Human evolution

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University of California Press. Archived from the original on 2 January Until about 12, years ago the beginning of the Holocene , all humans lived as hunter-gatherers , generally in small nomadic groups known as band societies , often in caves. This section needs additional citations for verification. 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.


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 , and are the only extant species to clothe themselves and create and use numerous other technologies and arts. Humans are uniquely adept at using systems of symbolic communication such as language and art for self-expression and the exchange of ideas, and for organizing themselves into purposeful groups.

Humans create complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established an extremely wide variety of values, [10] social norms , and rituals , which together form the basis of human society. Curiosity and the human desire to understand and influence the environment and to explain and manipulate phenomena or events has provided the foundation for developing science, philosophy, mythology , religion, anthropology , and numerous other fields of knowledge.

Though most of human existence has been sustained by hunting and gathering in band societies , [11] increasing numbers of human societies began to practice sedentary agriculture approximately some 10, years ago, [12] domesticating plants and animals, thus allowing for the growth of civilization.

These human societies subsequently expanded in size, establishing various forms of government, religion, and culture around the world, unifying people within regions to form 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 increased lifespans, causing the human population to rise exponentially.

Today the global human population is estimated by the United Nations to be near 7. In common usage, the word "human" generally refers to the only extant species of the genus Homo —anatomically and behaviorally modern Homo sapiens. In scientific terms, the meanings of " hominid " and " hominin " have changed during the recent decades with advances in the discovery and study of the fossil ancestors of modern humans.

The previously clear boundary between humans and apes has blurred, resulting in now acknowledging the hominids as encompassing multiple species , and Homo and close relatives since the split from chimpanzees as the only hominins. There is also a distinction between anatomically modern humans and Archaic Homo sapiens , the earliest fossil members of the species. The species binomial " Homo sapiens " was coined by Carl Linnaeus in his 18th-century work Systema Naturae.

Note that the Latin word homo refers to humans of either gender, and that " sapiens " is the singular form while there is no such word as " sapien ". The genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids great apes 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 ,—60, years ago, [19] [20] Australia around 40, years ago, the Americas around 15, years ago, and remote islands such as Hawaii, Easter Island , Madagascar , and New Zealand between the years and The closest living relatives of humans are chimpanzees genus Pan and gorillas genus Gorilla.

The gibbons family 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 genus Pan. The splitting date between human and chimpanzee lineages is placed around 4—8 million years ago during the late Miocene epoch. There is little fossil evidence for the divergence of the gorilla, chimpanzee and hominin lineages. Each of these species has been argued to be a bipedal ancestor of later hominins, but all such claims are contested.

It is also possible that any one of the three is an ancestor of another branch of African apes, or is an ancestor shared between hominins and other African Hominoidea apes. The question of the relation between these early fossil species and the hominin lineage is still to be resolved. The earliest members of the genus Homo are Homo habilis which evolved around 2.

More recently, however, in , stone tools , perhaps predating Homo habilis , have been discovered in northwestern Kenya that have been dated to 3. 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. One population of H. It is believed that these species were the first to use fire and complex tools. 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 and the fossils of Herto sometimes classified as Homo sapiens idaltu.

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. The relationship between all these changes is the subject of ongoing debate.

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 [40] or Orrorin , with Ardipithecus , a full bipedal, [41] coming somewhat later.

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.

However, the differences between the structure of human brains and those of other apes may be even more significant than differences in size. 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.

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.

By the beginning of the Upper Paleolithic period 50, BP , full behavioral modernity , including language , music and other cultural universals had developed. Since , evidence for gene flow between archaic and modern humans during the period of roughly , to 30, years ago has been discovered. This includes modern human admixture in Neanderthals, Neanderthal admixture in modern humans, [54] [55] Denisova hominin admixture in Melanesians [56] as well as repeated admixture from unnamed archaic humans to Sub-Saharan African populations.

The "out of Africa" migration of Homo sapiens took place in at least two waves, the first around , to , years ago, the second Southern Dispersal around 70, to 60, years ago, resulting in the colonization of Australia around 65, years ago, [58] This recent out of Africa migration derived from East African populations, which had become separated from populations migrating to Southern, Central and Western Africa at least , years earlier.

They inhabited Eurasia and Oceania by 40, years ago, and the Americas at least 14, years ago. Until about 12, years ago the beginning of the Holocene , all humans lived as hunter-gatherers , generally in small nomadic groups known as band societies , often in caves. The Neolithic Revolution the invention of agriculture took place beginning about 10, years ago, first in the Fertile Crescent , spreading through large parts of the Old World over the following millennia, and independently in Mesoamerica about 6, years ago.

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 and sedentary lifestyle led to the emergence of early civilizations the development of urban developent , complex society , social stratification and writing from about 5, years ago the Bronze Age.

Only a limited set of human populations participated in the progression to historicity , substantial parts of the world remaining in a Neolithic, Mesolithic or Upper Paleolithic stage of development until the advent of globalisation and modernity initiated by European exploration and colonialism. The Scientific Revolution , Technological Revolution and the Industrial Revolution up until the 19th century resulted in independent discoveries such as imaging technology , major innovations in transport, such as the airplane and automobile; energy development , such as coal and electricity.

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. 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 [ citation needed ] , but human settlements continue to be vulnerable to natural disasters , especially those placed in hazardous locations and characterized by lack of quality of construction. 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 six of the Earth 's seven continents and adapt to virtually all climates. However the human population is not uniformly distributed on the Earth 's surface, because the population density varies from one region to another and there are large areas almost completely uninhabited, like Antarctica.

With a population of over seven billion, humans are among the most numerous of the large mammals. 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. As of September , 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 31 October Since , the human population has increased from one billion [79] to over seven billion. In , some 2. In February , the U.

Both overall population numbers and the proportion residing in cities are expected to increase significantly in the coming decades. Humans have had a dramatic effect on the environment. Humans are apex predators , being rarely preyed upon by other species. 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 trillion 10 14 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 lymphatic , the musculoskeletal , the reproductive , the respiratory , and the urinary system. Humans, like most of the other apes , lack external tails , 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. One difference is that humans have a far faster and more accurate throw than other animals.

Humans are also among the best long-distance runners in the animal kingdom, but slower over short distances. 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 usually require help from their conspecifics other members of their own species 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.

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 other 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. Although humans appear hairless compared to other primates, with notable hair growth occurring chiefly on the top of the head, underarms and pubic area , the average human has more hair follicles on his or her body than the average chimpanzee.

The main distinction is that human hairs are shorter, finer, and less heavily pigmented than the average chimpanzee's, thus making them harder to see. The dental formula of humans is: 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. 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 , 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, genes. The nucleotide diversity between humans is about 0.

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 90, to , years ago. Human accelerated regions , first described in August , [] [] are a set of 49 segments of the human genome that are conserved throughout vertebrate evolution but are strikingly different in humans.

They are named according to their degree of difference between humans and their nearest animal relative chimpanzees HAR1 showing the largest degree of human-chimpanzee differences. Found by scanning through genomic databases of multiple species, some of these highly mutated areas may contribute to human-specific traits. 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, years.

As with other mammals, human reproduction takes place as internal fertilization by sexual intercourse. During this process, the male inserts his erect penis into the female's vagina and 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.

In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately times greater than in developed countries. Females continue to develop physically until around the age of 18, whereas male development continues until around age The human life span can be split into a number of stages: The lengths of these stages, however, have varied across cultures and time periods.

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 in turn their children the grandmother hypothesis , rather than by continuing to bear children into old age.

Evidence-based studies indicate that the life span of an individual depends on two major factors, genetics and lifestyle choices. Humans are omnivorous , capable of consuming a wide variety of plant and animal material. 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.

Until the development of agriculture approximately 10, 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. 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.

The types of food consumed, and the way in which they are prepared, have 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 starvation. No two humans—not even monozygotic twins —are genetically identical. Genes and environment influence human biological variation from visible characteristics to physiology to disease susceptibility to mental abilities.

The exact influence of genes and environment on certain traits is not well understood. Most current genetic and archaeological evidence supports a recent single origin of modern humans in East Africa, [] with first migrations placed at 60, years ago. Compared to the great apes , human gene sequences —even among African populations—are remarkably homogeneous.

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. 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. 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.

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 [34] 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, [89] 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. In this period they also started to make tools out of bone.

Until about 50,—40, years ago, the use of stone tools seems to have progressed stepwise. Currently paleoanthropologists are debating whether these Homo species possessed some or many of the cultural and behavioral traits associated with modern humans such as language, complex symbolic thinking, technological creativity etc.

It seems that they were culturally conservative maintaining simple technologies and foraging patterns over very long periods. Around 50, BP, modern human culture started to evolve more rapidly. The transition to behavioral modernity has been characterized by most as a Eurasian "Great Leap Forward", [] or as the "Upper Palaeolithic Revolution", [] due to the sudden appearance of distinctive signs of modern behavior and big game hunting [93] in the archaeological record. Some other scholars consider the transition to have been more gradual, noting that some features had already appeared among archaic African Homo sapiens since , years ago.

Modern humans started burying their dead, using animal hides to make clothing, hunting with more sophisticated techniques such as using trapping pits or driving animals off cliffs , and engaging in cave painting.

Among concrete examples of modern human behavior , anthropologists include specialization of tools, use of jewellery and images such as cave drawings , organization of living space, rituals for example, burials with grave gifts , specialized hunting techniques, exploration of less hospitable geographical areas, and barter trade networks.

Debate continues as to whether a "revolution" led to modern humans "the big bang of human consciousness" , or whether the evolution was more "gradual". Evolution has continued in anatomically modern human populations, which are affected by both natural selection and genetic drift. Although selection pressure on some traits, such as resistance to smallpox, has decreased in modern human life, humans are still undergoing natural selection for many other traits.

Some of these are due to specific environmental pressures, while others are related to lifestyle changes since the development of agriculture 10, years ago , urban civilization 5, , and industrialization years ago. It has been argued that human evolution has accelerated since the development of agriculture 10, years ago and civilization some 5, years ago, resulting, it is claimed, in substantial genetic differences between different current human populations.

Particularly conspicuous is variation in superficial characteristics, such as Afro-textured hair , or the recent evolution of light skin and blond hair in some populations, which are attributed to differences in climate. Particularly strong selective pressures have resulted in high-altitude adaptation in humans , with different ones in different isolated populations. Studies of the genetic basis show that some developed very recently, with Tibetans evolving over 3, years to have high proportions of an allele of EPAS1 that is adaptive to high altitudes.

Other evolution is related to endemic diseases: For example, the population at risk of the severe debilitating disease kuru has significant over-representation of an immune variant of the prion protein gene GV versus non-immune alleles. The frequency of this genetic variant is due to the survival of immune persons. Recent human evolution related to agriculture includes genetic resistance to infectious disease that has appeared in human populations by crossing the species barrier from domesticated animals, [] as well as changes in metabolism due to changes in diet, such as lactase persistence.

In contemporary times, since industrialization, some trends have been observed: This list is in chronological order across the table by genus. Please see articles for more information. From Wikipedia, the free encyclopedia. Life timeline and Nature timeline. A global mapping model of human migration, based from divergence of the mitochondrial DNA which indicates the matrilineage.

A "trellis" as Milford H. Wolpoff called it that emphasizes back-and-forth gene flow among geographic regions. Different models for the beginning of the present human species. Early human migrations , Recent African origin of modern humans , Multiregional origin of modern humans , and Early hominids in Southeast Asia. Human evolutionary genetics and Human genetic variation. Interbreeding between archaic and modern humans. For evolutionary history before primates, see Evolution of mammals , Evolutionary history of life , and Timeline of human evolution.

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