications, and may result in the formation of political organization above the community level.
Kinship relations often includes regulations for whom an individual should or shouldn't marry. All societies have rules of incest taboo , according to which marriage between certain kinds of kin relations are prohibited—such rules vary widely between cultures. Rules and norms for marriage and social behavior among kinsfolk is often reflected in the systems of kinship terminology in the various languages of the world.
In many societies kinship relations can also be formed through forms of co-habitation, adoption, fostering, or companionship, which also tends to create relations of enduring solidarity nurture kinship. Humans often form ethnic groups, such groups tend to be larger than kinship networks and be organized around a common identity defined variously in terms of shared ancestry and history, shared cultural norms and language, or shared biological phenotype.
Such ideologies of shared characteristics are often perpetuated in the form of powerful, compelling narratives that give legitimacy and continuity to the set of shared values. Ethnic groupings often correspond to some level of political organization such as the band , tribe , city state or nation.
Although ethnic groups appear and disappear through history, members of ethnic groups often conceptualize their groups as having histories going back into the deep past. Such ideologies give ethnicity a powerful role in defining social identity and in constructing solidarity between members of an ethno-political unit. This unifying property of ethnicity has been closely tied to the rise of the nation state as the predominant form of political organization in the 19th and 20th centuries.
Society is the system of organizations and institutions arising from interaction between humans. Within a society people can be divided into different groups according to their income, wealth, power , reputation , etc. Recognition of the state's claim to independence by other states, enabling it to enter into international agreements, is often important to the establishment of its statehood.
The "state" can also be defined in terms of domestic conditions, specifically, as conceptualized by Max Weber , "a state is a human community that successfully claims the monopoly of the 'legitimate' use of physical force within a given territory. Government can be defined as the political means of creating and enforcing laws; typically via a bureaucratic hierarchy. Politics is the process by which decisions are made within groups; this process often involves conflict as well as compromise.
Although the term is generally applied to behavior within governments, politics is also observed in all human group interactions, including corporate, academic, and religious institutions.
Many different political systems exist, as do many different ways of understanding them, and many definitions overlap. Examples of governments include monarchy, Communist state , military dictatorship , theocracy , and liberal democracy , the last of which is considered dominant today.
All of these issues have a direct relationship with economics. Trade is the voluntary exchange of goods and services, and is a form of economics. A mechanism that allows trade is called a market. Modern traders instead generally negotiate through a medium of exchange, such as money. As a result, buying can be separated from selling, or earning. Because of specialization and division of labor , most people concentrate on a small aspect of manufacturing or service, trading their labor for products.
Trade exists between regions because different regions have an absolute or comparative advantage in the production of some tradable commodity, or because different regions' size allows for the benefits of mass production. Economics is a social science which studies the production, distribution, trade, and consumption of goods and services.
Economics focuses on measurable variables, and is broadly divided into two main branches: Aspects receiving particular attention in economics are resource allocation , production, distribution, trade, and competition. Economic logic is increasingly applied to any problem that involves choice under scarcity or determining economic value.
War is a state of organized armed conflict between states or non-state actors. War is characterized by the use of lethal violence against others—whether between combatants or upon non-combatants —to achieve military goals through force. Lesser, often spontaneous conflicts, such as brawls, riots , revolts , and melees , are not considered to be warfare. Revolutions can be nonviolent or an organized and armed revolution which denotes a state of war. During the 20th century, it is estimated that between and million people died as a result of war.
A war between internal elements of a state is a civil war. There have been a wide variety of rapidly advancing tactics throughout the history of war, ranging from conventional war to asymmetric warfare to total war and unconventional warfare. Techniques include hand to hand combat , the use of ranged weapons , naval warfare , and, more recently, air support. Military intelligence has often played a key role in determining victory and defeat.
Propaganda, which often includes information, slanted opinion and disinformation, plays a key role both in maintaining unity within a warring group and in sowing discord among opponents. In modern warfare , soldiers and combat vehicles are used to control the land, warships the sea, and aircraft the sky.
These fields have also overlapped in the forms of marines , paratroopers , aircraft carriers , and surface-to-air missiles , among others. Satellites in low Earth orbit have made outer space a factor in warfare as well through their use for detailed intelligence gathering; however, no known aggressive actions have been taken from space.
Stone tools were used by proto-humans at least 2. Since then, humans have made major advances, developing complex technology to create tools to aid their lives and allowing for other advancements in culture.
Major leaps in technology include the discovery of agriculture—what is known as the Neolithic Revolution , and the invention of automated machines in the Industrial Revolution. Archaeology attempts to tell the story of past or lost cultures in part by close examination of the artifacts they produced. Early humans left stone tools , pottery , and jewelry that are particular to various regions and times. Throughout history, humans have altered their appearance by wearing clothing  and adornments , by trimming or shaving hair or by means of body modifications.
Body modification is the deliberate altering of the human body for any non-medical reason, such as aesthetics, sexual enhancement, a rite of passage, religious reasons, to display group membership or affiliation, to create body art , shock value, or self-expression.
Philosophy is a discipline or field of study involving the investigation, analysis, and development of ideas at a general, abstract, or fundamental level. It is the discipline searching for a general understanding of reality, reasoning and values. Major fields of philosophy include logic , metaphysics , epistemology , philosophy of mind , and axiology which includes ethics and aesthetics.
Philosophy covers a very wide range of approaches, and is used to refer to a worldview , to a perspective on an issue, or to the positions argued for by a particular philosopher or school of philosophy.
Religion is generally defined as a belief system concerning the supernatural , sacred or divine , and practices, values , institutions and rituals associated with such belief. Some religions also have a moral code.
The evolution and the history of the first religions have recently become areas of active scientific investigation. Some of the chief questions and issues religions are concerned with include life after death commonly involving belief in an afterlife , the origin of life , the nature of the universe religious cosmology and its ultimate fate eschatology , and what is moral or immoral. A common source for answers to these questions are beliefs in transcendent divine beings such as deities or a singular God, although not all religions are theistic.
Spirituality, belief or involvement in matters of the soul or spirit , is one of the many different approaches humans take in trying to answer fundamental questions about humankind's place in the universe, the meaning of life , and the ideal way to live one's life. Though these topics have also been addressed by philosophy, and to some extent by science, spirituality is unique in that it focuses on mystical or supernatural concepts such as karma and God.
Although the exact level of religiosity can be hard to measure,  a majority of humans professes some variety of religious or spiritual belief, although many in some countries a majority are irreligious. This includes humans who have no religious beliefs or do not identify with any religion. Humanism is a philosophy which seeks to include all of humanity and all issues common to humans; it is usually non-religious.
Most religions and spiritual beliefs are clearly distinct from science on both a philosophical and methodological level; the two are not generally considered mutually exclusive and a majority of humans hold a mix of both scientific and religious views. The distinction between philosophy and religion, on the other hand, is at times less clear, and the two are linked in such fields as the philosophy of religion and theology.
Humans have been producing art works at least since the days of Cro-Magnon. Art may be defined as a form of cultural expression and the usage of narratives of liberation and exploration i. This distinction may be applied to objects or performances, current or historical, and its prestige extends to those who made, found, exhibit, or own them. In the modern use of the word, art is commonly understood to be the process or result of making material works that, from concept to creation, adhere to the "creative impulse" of human beings.
Music is a natural intuitive phenomenon based on the three distinct and interrelated organization structures of rhythm, harmony, and melody. Listening to music is perhaps the most common and universal form of entertainment, while learning and understanding it are popular disciplines.
Literature, the body of written—and possibly oral—works, especially creative ones, includes prose, poetry and drama, both fiction and non-fiction. Literature includes such genres as epic , legend, myth, ballad, and folklore. Another unique aspect of human culture and thought is the development of complex methods for acquiring knowledge through observation, quantification, and verification.
All of science can be divided into three major branches, the formal sciences e. From Wikipedia, the free encyclopedia. This article is about humans as a species. For other uses, see Human disambiguation. For the concept of human races, see Race human classification.
Man word and Names for the human species. Life timeline and Nature timeline. Homo and Homo sapiens. Anthropology , Human evolution , and Timeline of human evolution.
Archaic human admixture with modern humans , Early human migrations , Multiregional origin of modern humans , Prehistoric autopsy , and Recent African origin of modern humans. Neolithic Revolution and Cradle of civilization. History of the world. Human migration , Demography , and World population. 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.
Human physical appearance , Anatomically modern human , and Sex differences in humans. Boy and girl before puberty.
Adolescent male and female. Adult man and woman. Elderly man and woman. Childbirth , Life expectancy , and Human development biology. Venus of Willendorf statuette from the Upper Palaeolithic period. Two starved boys during the Russian famine of — Human brain and Mind. Love and Human sexuality. This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.
July Learn how and when to remove this template message. Culture , Society , and Human behavior. Gender role and Gender. Origins of society , Society , Government , Politics , and State polity. Clothing , Body modification , and Haircut. Philosophy and Human self-reflection. Art , Music , and Literature. This section does not cite any sources.
Please help improve this section by adding citations to reliable sources. March Learn how and when to remove this template message. Human portal Mammals portal. Mammal Species of the World: A Taxonomic and Geographic Reference 3rd ed. Johns Hopkins University Press.
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Archived from the original on 7 May Retrieved 4 July Archived from the original on 24 July Department of Justice, Bureau of Justice Statistics,. Archived from the original on 9 July Evolution and General Intelligence: Three hypotheses on the evolution of general intelligence Archived 13 September at the Wayback Machine. Archived from the original on 1 June Retrieved 30 May This was progressively lost in Habilines. Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, not just to the legs and pelvis, but also to the vertebral column , feet and ankles, and skull.
The knee and ankle joints became increasingly robust to better support increased weight. To support the increased weight on each vertebra in the upright position, the human vertebral column became S-shaped and the lumbar vertebrae became shorter and wider.
In the feet the big toe moved into alignment with the other toes to help in forward locomotion. The arms and forearms shortened relative to the legs making it easier to run. The foramen magnum migrated under the skull and more anterior. The most significant changes occurred in the pelvic region, where the long downward facing iliac blade was shortened and widened as a requirement for keeping the center of gravity stable while walking;  bipedal hominids have a shorter but broader, bowl-like pelvis due to this.
A drawback is that the birth canal of bipedal apes is smaller than in knuckle-walking apes, though there has been a widening of it in comparison to that of australopithecine and modern humans, permitting the passage of newborns due to the increase in cranial size but this is limited to the upper portion, since further increase can hinder normal bipedal movement.
The shortening of the pelvis and smaller birth canal evolved as a requirement for bipedalism and had significant effects on the process of human birth which is much more difficult in modern humans than in other primates.
During human birth, because of the variation in size of the pelvic region, the fetal head must be in a transverse position compared to the mother during entry into the birth canal and rotate about 90 degrees upon exit.
This brain increase manifested during postnatal brain growth , far exceeding that of other apes heterochrony. It also allowed for extended periods of social learning and language acquisition in juvenile humans, beginning as much as 2 million years ago.
Furthermore, the changes in the structure of human brains may be even more significant than the increase in size. 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.
The increase in volume of the neocortex also included a rapid increase in size of the cerebellum. Its function has traditionally been associated with balance and fine motor control, but more recently with speech and cognition.
The great apes, including hominids, had a more pronounced cerebellum relative to the neocortex than other primates. It has been suggested that because of its function of sensory-motor control and learning complex muscular actions, the cerebellum may have underpinned human technological adaptations, including the preconditions of speech.
The immediate survival advantage of encephalization is difficult to discern, as the major brain changes from Homo erectus to Homo heidelbergensis were not accompanied by major changes in technology.
It has been suggested that the changes were mainly social and behavioural, including increased empathic abilities,   increases in size of social groups,    and increased behavioural plasticity .
The reduced degree of sexual dimorphism in humans is visible primarily in the reduction of the male canine tooth relative to other ape species except gibbons and reduced brow ridges and general robustness of males. Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans are the only hominoids 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 or overt changes in proceptivity during estrus.
The ulnar opposition — the contact between the thumb and the tip of the little finger of the same hand — is unique to anatomically modern humans. A number of other changes have also characterized the evolution of humans, among them an increased importance on vision rather than smell; a longer juvenile developmental period and higher infant dependency; a smaller gut; faster basal metabolism;  loss of body hair; evolution of sweat glands; a change in the shape of the dental arcade from being u-shaped to being parabolic; development of a chin found in Homo sapiens alone ; development of styloid processes ; and the development of a descended larynx.
The word homo , the name of the biological genus to which humans belong, is Latin for "human". It was chosen originally by Carl Linnaeus in his classification system. The word "human" is from the Latin humanus , the adjectival form of homo. The possibility of linking humans with earlier apes by descent became clear only after with the publication of Charles Darwin 's On the Origin of Species , in which he argued for the idea of the evolution of new species from earlier ones.
Darwin's book did not address the question of human evolution, saying only that "Light will be thrown on the origin of man and his history. The first debates about the nature of human evolution arose between Thomas Henry Huxley and Richard Owen. Huxley argued for human evolution from apes by illustrating many of the similarities and differences between humans and apes, and did so particularly in his book Evidence as to Man's Place in Nature.
However, many of Darwin's early supporters such as Alfred Russel Wallace and Charles Lyell did not initially agree that the origin of the mental capacities and the moral sensibilities of humans could be explained by natural selection , though this later changed. Darwin applied the theory of evolution and sexual selection to humans when he published The Descent of Man in A major problem in the 19th century was the lack of fossil intermediaries.
Neanderthal remains were discovered in a limestone quarry in , three years before the publication of On the Origin of Species , and Neanderthal fossils had been discovered in Gibraltar even earlier, but it was originally claimed that these were human remains of a creature suffering some kind of illness.
The child's remains were a remarkably well-preserved tiny skull and an endocast of the brain. Also, the specimen showed short canine teeth , and the position of the foramen magnum the hole in the skull where the spine enters was evidence of bipedal locomotion. All of these traits convinced Dart that the Taung Child was a bipedal human ancestor, a transitional form between apes and humans.
During the s and s, hundreds of fossils were found in East Africa in the regions of the Olduvai Gorge and Lake Turkana. The driving force of these searches was the Leakey family, with Louis Leakey and his wife Mary Leakey , and later their son Richard and daughter-in-law Meave —all successful and world-renowned fossil hunters and paleoanthropologists. From the fossil beds of Olduvai and Lake Turkana they amassed specimens of the early hominins: These finds cemented Africa as the cradle of humankind.
In the late s and the s, Ethiopia emerged as the new hot spot of paleoanthropology after "Lucy" , the most complete fossil member of the species Australopithecus afarensis , was found in by Donald Johanson near Hadar in the desertic Afar Triangle region of northern Ethiopia. Although the specimen had a small brain, the pelvis and leg bones were almost identical in function to those of modern humans, showing with certainty that these hominins had walked erect.
White in the s, including Ardipithecus ramidus and Ardipithecus kadabba. In , fossil skeletons of Homo naledi , an extinct species of hominin assigned provisionally to the genus Homo , were found in the Rising Star Cave system, a site in South Africa 's Cradle of Humankind region in Gauteng province near Johannesburg.
The skeletal anatomy combines primitive features known from australopithecines with features known from early hominins. The individuals show signs of having been deliberately disposed of within the cave near the time of death.
The fossils have not yet been dated. The genetic revolution in studies of human evolution started when Vincent Sarich and Allan Wilson measured the strength of immunological cross-reactions of blood serum albumin between pairs of creatures, including humans and African apes chimpanzees and gorillas. By constructing a calibration curve of the ID of species' pairs with known divergence times in the fossil record, the data could be used as a molecular clock to estimate the times of divergence of pairs with poorer or unknown fossil records.
In their seminal paper in Science , Sarich and Wilson estimated the divergence time of humans and apes as four to five million years ago,  at a time when standard interpretations of the fossil record gave this divergence as at least 10 to as much as 30 million years. Subsequent fossil discoveries, notably "Lucy", and reinterpretation of older fossil materials, notably Ramapithecus , showed the younger estimates to be correct and validated the albumin method. On the basis of a separation from the orangutan between 10 and 20 million years ago, earlier studies of the molecular clock suggested that there were about 76 mutations per generation that were not inherited by human children from their parents; this evidence supported the divergence time between hominins and chimps noted above.
However, a study in Iceland of 78 children and their parents suggests a mutation rate of only 36 mutations per generation; this datum extends the separation between humans and chimps to an earlier period greater than 7 million years ago Ma. Additional research with offspring of wild chimp populations in 8 locations suggests that chimps reproduce at age And these data suggest that Ardipithecus 4.
Furthermore, analysis of the two species' genes in provides evidence that after human ancestors had started to diverge from chimpanzees, interspecies mating between "proto-human" and "proto-chimps" nonetheless occurred regularly enough to change certain genes in the new gene pool:. In the s, several teams of paleoanthropologists were working throughout Africa looking for evidence of the earliest divergence of the hominin lineage from the great apes. In , Meave Leakey discovered Australopithecus anamensis.
The find was overshadowed by Tim D. White's discovery of Ardipithecus ramidus , which pushed back the fossil record to 4. In , Martin Pickford and Brigitte Senut discovered, in the Tugen Hills of Kenya , a 6-million-year-old bipedal hominin which they named Orrorin tugenensis.
And in , a team led by Michel Brunet discovered the skull of Sahelanthropus tchadensis which was dated as 7. Anthropologists in the s were divided regarding some details of reproductive barriers and migratory dispersals of the genus Homo. Subsequently, genetics has been used to investigate and resolve these issues. According to the Sahara pump theory evidence suggests that genus Homo have migrated out of Africa at least three and possibly four times e.
Homo erectus , Homo heidelbergensis and two or three times for Homo sapiens. Recent evidence suggests these dispersals are closely related to fluctuating periods of climate change. Recent evidence suggests that humans may have left Africa half a million years earlier than previously thought. This is earlier than the previous earliest finding of genus Homo at Dmanisi , in Georgia , dating to 1.
Although controversial, tools found at a Chinese cave strengthen the case that humans used tools as far back as 2. Up until the genetic evidence became available there were two dominant models for the dispersal of modern humans. The multiregional hypothesis proposed that the genus Homo contained only a single interconnected population as it does today not separate species , and that its evolution took place worldwide continuously over the last couple of million years.
This model was proposed in by Milford H. This model has been developed by Chris B. Stringer and Peter Andrews. Sequencing mtDNA and Y-DNA sampled from a wide range of indigenous populations revealed ancestral information relating to both male and female genetic heritage, and strengthened the Out of Africa theory and weakened the views of Multiregional Evolutionism. After analysing genealogy trees constructed using types of mtDNA, researchers concluded that all were descended from a female African progenitor, dubbed Mitochondrial Eve.
A broad study of African genetic diversity, headed by Sarah Tishkoff , found the San people had the greatest genetic diversity among the distinct populations sampled, making them one of 14 " ancestral population clusters ".
The research also located a possible origin of modern human migration in south-western Africa, near the coastal border of Namibia and Angola. However, evidence for archaic admixture in modern humans , both in Africa and later, throughout Eurasia has recently been suggested by a number of studies. Recent sequencing of Neanderthal  and Denisovan  genomes shows that some admixture with these populations has occurred.
These new results do not contradict the "out of Africa" model, except in its strictest interpretation, although they make the situation more complex. After recovery from a genetic bottleneck that could possibly be due to the Toba supervolcano catastrophe , a fairly small group left Africa and later briefly interbred on three separate occasions with Neanderthals, probably in the middle-east, on the Eurasian steppe or even in North Africa before their departure.
Their still predominantly African descendants spread to populate the world. A fraction in turn interbred with Denisovans, probably in south-east Asia, before populating Melanesia. There are still differing theories on whether there was a single exodus from Africa or several.
A multiple dispersal model involves the Southern Dispersal theory,  which has gained support in recent years from genetic, linguistic and archaeological evidence. In this theory, there was a coastal dispersal of modern humans from the Horn of Africa crossing the Bab el Mandib to Yemen at a lower sea level around 70, years ago. This group helped to populate Southeast Asia and Oceania, explaining the discovery of early human sites in these areas much earlier than those in the Levant.
Stephen Oppenheimer has proposed a second wave of humans may have later dispersed through the Persian Gulf oases, and the Zagros mountains into the Middle East. Alternatively it may have come across the Sinai Peninsula into Asia, from shortly after 50, yrs BP, resulting in the bulk of the human populations of Eurasia. It has been suggested that this second group possibly possessed a more sophisticated "big game hunting" tool technology and was less dependent on coastal food sources than the original group.
Much of the evidence for the first group's expansion would have been destroyed by the rising sea levels at the end of each glacial maximum. Stephen Oppenheimer, on the basis of the early date of Badoshan Iranian Aurignacian, suggests that this second dispersal, may have occurred with a pluvial period about 50, years before the present, with modern human big-game hunting cultures spreading up the Zagros Mountains, carrying modern human genomes from Oman, throughout the Persian Gulf, northward into Armenia and Anatolia, with a variant travelling south into Israel and to Cyrenicia.
The evidence on which scientific accounts of human evolution are based comes from many fields of natural science. The main source of knowledge about the evolutionary process has traditionally been the fossil record, but since the development of genetics beginning in the s, DNA analysis has come to occupy a place of comparable importance.
The studies of ontogeny, phylogeny and especially evolutionary developmental biology of both vertebrates and invertebrates offer considerable insight into the evolution of all life, including how humans evolved.
The specific study of the origin and life of humans is anthropology , particularly paleoanthropology which focuses on the study of human prehistory. The closest living relatives of humans are bonobos and chimpanzees both genus Pan and gorillas genus Gorilla. The gibbons family Hylobatidae and then orangutans genus Pongo were the first groups to split from the line leading to the hominins, including humans—followed by gorillas, and, ultimately, by the chimpanzees genus Pan.
Genetic evidence has also been employed to resolve the question of whether there was any gene flow between early modern humans and Neanderthals , and to enhance our understanding of the early human migration patterns and splitting dates.
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 single-nucleotide polymorphism 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 , years ago.
Human evolutionary genetics studies how one human genome differs from the other, the evolutionary past that gave rise to it, and its current effects. Differences between genomes have anthropological , medical and forensic implications and applications. Genetic data can provide important insight into human evolution. There is little fossil evidence for the divergence of the gorilla, chimpanzee and hominin lineages. Each of these have been argued to be a bipedal ancestor of later hominins but, in each case, the claims have been contested.
It is also possible that one or more of these species are ancestors of another branch of African apes, or that they represent a shared ancestor between hominins and other apes. The question then of the relationship between these early fossil species and the hominin lineage is still to be resolved. The australopithecine species that is best represented in the fossil record is Australopithecus afarensis with more than one hundred fossil individuals represented, found from Northern Ethiopia such as the famous "Lucy" , to Kenya, and South Africa.
Fossils of robust australopithecines such as Au. The earliest member of the genus Homo is Homo habilis which evolved around 2. They developed the Oldowan lithic technology, named after the Olduvai Gorge in which the first specimens were found.
Some scientists consider Homo rudolfensis , a larger bodied group of fossils with similar morphology to the original H. 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, by the arrival about 1. Homo erectus were the first of the hominins to emigrate from Africa, and, from 1. One population of H. It is believed that these species, H. The earliest transitional fossils between H. These descendants of African H.
The earliest fossils of anatomically modern humans are from the Middle Paleolithic, about , years ago such as the Omo remains of Ethiopia; later fossils from Es Skhul cave in Israel and Southern Europe begin around 90, years ago 0. 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.
This migration out of Africa is estimated to have begun about 70, years BP and modern humans subsequently spread globally, replacing earlier hominins either through competition or hybridization. The hypothesis of interbreeding, also known as hybridization, admixture or hybrid-origin theory, has been discussed ever since the discovery of Neanderthal remains in the 19th century. In the 21st century with the advent of molecular biology techniques and computerization, whole-genome sequencing of Neanderthal and human genome were performed, confirming recent admixture between different human species.
It has been demonstrated that interbreeding happened in several independent events that included Neanderthals, Denisovans, as well as several unidentified hominins. For example, comparative studies in the mids found several traits related to neurological, immunological,  developmental, and metabolic phenotypes, that were developed by archaic humans to European and Asian environments and inherited to modern humans through admixture with local hominins.
Although the narratives of human evolution are often contentious, several discoveries since show that human evolution should not be seen as a simple linear or branched progression, but a mix of related species.
Evolutionary history of the primates can be traced back 65 million years. Begun  concluded that early primates flourished in Eurasia and that a lineage leading to the African apes and humans, including to Dryopithecus , migrated south from Europe or Western Asia into Africa.
The surviving tropical population of primates—which is seen most completely in the Upper Eocene and lowermost Oligocene fossil beds of the Faiyum depression southwest of Cairo —gave rise to all extant primate species, including the lemurs of Madagascar , lorises of Southeast Asia, galagos or "bush babies" of Africa, and to the anthropoids , which are the Platyrrhines or New World monkeys, the Catarrhines or Old World monkeys, and the great apes, including humans and other hominids.
The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Great Rift Valley in Kenya, dated to 24 million years ago.
In the Early Miocene , about 22 million years ago, the many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus , the earliest Old World monkey. Among the genera thought to be in the ape lineage leading up to 13 million years ago are Proconsul , Rangwapithecus , Dendropithecus , Limnopithecus , Nacholapithecus , Equatorius , Nyanzapithecus , Afropithecus , Heliopithecus , and Kenyapithecus , all from East Africa.
The presence of other generalized non-cercopithecids of Middle Miocene from sites far distant— Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France , Spain and Austria —is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the Early and Middle Miocene.
The youngest of the Miocene hominoids, Oreopithecus , is from coal beds in Italy that have been dated to 9 million years ago. Molecular evidence indicates that the lineage of gibbons family Hylobatidae diverged from the line of great apes some 18—12 million years ago, and that of orangutans subfamily Ponginae diverged from the other great apes at about 12 million years; there are no fossils that clearly document the ancestry of gibbons, which may have originated in a so-far-unknown South East Asian hominoid population, but fossil proto-orangutans may be represented by Sivapithecus from India and Griphopithecus from Turkey , dated to around 10 million years ago.
Species close to the last common ancestor of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the chimpanzees genus Pan split off from the line leading to the humans.
Human DNA is approximately The fossil record, however, of gorillas and chimpanzees is limited; both poor preservation—rain forest soils tend to be acidic and dissolve bone—and sampling bias probably contribute to this problem. Other hominins probably adapted to the drier environments outside the equatorial belt; and there they encountered antelope, hyenas, dogs, pigs, elephants, horses, and others. The equatorial belt contracted after about 8 million years ago, and there is very little fossil evidence for the split—thought to have occurred around that time—of the hominin lineage from the lineages of gorillas and chimpanzees.
The earliest fossils argued by some to belong to the human lineage are Sahelanthropus tchadensis 7 Ma and Orrorin tugenensis 6 Ma , followed by Ardipithecus 5. It has been argued in a study of the life history of Ar. It was also argued that the species provides support for the notion that very early hominins, akin to bonobos Pan paniscus the less aggressive species of chimpanzee, may have evolved via the process of self-domestication.
Consequently, arguing against the so-called "chimpanzee referential model"  the authors suggest it is no longer tenable to use common chimpanzee Pan troglodytes social and mating behaviors in models of early hominin social evolution. When commenting on the absence of aggressive canine morphology in Ar. However, the fact that Ar. In fact the trend towards increased maternal care, female mate selection and self-domestication may have been stronger and more refined in Ar.
The authors argue that many of the basic human adaptations evolved in the ancient forest and woodland ecosystems of late Miocene and early Pliocene Africa. Consequently, they argue that humans may not represent evolution from a chimpanzee-like ancestor as has traditionally been supposed. This suggests many modern human adaptations represent phylogenetically deep traits and that the behavior and morphology of chimpanzees may have evolved subsequent to the split with the common ancestor they share with humans.
The genus Australopithecus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago.
During this time period various forms of australopiths existed, including Australopithecus anamensis , Au. There is still some debate among academics whether certain African hominid species of this time, such as Au. However, if these species do indeed constitute their own genus, then they may be given their own name, the Paranthropus. A new proposed species Australopithecus deyiremeda is claimed to have been discovered living at the same time period of Au.
There is debate if Au. The earliest documented representative of the genus Homo is Homo habilis , which evolved around 2. The brains of these early hominins were about the same size as that of a chimpanzee , although it has been suggested that this was the time in which the human SRGAP2 gene doubled, producing a more rapid wiring of the frontal cortex.
It is believed that Homo erectus and Homo ergaster were the first to use fire and complex tools, and were the first of the hominin line to leave Africa, spreading throughout Africa, Asia, and Europe between 1. According to the recent African origin of modern humans theory, modern humans evolved in Africa possibly from Homo heidelbergensis , Homo rhodesiensis or Homo antecessor and migrated out of the continent some 50, to , years ago, gradually replacing local populations of Homo erectus , Denisova hominins , Homo floresiensis and Homo neanderthalensis.
Homo sapiens is the only extant species of its genus, Homo. While some extinct Homo species might have been ancestors of Homo sapiens , many, perhaps most, were likely "cousins", having speciated away from the ancestral hominin line.
Based on archaeological and paleontological evidence, it has been possible to infer, to some extent, the ancient dietary practices  of various Homo species and to study the role of diet in physical and behavioral evolution within Homo. Some anthropologists and archaeologists subscribe to the Toba catastrophe theory , which posits that the supereruption of Lake Toba on Sumatran island in Indonesia some 70, years ago caused global consequences,  killing the majority of humans and creating a population bottleneck that affected the genetic inheritance of all humans today.
Homo habilis lived from about 2. Homo habilis had smaller molars and larger brains than the australopithecines, and made tools from stone and perhaps animal bones. One of the first known hominins was nicknamed 'handy man' by discoverer Louis Leakey due to its association with stone tools. Some scientists have proposed moving this species out of Homo and into Australopithecus due to the morphology of its skeleton being more adapted to living on trees rather than to moving on two legs like Homo sapiens.
In May , a new species, Homo gautengensis , was discovered in South Africa. These are proposed species names for fossils from about 1. The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in on the Indonesian island of Java.
He originally named the material Anthropopithecus erectus , considered a this point as a chimpanzee-like fossil primate and Pithecanthropus erectus , changing his mind as of based on its morphology, which he considered to be intermediate between that of humans and apes.
Weidenreich concluded in that because of their anatomical similarity with modern humans it was necessary to gather all these specimens of Java and China in a single species of the genus Homo , the species Homo erectus. The early phase of Homo erectus , from 1. In Africa in the Early Pleistocene, 1. This species also may have used fire to cook meat. Richard Wrangham suggests that the fact that Homo seems to have been ground dwelling, with reduced intestinal length, smaller dentition, "and swelled our brains to their current, horrendously fuel-inefficient size",  suggest that control of fire and releasing increased nutritional value through cooking was the key adaptation that separated Homo from tree-sleeping Australopithecines.
Many paleoanthropologists now use the term Homo ergaster for the non-Asian forms of this group, and reserve Homo erectus only for those fossils that are found in Asia and meet certain skeletal and dental requirements which differ slightly from H. These are proposed as species that may be intermediate between H. Also proposed as Homo sapiens heidelbergensis or Homo sapiens paleohungaricus. Homo neanderthalensis , alternatively designated as Homo sapiens neanderthalensis ,  lived in Europe and Asia from ,  to about 28, years ago.
Many of these relate to the superior adaptation to cold environments possessed by the Neanderthal populations. Their surface to volume ratio is an extreme version of that found amongst Inuit populations, indicating that they were less inclined to lose body heat than were AMH. From brain Endocasts, Neanderthals also had significantly larger brains. This would seem to indicate that the intellectual superiority of AMH populations may be questionable.
Dunbar, however, have shown important differences in Brain architecture. For example, in both the orbital chamber size and in the size of the occipital lobe , the larger size suggests that the Neanderthal had a better visual acuity than modern humans.
This would give a superior vision in the inferior light conditions found in Glacial Europe. It also seems that the higher body mass of Neanderthals had a correspondingly larger brain mass required for body care and control. The Neanderthal populations seem to have been physically superior to AMH populations. These differences may have been sufficient to give Neanderthal populations an environmental superiority to AMH populations from 75, to 45, years BP. With these differences, Neanderthal brains show a smaller area was available for social functioning.
Plotting group size possible from endocrainial volume, suggests that AMH populations minus occipital lobe size , had a Dunbars number of possible relationships. Neanderthal populations seem to have been limited to about individuals.
This would show up in a larger number of possible mates for AMH humans, with increased risks of inbreeding amongst Neanderthal populations. It also suggests that humans had larger trade catchment areas than Neanderthals confirmed in the distribution of stone tools. With larger populations, social and technological innovations were easier to fix in human populations, which may have all contributed to the fact that modern Homo sapiens replaced the Neanderthal populations by 28, BP.
Earlier evidence from sequencing mitochondrial DNA suggested that no significant gene flow occurred between H. Though this interbred Romanian population seems not to have been ancestral to modern humans, the finding indicates that interbreeding happened repeatedly. In , archaeologists working at the site of Denisova Cave in the Altai Mountains of Siberia uncovered a small bone fragment from the fifth finger of a juvenile member of Denisovans.
While the divergence point of the mtDNA was unexpectedly deep in time,  the full genomic sequence suggested the Denisovans belonged to the same lineage as Neanderthals, with the two diverging shortly after their line split from the lineage that gave rise to modern humans. The existence of this distant branch creates a much more complex picture of humankind during the Late Pleistocene than previously thought. Alleles thought to have originated in Neanderthals and Denisovans have been identified at several genetic loci in the genomes of modern humans outside of Africa.
HLA haplotypes from Denisovans and Neanderthal represent more than half the HLA alleles of modern Eurasians,  indicating strong positive selection for these introgressed alleles. Corinne Simoneti at Vanderbilt University, in Nashville and her team have found from medical records of 28, people of European descent that the presence of Neanderthal DNA segments may be associated with a likelihood to suffer depression more frequently.
The flow of genes from Neanderthal populations to modern human was not all one way. Sergi Castellano of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has in reported that while Denisovan and Neanderthal genomes are more related to each other than they are to us, Siberian Neanderthal genomes show similarity to the modern human gene pool, more so than to European Neanderthal populations.
The evidence suggests that the Neanderthal populations interbred with modern humans possibly , years ago, probably somewhere in the Near East. Studies of a Neanderthal child at Gibraltar show from brain development and teeth eruption that Neanderthal children may have matured more rapidly than is the case for Homo sapiens.
In other words, H. The main find was a skeleton believed to be a woman of about 30 years of age. Found in , it has been dated to approximately 18, years old. However, there is an ongoing debate over whether H.
This, coupled with pathological dwarfism, could have resulted in a significantly diminutive human. The other major attack on H. The hypothesis of pathological dwarfism, however, fails to explain additional anatomical features that are unlike those of modern humans diseased or not but much like those of ancient members of our genus.
Aside from cranial features, these features include the form of bones in the wrist, forearm, shoulder, knees, and feet. Additionally, this hypothesis fails to explain the find of multiple examples of individuals with these same characteristics, indicating they were common to a large population, and not limited to one individual.
The direct evidence suggests there was a migration of H. A subsequent migration both within and out of Africa eventually replaced the earlier dispersed H. This migration and origin theory is usually referred to as the "recent single-origin hypothesis" or "out of Africa" theory. The Toba catastrophe theory , which postulates a population bottleneck for H. Distinctive human genetic variability has arisen as the result of the founder effect , by archaic admixture and by recent evolutionary pressures.
The use of tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution, especially the continued expansion of the human brain.
The brain of a modern human consumes about 13 watts kilocalories per day , a fifth of the body's resting power consumption. Researchers have suggested that early hominins were thus under evolutionary pressure to increase their capacity to create and use tools. Precisely when early humans started to use tools is difficult to determine, because the more primitive these tools are for example, sharp-edged stones the more difficult it is to decide whether they are natural objects or human artifacts.
Many species make and use tools , but it is the human genus that dominates the areas of making and using more complex tools. The oldest known tools are flakes from West Turkana, Kenya, which date to 3. The next oldest stone tools are from Gona, Ethiopia, and are considered the beginning of the Oldowan technology.
These tools date to about 2. A Homo fossil was found near some Oldowan tools , and its age was noted at 2. It is a possibility but does not yet represent solid evidence. It allows humans the dexterity and strength to make and use complex tools. This unique anatomical feature separates humans from apes and other nonhuman primates, and is not seen in human fossils older than 1.
Bernard Wood noted that Paranthropus co-existed with the early Homo species in the area of the "Oldowan Industrial Complex" over roughly the same span of time. Although there is no direct evidence which identifies Paranthropus as the tool makers, their anatomy lends to indirect evidence of their capabilities in this area. Most paleoanthropologists agree that the early Homo species were indeed responsible for most of the Oldowan tools found. They argue that when most of the Oldowan tools were found in association with human fossils, Homo was always present, but Paranthropus was not.
In , Randall Susman used the anatomy of opposable thumbs as the basis for his argument that both the Homo and Paranthropus species were toolmakers. He compared bones and muscles of human and chimpanzee thumbs, finding that humans have 3 muscles which are lacking in chimpanzees.
Humans also have thicker metacarpals with broader heads, allowing more precise grasping than the chimpanzee hand can perform. Susman posited that modern anatomy of the human opposable thumb is an evolutionary response to the requirements associated with making and handling tools and that both species were indeed toolmakers.
Stone tools are first attested around 2. Archaeologists working in the Great Rift Valley in Kenya have discovered the oldest known stone tools in the world. Dated to around 3. The period from ,—, years ago is also known as the Acheulean , when H. After , BP the more refined so-called Levallois technique was developed, a series of consecutive strikes, by which scrapers, slicers "racloirs" , needles, and flattened needles were made.