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154-522: In humans , the nasal cycle is the normal ultradian cycle of each nostril's blood vessels becoming engorged in swelling, then shrinking. The nostrils are separated by the septum . The septum can sometimes be deviated , causing one nostril to appear larger than the other. With extreme damage to the septum and columella, the two nostrils are no longer separated and form a single larger external opening. Like other tetrapods , humans have two external nostrils (anterior nares) and two additional nostrils at

308-415: A multi-layered network of cooperating, distinct, or even competing social groups – from families and peer groups to corporations and political states . As such, social interactions between humans have established a wide variety of values, social norms , languages , and traditions (collectively termed institutions ), each of which bolsters human society . Humans are also highly curious , with

462-668: A theory of mind . The human mind is capable of introspection , private thought , imagination , volition , and forming views on existence . This has allowed great technological advancements and complex tool development through complex reasoning and the transmission of knowledge to subsequent generations through language . Humans have had a dramatic effect on the environment . They are apex predators , being rarely preyed upon by other species. Human population growth , industrialization, land development, overconsumption and combustion of fossil fuels have led to environmental destruction and pollution that significantly contributes to

616-442: A 395-million-year-old fossilized fish which shows this migration in progress. It has two nostrils between its front teeth, similar to human embryos at an early stage. If these fail to join up, the result is a cleft palate . Each external nostril contains approximately 1,000 strands of nasal hair , which function to filter foreign particles such as pollen and dust. It is possible for humans to smell different olfactory inputs in

770-407: A belief if this belief is to amount to knowledge. When the belief is challenged, the person may justify it by referring to their reason for holding it. In many cases, this reason depends itself on another belief that may as well be challenged. An example is a person who believes that Ford cars are cheaper than BMWs. When their belief is challenged, they may justify it by claiming that they heard it from

924-474: A belief is involved. The main controversy surrounding this definition concerns its third feature: justification. This component is often included because of the impression that some true beliefs are not forms of knowledge, such as beliefs based on superstition , lucky guesses, or erroneous reasoning . For example, a person who guesses that a coin flip will land heads usually does not know that even if their belief turns out to be true. This indicates that there

1078-461: A broad social phenomenon that is similar to culture. The term may further denote knowledge stored in documents like the "knowledge housed in the library" or the knowledge base of an expert system . Knowledge is closely related to intelligence , but intelligence is more about the ability to acquire, process, and apply information, while knowledge concerns information and skills that a person already possesses. The word knowledge has its roots in

1232-405: A complex web of interconnected ideas that is justified by its coherence rather than by a few privileged foundational beliefs. One difficulty for this view is how to demonstrate that it does not involve the fallacy of circular reasoning . If two beliefs mutually support each other then a person has a reason for accepting one belief if they already have the other. However, mutual support alone is not

1386-443: A consequence of better nutrition, healthcare, and living conditions. The average mass of an adult human is 59 kg (130 lb) for females and 77 kg (170 lb) for males. Like many other conditions, body weight and body type are influenced by both genetic susceptibility and environment and varies greatly among individuals. Humans have a far faster and more accurate throw than other animals. Humans are also among

1540-573: A controlled experiment to compare whether predictions based on the hypothesis match the observed results. As a last step, the results are interpreted and a conclusion is reached whether and to what degree the findings confirm or disconfirm the hypothesis. The empirical sciences are usually divided into natural and social sciences . The natural sciences, like physics , biology , and chemistry , focus on quantitative research methods to arrive at knowledge about natural phenomena. Quantitative research happens by making precise numerical measurements and

1694-488: A cup of coffee made by a reliable coffee machine has the same value as an equally good cup of coffee made by an unreliable coffee machine. This difficulty in solving the value problem is sometimes used as an argument against reliabilism. Virtue epistemology, by contrast, offers a unique solution to the value problem. Virtue epistemologists see knowledge as the manifestation of cognitive virtues. They hold that knowledge has additional value due to its association with virtue. This

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1848-419: A few other places), saw the emergence of agriculture and permanent human settlement ; in turn, this led to the development of civilization and kickstarted a period of continuous (and ongoing) population growth and rapid technological change . Since then, a number of civilizations have risen and fallen, while a number of sociocultural and technological developments have resulted in significant changes to

2002-519: A form of inevitable ignorance that can affect both what is knowable about the external world as well as what one can know about oneself and about what is good. Some limits of knowledge only apply to particular people in specific situations while others pertain to humanity at large. A fact is unknowable to a person if this person lacks access to the relevant information, like facts in the past that did not leave any significant traces. For example, it may be unknowable to people today what Caesar 's breakfast

2156-477: A good reason for newly accepting both beliefs at once. A closely related issue is that there can be distinct sets of coherent beliefs. Coherentists face the problem of explaining why someone should accept one coherent set rather than another. For infinitists, in contrast to foundationalists and coherentists, there is an infinite number of reasons. This view embraces the idea that there is a regress since each reason depends on another reason. One difficulty for this view

2310-463: A great capacity for altering their habitats by means of technology, irrigation , urban planning , construction, deforestation and desertification . Human settlements continue to be vulnerable to natural disasters , especially those placed in hazardous locations and with low quality of construction. Grouping and deliberate habitat alteration is often done with the goals of providing protection, accumulating comforts or material wealth, expanding

2464-612: A higher body fat percentage. At puberty , humans develop secondary sex characteristics . Females are capable of pregnancy , usually between puberty, at around 12 years old, and menopause , around the age of 50. As omnivorous creatures, they are capable of consuming a wide variety of plant and animal material, and have used fire and other forms of heat to prepare and cook food since the time of Homo erectus . Humans can survive for up to eight weeks without food and several days without water . Humans are generally diurnal , sleeping on average seven to nine hours per day. Childbirth

2618-475: A human can lose personhood (such as by going into a persistent vegetative state ). Humans are apes ( superfamily Hominoidea ). The lineage of apes that eventually gave rise to humans first split from gibbons (family Hylobatidae) and orangutans (genus Pongo ), then gorillas (genus Gorilla ), and finally, chimpanzees and bonobos (genus Pan ). The last split, between the human and chimpanzee–bonobo lineages, took place around 8–4 million years ago, in

2772-430: A letter, a newspaper, or a blog . The problem of testimony consists in clarifying why and under what circumstances testimony can lead to knowledge. A common response is that it depends on the reliability of the person pronouncing the testimony: only testimony from reliable sources can lead to knowledge. The problem of the limits of knowledge concerns the question of which facts are unknowable . These limits constitute

2926-581: A more barrel-shaped chests in contrast to the funnel shape of other apes, an adaptation for bipedal respiration. Apart from bipedalism and brain size, humans differ from chimpanzees mostly in smelling , hearing and digesting proteins . While humans have a density of hair follicles comparable to other apes, it is predominantly vellus hair , most of which is so short and wispy as to be practically invisible. Humans have about 2 million sweat glands spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on

3080-566: A more explicit structure and is not articulated in terms of universal ideas. The term is often used in feminism and postmodernism to argue that many forms of knowledge are not absolute but depend on the concrete historical, cultural, and linguistic context. Explicit knowledge is knowledge that can be fully articulated, shared, and explained, like the knowledge of historical dates and mathematical formulas. It can be acquired through traditional learning methods, such as reading books and attending lectures. It contrasts with tacit knowledge , which

3234-504: A much clearer picture of life at the time. Between the 8th and 6th century BCE, Europe entered the classical antiquity age, a period when ancient Greece and ancient Rome flourished. Around this time other civilizations also came to prominence. The Maya civilization started to build cities and create complex calendars . In Africa, the Kingdom of Aksum overtook the declining Kingdom of Kush and facilitated trade between India and

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3388-469: A negative sense: many see it as a serious challenge to any epistemological theory and often try to show how their preferred theory overcomes it. Another form of philosophical skepticism advocates the suspension of judgment as a form of attaining tranquility while remaining humble and open-minded . A less radical limit of knowledge is identified by fallibilists , who argue that the possibility of error can never be fully excluded. This means that even

3542-489: A negative value. For example, if a person's life depends on gathering the courage to jump over a ravine, then having a true belief about the involved dangers may hinder them from doing so. Besides having instrumental value, knowledge may also have intrinsic value . This means that some forms of knowledge are good in themselves even if they do not provide any practical benefits. According to philosopher Duncan Pritchard , this applies to forms of knowledge linked to wisdom . It

3696-519: A pain or to confuse the experience of a slight ellipse for the experience of a circle. Perceptual and introspective knowledge often act as a form of fundamental or basic knowledge. According to some empiricists , they are the only sources of basic knowledge and provide the foundation for all other knowledge. Memory differs from perception and introspection in that it is not as independent or basic as they are since it depends on other previous experiences. The faculty of memory retains knowledge acquired in

3850-520: A person knows that cats have whiskers then this knowledge is dispositional most of the time and becomes occurrent while they are thinking about it. Many forms of Eastern spirituality and religion distinguish between higher and lower knowledge. They are also referred to as para vidya and apara vidya in Hinduism or the two truths doctrine in Buddhism . Lower knowledge is based on the senses and

4004-556: A practically useful characterization. Another approach, termed analysis of knowledge , tries to provide a theoretically precise definition by listing the conditions that are individually necessary and jointly sufficient , similar to how chemists analyze a sample by seeking a list of all the chemical elements composing it. According to a different view, knowledge is a unique state that cannot be analyzed in terms of other phenomena. Some scholars base their definition on abstract intuitions while others focus on concrete cases or rely on how

4158-472: A practice that aims to produce habits of action. There is still very little consensus in the academic discourse as to which of the proposed modifications or reconceptualizations is correct, and there are various alternative definitions of knowledge . A common distinction among types of knowledge is between propositional knowledge, or knowledge-that, and non-propositional knowledge in the form of practical skills or acquaintance. Other distinctions focus on how

4312-468: A priori knowledge exists as innate knowledge present in the mind of each human. A further approach posits a special mental faculty responsible for this type of knowledge, often referred to as rational intuition or rational insight. Various other types of knowledge are discussed in the academic literature. In philosophy, "self-knowledge" refers to a person's knowledge of their own sensations , thoughts , beliefs, and other mental states. A common view

4466-442: A proposition, one has to be acquainted with its constituents. The distinction between a priori and a posteriori knowledge depends on the role of experience in the processes of formation and justification. To know something a posteriori means to know it based on experience. For example, by seeing that it rains outside or hearing that the baby is crying, one acquires a posteriori knowledge of these facts. A priori knowledge

4620-536: A reliable source. This justification depends on the assumption that their source is reliable, which may itself be challenged. The same may apply to any subsequent reason they cite. This threatens to lead to an infinite regress since the epistemic status at each step depends on the epistemic status of the previous step. Theories of the structure of knowledge offer responses for how to solve this problem. Three traditional theories are foundationalism , coherentism , and infinitism . Foundationalists and coherentists deny

4774-451: A result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforest , arid desert , extremely cold arctic regions , and heavily polluted cities; in comparison, most other species are confined to a few geographical areas by their limited adaptability. The human population is not, however, uniformly distributed on the Earth 's surface, because

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4928-639: A similar species. Migrating out of Africa , they gradually replaced and interbred with local populations of archaic humans. Multiple hypotheses for the extinction of archaic human species such as Neanderthals include competition, violence , interbreeding with Homo sapiens , or inability to adapt to climate change . Humans began exhibiting behavioral modernity about 160,000–60,000 years ago. For most of their history, humans were nomadic hunter-gatherers. The Neolithic Revolution , which began in Southwest Asia around 13,000 years ago (and separately in

5082-515: A simple linear or branched progression but involved interbreeding between related species . Genomic research has shown that hybridization between substantially diverged lineages was common in human evolution. DNA evidence suggests that several genes of Neanderthal origin are present among all non sub-Saharan-African populations, and Neanderthals and other hominins, such as Denisovans , may have contributed up to 6% of their genome to present-day non sub-Saharan-African humans. Human evolution

5236-414: A slightly different sense, self-knowledge can also refer to knowledge of the self as a persisting entity with certain personality traits , preferences , physical attributes, relationships, goals, and social identities . Metaknowledge is knowledge about knowledge. It can arise in the form of self-knowledge but includes other types as well, such as knowing what someone else knows or what information

5390-405: A specific domain and is only possessed by experts. Situated knowledge is knowledge specific to a particular situation. It is closely related to practical or tacit knowledge, which is learned and applied in specific circumstances. This especially concerns certain forms of acquiring knowledge, such as trial and error or learning from experience. In this regard, situated knowledge usually lacks

5544-451: A successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times greater than in developed countries. Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care

5698-427: A sufficient degree of coherence among all the mental states of the believer is necessary for knowledge. According to infinitism, an infinite chain of beliefs is needed. The main discipline investigating knowledge is epistemology , which studies what people know, how they come to know it, and what it means to know something. It discusses the value of knowledge and the thesis of philosophical skepticism , which questions

5852-423: A that-clause. Propositional knowledge takes the form of mental representations involving concepts, ideas, theories, and general rules. These representations connect the knower to certain parts of reality by showing what they are like. They are often context-independent, meaning that they are not restricted to a specific use or purpose. Propositional knowledge encompasses both knowledge of specific facts, like that

6006-406: A wide variety of plant and animal material. Human groups have adopted a range of diets from purely vegan to primarily carnivorous . In some cases, dietary restrictions in humans can lead to deficiency diseases ; however, stable human groups have adapted to many dietary patterns through both genetic specialization and cultural conventions to use nutritionally balanced food sources. The human diet

6160-471: Is perception , which involves the usage of the senses to learn about the external world. Introspection allows people to learn about their internal mental states and processes. Other sources of knowledge include memory , rational intuition , inference , and testimony . According to foundationalism , some of these sources are basic in that they can justify beliefs, without depending on other mental states. Coherentists reject this claim and contend that

6314-511: Is 38 weeks, but a normal pregnancy can vary by up to 37 days. Embryonic development in the human covers the first eight weeks of development; at the beginning of the ninth week the embryo is termed a fetus . Humans are able to induce early labor or perform a caesarean section if the child needs to be born earlier for medical reasons. In developed countries, infants are typically 3–4 kg (7–9 lb) in weight and 47–53 cm (19–21 in) in height at birth. However, low birth weight

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6468-485: 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. Genes and environment influence human biological variation in visible characteristics, physiology, disease susceptibility and mental abilities. The exact influence of genes and environment on certain traits

6622-424: Is a population decline in the winter months of this realm. Humans established nation-states in the other seven realms, such as South Africa , India , Russia , Australia , Fiji , United States and Brazil (each located in a different biogeographical realm). By using advanced tools and clothing , humans have been able to extend their tolerance to a wide variety of temperatures, humidities , and altitudes. As

6776-461: Is a widely accepted feature of knowledge. It implies that, while it may be possible to believe something false, one cannot know something false. That knowledge is a form of belief implies that one cannot know something if one does not believe it. Some everyday expressions seem to violate this principle, like the claim that "I do not believe it, I know it!" But the point of such expressions is usually to emphasize one's confidence rather than denying that

6930-434: Is able to pass that exam or by knowing which horse is the fastest, one can earn money from bets. In these cases, knowledge has instrumental value . Not all forms of knowledge are useful and many beliefs about trivial matters have no instrumental value. This concerns, for example, knowing how many grains of sand are on a specific beach or memorizing phone numbers one never intends to call. In a few cases, knowledge may even have

7084-411: Is already true. The problem of the value of knowledge is often discussed in relation to reliabilism and virtue epistemology . Reliabilism can be defined as the thesis that knowledge is reliably formed true belief. This view has difficulties in explaining why knowledge is valuable or how a reliable belief-forming process adds additional value. According to an analogy by philosopher Linda Zagzebski ,

7238-420: Is also referred to as knowledge-that , as in "Akari knows that kangaroos hop". In this case, Akari stands in the relation of knowing to the proposition "kangaroos hop". Closely related types of knowledge are know-wh , for example, knowing who is coming to dinner and knowing why they are coming. These expressions are normally understood as types of propositional knowledge since they can be paraphrased using

7392-564: Is an active process in which sensory signals are selected, organized, and interpreted to form a representation of the environment. This leads in some cases to illusions that misrepresent certain aspects of reality, like the Müller-Lyer illusion and the Ponzo illusion . Introspection is often seen in analogy to perception as a source of knowledge, not of external physical objects, but of internal mental states . A traditionally common view

7546-552: Is applied to draw inferences from other known facts. For example, the perceptual knowledge of a Czech stamp on a postcard may give rise to the inferential knowledge that one's friend is visiting the Czech Republic. This type of knowledge depends on other sources of knowledge responsible for the premises. Some rationalists argue for rational intuition as a further source of knowledge that does not rely on observation and introspection. They hold for example that some beliefs, like

7700-528: Is argued that there is no perceptual knowledge of the external world. This thought experiment is based on the problem of underdetermination , which arises when the available evidence is not sufficient to make a rational decision between competing theories. In such cases, a person is not justified in believing one theory rather than the other. If this is always the case then global skepticism follows. Another skeptical argument assumes that knowledge requires absolute certainty and aims to show that all human cognition

7854-512: Is at home". Other types of knowledge include knowledge-how in the form of practical competence , as in "she knows how to swim", and knowledge by acquaintance as a familiarity with the known object based on previous direct experience, like knowing someone personally. Knowledge is often understood as a state of an individual person, but it can also refer to a characteristic of a group of people as group knowledge, social knowledge, or collective knowledge. Some social sciences understand knowledge as

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8008-401: Is based on the idea that cognitive success in the form of the manifestation of virtues is inherently valuable independent of whether the resulting states are instrumentally useful. Acquiring and transmitting knowledge often comes with certain costs, such as the material resources required to obtain new information and the time and energy needed to understand it. For this reason, an awareness of

8162-427: Is called epistemology or the theory of knowledge. It examines the nature of knowledge and justification, how knowledge arises, and what value it has. Further topics include the different types of knowledge and the limits of what can be known. Despite agreements about the general characteristics of knowledge, its exact definition is disputed. Some definitions only focus on the most salient features of knowledge to give

8316-402: 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 hairlessness , obligate bipedalism, increased brain size and decreased sexual dimorphism ( neoteny ). The relationship between all these changes

8470-412: Is circular and requires interpretation, which implies that knowledge does not need a secure foundation. Coherentists and infinitists avoid these problems by denying the contrast between basic and non-basic reasons. Coherentists argue that there is only a finite number of reasons, which mutually support and justify one another. This is based on the intuition that beliefs do not exist in isolation but form

8624-456: Is common in developing countries, and contributes to the high levels of infant mortality in these regions. Compared with other species, human childbirth is dangerous, with a much higher risk of complications and death. The size of the fetus's head is more closely matched to the pelvis than in other primates. The reason for this is not completely understood, but it contributes to a painful labor that can last 24 hours or more. The chances of

8778-608: Is contained in a scientific article. Other aspects of metaknowledge include knowing how knowledge can be acquired, stored, distributed, and used. Common knowledge is knowledge that is publicly known and shared by most individuals within a community. It establishes a common ground for communication, understanding, social cohesion, and cooperation. General knowledge encompasses common knowledge but also includes knowledge that many people have been exposed to but may not be able to immediately recall. Common knowledge contrasts with domain knowledge or specialized knowledge, which belongs to

8932-460: Is controversial whether all knowledge has intrinsic value, including knowledge about trivial facts like knowing whether the biggest apple tree had an even number of leaves yesterday morning. One view in favor of the intrinsic value of knowledge states that having no belief about a matter is a neutral state and knowledge is always better than this neutral state, even if the value difference is only minimal. A more specific issue in epistemology concerns

9086-421: Is dangerous, with a high risk of complications and death . Often, both the mother and the father provide care for their children, who are helpless at birth . Humans have a large, highly developed, and complex prefrontal cortex , the region of the brain associated with higher cognition. Humans are highly intelligent and capable of episodic memory ; they have flexible facial expressions, self-awareness , and

9240-453: Is fallible since it fails to meet this standard. An influential argument against radical skepticism states that radical skepticism is self-contradictory since denying the existence of knowledge is itself a knowledge-claim. Other arguments rely on common sense or deny that infallibility is required for knowledge. Very few philosophers have explicitly defended radical skepticism but this position has been influential nonetheless, usually in

9394-479: Is generally aging, with the median age around 40 years. In the developing world , the median age is between 15 and 20 years. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older. In 2012, the United Nations estimated that there were 316,600 living centenarians (humans of age 100 or older) worldwide. Humans are omnivorous , capable of consuming

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9548-409: Is impossible, meaning that one cannot know what is morally good or whether a certain behavior is morally right. An influential theory about the limits of metaphysical knowledge was proposed by Immanuel Kant . For him, knowledge is restricted to the field of appearances and does not reach the things in themselves , which exist independently of humans and lie beyond the realm of appearances. Based on

9702-443: 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 90,000 to 200,000 years ago. Most human reproduction takes place by internal fertilization via sexual intercourse , but can also occur through assisted reproductive technology procedures. The average gestation period

9856-415: Is knowledge acquired because of specific social and cultural circumstances, such as knowing how to read and write. Knowledge can be occurrent or dispositional . Occurrent knowledge is knowledge that is actively involved in cognitive processes. Dispositional knowledge, by contrast, lies dormant in the back of a person's mind and is given by the mere ability to access the relevant information. For example, if

10010-553: Is more to knowledge than just being right about something. These cases are excluded by requiring that beliefs have justification for them to count as knowledge. Some philosophers hold that a belief is justified if it is based on evidence , which can take the form of mental states like experience, memory , and other beliefs. Others state that beliefs are justified if they are produced by reliable processes, like sensory perception or logical reasoning. The definition of knowledge as justified true belief came under severe criticism in

10164-408: Is mostly done by the mother. Helpless at birth , humans continue to grow for some years, typically reaching sexual maturity at 15 to 17 years of age. The human life span has been split into various stages ranging from three to twelve. Common stages include infancy , childhood , adolescence , adulthood and old age . The lengths of these stages have varied across cultures and time periods but

10318-472: Is not aware of this, stops in front of the real barn by a lucky coincidence, and forms the justified true belief that they are in front of a barn. This example aims to establish that the person does not know that they are in front of a real barn, since they would not have been able to tell the difference. This means that it is a lucky coincidence that this justified belief is also true. According to some philosophers, these counterexamples show that justification

10472-552: Is not easily articulated or explained to others, like the ability to recognize someone's face and the practical expertise of a master craftsman. Tacit knowledge is often learned through first-hand experience or direct practice. Cognitive load theory distinguishes between biologically primary and secondary knowledge. Biologically primary knowledge is knowledge that humans have as part of their evolutionary heritage, such as knowing how to recognize faces and speech and many general problem-solving capacities. Biologically secondary knowledge

10626-415: Is not possible to know them because if a person knew about such an idea then this idea would have occurred at least to them. There are many disputes about what can or cannot be known in certain fields. Religious skepticism is the view that beliefs about God or other religious doctrines do not amount to knowledge. Moral skepticism encompasses a variety of views, including the claim that moral knowledge

10780-453: Is not required for knowledge and that knowledge should instead be characterized in terms of reliability or the manifestation of cognitive virtues . Another approach defines knowledge in regard to the function it plays in cognitive processes as that which provides reasons for thinking or doing something. A different response accepts justification as an aspect of knowledge and include additional criteria. Many candidates have been suggested, like

10934-521: Is not well understood. While no humans – not even monozygotic twins  – are genetically identical, two humans on average will have a genetic similarity of 99.5%-99.9%. This makes them more homogeneous than other great apes, including chimpanzees. This small variation in human DNA compared to many other species suggests a population bottleneck during the Late Pleistocene (around 100,000 years ago), in which

11088-404: Is possible without any experience to justify or support the known proposition. Mathematical knowledge, such as that 2 + 2 = 4, is traditionally taken to be a priori knowledge since no empirical investigation is necessary to confirm this fact. In this regard, a posteriori knowledge is empirical knowledge while a priori knowledge is non-empirical knowledge. The relevant experience in question

11242-446: Is primarily identified with sensory experience . Some non-sensory experiences, like memory and introspection, are often included as well. Some conscious phenomena are excluded from the relevant experience, like rational insight. For example, conscious thought processes may be required to arrive at a priori knowledge regarding the solution of mathematical problems, like when performing mental arithmetic to multiply two numbers. The same

11396-415: Is prominently reflected in human culture and has led to the development of food science . Knowledge Knowledge is an awareness of facts , a familiarity with individuals and situations , or a practical skill . Knowledge of facts, also called propositional knowledge, is often characterized as true belief that is distinct from opinion or guesswork by virtue of justification . While there

11550-414: Is public, reliable, and replicable. This way, other researchers can repeat the experiments and observations in the initial study to confirm or disconfirm it. The scientific method is often analyzed as a series of steps that begins with regular observation and data collection. Based on these insights, scientists then try to find a hypothesis that explains the observations. The hypothesis is then tested using

11704-404: Is that inquiry should not aim for truth or absolute certainty but for well-supported and justified beliefs while remaining open to the possibility that one's beliefs may need to be revised later. The structure of knowledge is the way in which the mental states of a person need to be related to each other for knowledge to arise. A common view is that a person has to have good reasons for holding

11858-413: Is that introspection has a special epistemic status by being infallible. According to this position, it is not possible to be mistaken about introspective facts, like whether one is in pain, because there is no difference between appearance and reality. However, this claim has been contested in the contemporary discourse and critics argue that it may be possible, for example, to mistake an unpleasant itch for

12012-472: Is that self-knowledge is more direct than knowledge of the external world, which relies on the interpretation of sense data. Because of this, it is traditionally claimed that self-knowledge is indubitable, like the claim that a person cannot be wrong about whether they are in pain. However, this position is not universally accepted in the contemporary discourse and an alternative view states that self-knowledge also depends on interpretations that could be false. In

12166-414: Is that the human mind is limited and may not be able to possess an infinite number of reasons. This raises the question of whether, according to infinitism, human knowledge is possible at all. Knowledge may be valuable either because it is useful or because it is good in itself. Knowledge can be useful by helping a person achieve their goals. For example, if one knows the answers to questions in an exam one

12320-442: Is the case for the experience needed to learn the words through which the claim is expressed. For example, knowing that "all bachelors are unmarried" is a priori knowledge because no sensory experience is necessary to confirm this fact even though experience was needed to learn the meanings of the words "bachelor" and "unmarried". It is difficult to explain how a priori knowledge is possible and some empiricists deny it exists. It

12474-445: Is the subject of ongoing debate. Hylobatidae ( gibbons ) Pongo abelii Pongo tapanuliensis Pongo pygmaeus Gorilla gorilla Gorilla beringei Pan troglodytes Pan paniscus Homo sapiens (humans) Until about 12,000 years ago, all humans lived as hunter-gatherers . The Neolithic Revolution (the invention of agriculture ) first took place in Southwest Asia and spread through large parts of

12628-654: Is typified by an unusually rapid growth spurt during adolescence. Human females undergo menopause and become infertile at around the age of 50. 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. The life span of an individual depends on two major factors, genetics and lifestyle choices. For various reasons, including biological/genetic causes, women live on average about four years longer than men. As of 2018 ,

12782-402: Is usually seen as unproblematic that one can come to know things through experience, but it is not clear how knowledge is possible without experience. One of the earliest solutions to this problem comes from Plato , who argues that the soul already possesses the knowledge and just needs to recollect, or remember, it to access it again. A similar explanation is given by Descartes , who holds that

12936-530: Is wide agreement among philosophers that propositional knowledge is a form of true belief, many controversies focus on justification. This includes questions like how to understand justification, whether it is needed at all, and whether something else besides it is needed. These controversies intensified in the latter half of the 20th century due to a series of thought experiments called Gettier cases that provoked alternative definitions. Knowledge can be produced in many ways. The main source of empirical knowledge

13090-548: The British Empire expanded to become the world's largest empire . A tenuous balance of power among European nations collapsed in 1914 with the outbreak of the First World War , one of the deadliest conflicts in history. In the 1930s, a worldwide economic crisis led to the rise of authoritarian regimes and a Second World War , involving almost all of the world's countries . The war's destruction led to

13244-580: The Caral–Supe civilization is the oldest complex civilization in the Americas. Astronomy and mathematics were also developed and the Great Pyramid of Giza was built. There is evidence of a severe drought lasting about a hundred years that may have caused the decline of these civilizations, with new ones appearing in the aftermath. Babylonians came to dominate Mesopotamia while others, such as

13398-511: The Church would provide centralized authority and education. In the Middle East, Islam became the prominent religion and expanded into North Africa. It led to an Islamic Golden Age , inspiring achievements in architecture , the revival of old advances in science and technology, and the formation of a distinct way of life. The Christian and Islamic worlds would eventually clash, with

13552-474: The Homo genus. The name " Homo sapiens " means 'wise man' or 'knowledgeable man'. There is disagreement if certain extinct members of the genus, namely Neanderthals , should be included as a separate species of humans or as a subspecies of H. sapiens . Human is a loanword of Middle English from Old French humain , ultimately from Latin hūmānus , the adjectival form of homō ('man' – in

13706-579: The Kingdom of England , the Kingdom of France and the Holy Roman Empire declaring a series of holy wars to regain control of the Holy Land from Muslims . In the Americas, between 200 and 900 CE Mesoamerica was in its Classic Period , while further north, complex Mississippian societies would arise starting around 800 CE. The Mongol Empire would conquer much of Eurasia in the 13th and 14th centuries. Over this same time period,

13860-854: The Mali Empire in Africa grew to be the largest empire on the continent, stretching from Senegambia to Ivory Coast . Oceania would see the rise of the Tuʻi Tonga Empire which expanded across many islands in the South Pacific. By the late 15th century, the Aztecs and Inca had become the dominant power in Mesoamerica and the Andes , respectively. The early modern period in Europe and

14014-587: The Old World over the following millennia. It also occurred independently in Mesoamerica (about 6,000 years ago), China, Papua New Guinea , and the Sahel and West Savanna regions of Africa. 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

14168-652: The Poverty Point culture , Minoans and the Shang dynasty , rose to prominence in new areas. The Late Bronze Age collapse around 1200 BCE resulted in the disappearance of a number of civilizations and the beginning of the Greek Dark Ages . During this period iron started replacing bronze, leading to the Iron Age . In the 5th century BCE, history started being recorded as a discipline , which provided

14322-795: The colonization of the Americas and the Columbian Exchange . This expansion led to the Atlantic slave trade and the genocide of Native American peoples . This period also marked the Scientific Revolution , with great advances in mathematics , mechanics , astronomy and physiology . The late modern period (1800–present) saw the Technological and Industrial Revolution bring such discoveries as imaging technology , major innovations in transport and energy development . Influenced by Enlightenment ideals,

14476-438: The knowledge of one's own existence and the content of one's ideas. The view that basic reasons exist is not universally accepted. One criticism states that there should be a reason why some reasons are basic while others are not. According to this view, the putative basic reasons are not actually basic since their status would depend on other reasons. Another criticism is based on hermeneutics and argues that all understanding

14630-469: The senses , is identified as the most important source of empirical knowledge. Knowing that a baby is sleeping is observational knowledge if it was caused by a perception of the snoring baby. However, this would not be the case if one learned about this fact through a telephone conversation with one's spouse. Perception comes in different modalities, including vision , sound , touch , smell , and taste , which correspond to different physical stimuli . It

14784-565: The 12th-century Old English word cnawan , which comes from the Old High German word gecnawan . The English word includes various meanings that some other languages distinguish using several words. In ancient Greek, for example, four important terms for knowledge were used: epistēmē (unchanging theoretical knowledge), technē (expert technical knowledge), mētis (strategic knowledge), and gnōsis (personal intellectual knowledge). The main discipline studying knowledge

14938-463: The 20th century, when epistemologist Edmund Gettier formulated a series of counterexamples. They purport to present concrete cases of justified true beliefs that fail to constitute knowledge. The reason for their failure is usually a form of epistemic luck: the beliefs are justified but their justification is not relevant to the truth. In a well-known example, someone drives along a country road with many barn facades and only one real barn. The person

15092-518: The Americas and Europe experienced a period of political revolutions known as the Age of Revolution . The Napoleonic Wars raged through Europe in the early 1800s, Spain lost most of its colonies in the New World , while Europeans continued expansion into Africa  – where European control went from 10% to almost 90% in less than 50 years  – and Oceania. In the 19th century,

15246-876: The Mediterranean. In West Asia, the Achaemenid Empire 's system of centralized governance became the precursor to many later empires, while the Gupta Empire in India and the Han dynasty in China have been described as golden ages in their respective regions. Following the fall of the Western Roman Empire in 476, Europe entered the Middle Ages . During this period, Christianity and

15400-832: The Near East ( c.  1450 –1800) began with the final defeat of the Byzantine Empire , and the rise of the Ottoman Empire . Meanwhile, Japan entered the Edo period , the Qing dynasty rose in China and the Mughal Empire ruled much of India. Europe underwent the Renaissance , starting in the 15th century, and the Age of Discovery began with the exploring and colonizing of new regions. This included

15554-432: The abilities responsible for knowledge-how involve forms of knowledge-that, as in knowing how to prove a mathematical theorem, but this is not generally the case. Some types of knowledge-how do not require a highly developed mind, in contrast to propositional knowledge, and are more common in the animal kingdom. For example, an ant knows how to walk even though it presumably lacks a mind sufficiently developed to represent

15708-425: The atomic mass of gold is 196.97 u , and generalities, like that the color of leaves of some trees changes in autumn. Because of the dependence on mental representations, it is often held that the capacity for propositional knowledge is exclusive to relatively sophisticated creatures, such as humans. This is based on the claim that advanced intellectual capacities are needed to believe a proposition that expresses what

15862-478: The available food, improving aesthetics , increasing knowledge or enhancing the exchange of resources. Humans are one of the most adaptable species, despite having a low or narrow tolerance for many of the earth's extreme environments. Currently the species is present in all eight biogeographical realms , although their presence in the Antarctic realm is very limited to research stations and annually there

16016-439: The back of the nasal cavity, inside the head (posterior nares, posterior nasal apertures or choanae ). They also connect the nose to the throat (the nasopharynx), aiding in respiration. Though all four nostrils were on the outside of the head of the aquatic ancestors of modern tetrapods, the nostrils for outgoing water (excurrent nostrils) migrated to the inside of the mouth, as evidenced by the discovery of Kenichthys campbelli ,

16170-413: The behavior of genes , neutrinos , and black holes . A key aspect of most forms of science is that they seek natural laws that explain empirical observations. Scientific knowledge is discovered and tested using the scientific method . This method aims to arrive at reliable knowledge by formulating the problem in a clear way and by ensuring that the evidence used to support or refute a specific theory

16324-561: The best long-distance runners in the animal kingdom, but slower over short distances. Humans' thinner body hair and more productive sweat glands help avoid heat exhaustion while running for long distances. Compared to other apes, the human heart produces greater stroke volume and cardiac output and the aorta is proportionately larger. Like most animals, humans are a diploid and 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

16478-433: The best-researched scientific theories and the most fundamental common-sense views could still be subject to error. Further research may reduce the possibility of being wrong, but it can never fully exclude it. Some fallibilists reach the skeptical conclusion from this observation that there is no knowledge but the more common view is that knowledge exists but is fallible. Pragmatists argue that one consequence of fallibilism

16632-665: The collapse of most global empires, leading to widespread decolonization. Following the conclusion of the Second World War in 1945, the United States and the USSR emerged as the remaining global superpowers . This led to a Cold War that saw a struggle for global influence, including a nuclear arms race and a space race , ending in the collapse of the Soviet Union. The current Information Age , spurred by

16786-787: The combined eastern and western Roman Empire in the 4th century AD. Bubonic plagues , first recorded in the 6th century AD, reduced the population by 50%, with the Black Death killing 75–200 million people in Eurasia and North Africa alone. Human population is believed to have reached one billion in 1800. It has since then increased exponentially, reaching two billion in 1930 and three billion in 1960, four in 1975, five in 1987 and six billion in 1999. It passed seven billion in 2011 and passed eight billion in November 2022. It took over two million years of human prehistory and history for

16940-478: The continent, gradually replacing or interbreeding with local populations of archaic humans. Humans began exhibiting behavioral modernity about 160,000–70,000 years ago, and possibly earlier. This development was likely selected amidst natural climate change in Middle to Late Pleistocene Africa. The "out of Africa" migration took place in at least two waves, the first around 130,000 to 100,000 years ago,

17094-525: The corresponding proposition. Knowledge by acquaintance is familiarity with something that results from direct experiential contact. The object of knowledge can be a person, a thing, or a place. For example, by eating chocolate, one becomes acquainted with the taste of chocolate, and visiting Lake Taupō leads to the formation of knowledge by acquaintance of Lake Taupō. In these cases, the person forms non-inferential knowledge based on first-hand experience without necessarily acquiring factual information about

17248-421: The course of history. Knowledge is a form of familiarity, awareness , understanding , or acquaintance. It often involves the possession of information learned through experience and can be understood as a cognitive success or an epistemic contact with reality, like making a discovery. Many academic definitions focus on propositional knowledge in the form of believing certain facts, as in "I know that Dave

17402-423: The desire to understand and influence phenomena having motivated humanity's development of science , technology , philosophy , mythology , religion , and other frameworks of knowledge ; humans also study themselves through such domains as anthropology , social science , history , psychology , and medicine . There are estimated to be more than eight billion living humans . Although some scientists equate

17556-516: The development of the Internet and Artificial Intelligence systems, sees the world becoming 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. Modern humans, however, have

17710-640: The early 20th century, there has been continuous human presence in Antarctica through research stations and, since 2000, in space through habitation on the International Space Station . All modern humans are classified into the species Homo sapiens , coined by Carl Linnaeus in his 1735 work Systema Naturae . The generic name " Homo " is a learned 18th-century derivation from Latin homō , which refers to humans of either sex. The word human can refer to all members of

17864-685: The emergence of early civilizations . An urban revolution took place in the 4th millennium BCE with the development of city-states , particularly Sumerian cities located in Mesopotamia . It was in these cities that the earliest known form of writing, cuneiform script , appeared around 3000 BCE. Other major civilizations to develop around this time were Ancient Egypt and the Indus Valley Civilisation . They eventually traded with each other and invented technology such as wheels, plows and sails. Emerging by 3000 BCE,

18018-406: The existence of an infinite regress, in contrast to infinitists. According to foundationalists, some basic reasons have their epistemic status independent of other reasons and thereby constitute the endpoint of the regress. Some foundationalists hold that certain sources of knowledge, like perception, provide basic reasons. Another view is that this role is played by certain self-evident truths, like

18172-566: The genomes of 1,184 individuals from 11 populations and identified 1.6 million single nucleotide polymorphisms . African populations harbor the highest number of private genetic variants. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers that are private to these regions, especially Oceania and the Americas . By 2010 estimates, humans have approximately 22,000 genes. By comparing mitochondrial DNA , which

18326-595: The global average life expectancy at birth of a girl is estimated to be 74.9 years compared to 70.4 for a boy. There are significant geographical variations in human life expectancy, mostly correlated with economic development – for example, life expectancy at birth in Hong Kong is 87.6 years for girls and 81.8 for boys, while in the Central African Republic , it is 55.0 years for girls and 50.6 for boys. The developed world

18480-443: The human lifestyle. Genes and the environment influence human biological variation in visible characteristics, physiology , disease susceptibility, mental abilities, body size, and life span. Though humans vary in many traits, humans are among the least genetically diverse species. Any two humans are at least 99.5% genetically similar. Humans are sexually dimorphic : generally, males have greater body strength and females have

18634-555: The human population to reach one billion and only 207 years more to grow to 7 billion. The combined biomass of the carbon of all the humans on Earth in 2018 was estimated at 60 million tons, about 10 times larger than that of all non-domesticated mammals. In 2018, 4.2 billion humans (55%) lived in urban areas, up from 751 million in 1950. The most urbanized regions are Northern America (82%), Latin America (81%), Europe (74%) and Oceania (68%), with Africa and Asia having nearly 90% of

18788-517: The human population was reduced to a small number of breeding pairs. The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years. The human genome was first sequenced in 2001 and by 2020 hundreds of thousands of genomes had been sequenced. In 2012 the International HapMap Project had compared

18942-441: The intellect. It encompasses both mundane or conventional truths as well as discoveries of the empirical sciences. Higher knowledge is understood as knowledge of God, the absolute , the true self , or the ultimate reality . It belongs neither to the external world of physical objects nor to the internal world of the experience of emotions and concepts. Many spiritual teachings stress the importance of higher knowledge to progress on

19096-470: The knowledge is acquired and on the content of the known information. Propositional knowledge, also referred to as declarative and descriptive knowledge, is a form of theoretical knowledge about facts, like knowing that "2 + 2 = 4". It is the paradigmatic type of knowledge in analytic philosophy . Propositional knowledge is propositional in the sense that it involves a relation to a proposition. Since propositions are often expressed through that-clauses, it

19250-567: The late Miocene epoch. During this split, chromosome 2 was formed from the joining of two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. Following their split with chimpanzees and bonobos, the hominins diversified into many species and at least two distinct genera. All but one of these lineages – representing the genus Homo and its sole extant species Homo sapiens  – are now extinct. The genus Homo evolved from Australopithecus . Though fossils from

19404-412: The limits of knowledge is radical or global skepticism , which holds that humans lack any form of knowledge or that knowledge is impossible. For example, the dream argument states that perceptual experience is not a source of knowledge since dreaming provides unreliable information and a person could be dreaming without knowing it. Because of this inability to discriminate between dream and perception, it

19558-408: The mathematical belief that 2 + 2 = 4, are justified through pure reason alone. Testimony is often included as an additional source of knowledge that, unlike the other sources, is not tied to one specific cognitive faculty. Instead, it is based on the idea that one person can come to know a fact because another person talks about this fact. Testimony can happen in numerous ways, like regular speech,

19712-564: The military, which relies on intelligence to identify and prevent threats. In the field of education, the value of knowledge can be used to choose which knowledge should be passed on to the students. The scientific approach is usually regarded as an exemplary process of how to gain knowledge about empirical facts. Scientific knowledge includes mundane knowledge about easily observable facts, for example, chemical knowledge that certain reactants become hot when mixed together. It also encompasses knowledge of less tangible issues, like claims about

19866-501: The most common and widespread species of primate , and the last surviving species of the genus Homo . They are great apes characterized by their hairlessness , bipedalism , and high intelligence . Humans have large brains , enabling more advanced cognitive skills that enable them to thrive and adapt in varied environments, develop highly complex tools , and form complex social structures and civilizations . Humans are highly social , with individual humans tending to belong to

20020-451: The nostrils accompanied by the baring of the upper teeth is often referred to as "doing the nostrils." The Procellariiformes are distinguished from other birds by having tubular extensions of their nostrils. Widely-spaced nostrils, like those of the hammerhead shark , may be useful in determining the direction of an odour's source. Human Humans ( Homo sapiens , meaning "thinking man" or "wise man") or modern humans are

20174-420: The object. By contrast, it is also possible to indirectly learn a lot of propositional knowledge about chocolate or Lake Taupō by reading books without having the direct experiential contact required for knowledge by acquaintance. The concept of knowledge by acquaintance was first introduced by Bertrand Russell . He holds that knowledge by acquaintance is more basic than propositional knowledge since to understand

20328-421: The observation that metaphysics aims to characterize the things in themselves, he concludes that no metaphysical knowledge is possible, like knowing whether the world has a beginning or is infinite . There are also limits to knowledge in the empirical sciences, such as the uncertainty principle , which states that it is impossible to know the exact magnitudes of certain certain pairs of physical properties, like

20482-559: The ongoing mass extinction of other forms of life. Within the last century, humans have explored challenging environments such as Antarctica , the deep sea , and outer space . Human habitation within these hostile environments is restrictive and expensive, typically limited in duration, and restricted to scientific , military , or industrial expeditions. Humans have visited the Moon and made their presence known on other celestial bodies through human-made robotic spacecraft . Since

20636-442: 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 third molars , with some individuals having them congenitally absent. Humans share with chimpanzees a vestigial tail, appendix , flexible shoulder joints, grasping fingers and opposable thumbs . Humans also have

20790-474: The palm of the hand and on the soles of the feet. It is estimated that the worldwide average height for an adult human male is about 171 cm (5 ft 7 in), while the worldwide average height for adult human females is about 159 cm (5 ft 3 in). Shrinkage of stature may begin in middle age in some individuals but tends to be typical in the extremely aged . Throughout history, human populations have universally become taller, probably as

20944-503: The past and makes it accessible in the present, as when remembering a past event or a friend's phone number. It is generally seen as a reliable source of knowledge. However, it can be deceptive at times nonetheless, either because the original experience was unreliable or because the memory degraded and does not accurately represent the original experience anymore. Knowledge based on perception, introspection, and memory may give rise to inferential knowledge, which comes about when reasoning

21098-515: The population density varies from one region to another, and large stretches of surface are almost completely uninhabited, like Antarctica and vast swathes of the ocean. Most humans (61%) live in Asia; the remainder live in the Americas (14%), Africa (14%), Europe (11%), and Oceania (0.5%). Estimates of the population at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. Around 50–60 million people lived in

21252-416: The position and momentum of a particle, at the same time. Other examples are physical systems studied by chaos theory , for which it is not practically possible to predict how they will behave since they are so sensitive to initial conditions that even the slightest of variations may produce a completely different behavior. This phenomenon is known as the butterfly effect . The strongest position about

21406-702: The possibility of knowledge. Knowledge is relevant to many fields like the sciences , which aim to acquire knowledge using the scientific method based on repeatable experimentation , observation , and measurement . Various religions hold that humans should seek knowledge and that God or the divine is the source of knowledge. The anthropology of knowledge studies how knowledge is acquired, stored, retrieved, and communicated in different cultures. The sociology of knowledge examines under what sociohistorical circumstances knowledge arises, and what sociological consequences it has. The history of knowledge investigates how knowledge in different fields has developed, and evolved, in

21560-467: The question of whether or why knowledge is more valuable than mere true belief. There is wide agreement that knowledge is usually good in some sense but the thesis that knowledge is better than true belief is controversial. An early discussion of this problem is found in Plato's Meno in relation to the claim that both knowledge and true belief can successfully guide action and, therefore, have apparently

21714-399: The requirements that the justified true belief does not depend on any false beliefs, that no defeaters are present, or that the person would not have the belief if it was false. Another view states that beliefs have to be infallible to amount to knowledge. A further approach, associated with pragmatism , focuses on the aspect of inquiry and characterizes knowledge in terms of what works as

21868-479: The same value. For example, it seems that mere true belief is as effective as knowledge when trying to find the way to Larissa . According to Plato, knowledge is better because it is more stable. Another suggestion is that knowledge gets its additional value from justification. One difficulty for this view is that while justification makes it more probable that a belief is true, it is not clear what additional value it provides in comparison to an unjustified belief that

22022-404: The second ( Southern Dispersal ) around 70,000 to 50,000 years ago. H. sapiens proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000 years ago, Australia around 65,000 years ago, the Americas around 15,000 years ago, and remote islands such as Hawaii , Easter Island , Madagascar , and New Zealand in the years 300 to 1280 CE. Human evolution was not

22176-547: The sense of humanity). The native English term man can refer to the species generally (a synonym for humanity ) as well as to human males. It may also refer to individuals of either sex. Despite the fact that the word animal is colloquially used as an antonym for human , and contrary to a common biological misconception , humans are animals . The word person is often used interchangeably with human , but philosophical debate exists as to whether personhood applies to all humans or all sentient beings , and further if

22330-588: The spiritual path and to see reality as it truly is beyond the veil of appearances . Sources of knowledge are ways in which people come to know things. They can be understood as cognitive capacities that are exercised when a person acquires new knowledge. Various sources of knowledge are discussed in the academic literature, often in terms of the mental faculties responsible. They include perception, introspection, memory, inference, and testimony. However, not everyone agrees that all of them actually lead to knowledge. Usually, perception or observation, i.e. using one of

22484-433: The term "humans" with all members of the genus Homo , in common usage it generally refers to Homo sapiens , the only extant member. All other members of the genus Homo , which are now extinct, are known as archaic humans , and the term "modern human" is used to distinguish Homo sapiens from archaic humans. Anatomically modern humans emerged around 300,000 years ago in Africa, evolving from Homo heidelbergensis or

22638-405: The term is used in ordinary language . There is also disagreement about whether knowledge is a rare phenomenon that requires high standards or a common phenomenon found in many everyday situations. An often-discussed definition characterizes knowledge as justified true belief. This definition identifies three essential features: it is (1) a belief that is (2) true and (3) justified . Truth

22792-427: The transition are scarce, the earliest members of Homo share several key traits with Australopithecus . The earliest record of Homo is the 2.8 million-year-old specimen LD 350-1 from Ethiopia , and the earliest named species are Homo habilis and Homo rudolfensis which evolved by 2.3 million years ago. H. erectus (the African variant is sometimes called H. ergaster ) evolved 2 million years ago and

22946-410: The two nostrils and experience a perceptual rivalry akin to that of binocular rivalry when there are two different inputs to the two eyes. Furthermore, scent information from the two nostrils leads to two types of neural activity with the first cycle corresponding to the ipsilateral and the second cycle corresponding to the contralateral odor representations. In some cultures the extreme wide flaring of

23100-438: The value of knowledge is crucial to many fields that have to make decisions about whether to seek knowledge about a specific matter. On a political level, this concerns the problem of identifying the most promising research programs to allocate funds. Similar concerns affect businesses, where stakeholders have to decide whether the cost of acquiring knowledge is justified by the economic benefits that this knowledge may provide, and

23254-405: The world is like. Non-propositional knowledge is knowledge in which no essential relation to a proposition is involved. The two most well-known forms are knowledge-how (know-how or procedural knowledge ) and knowledge by acquaintance. To possess knowledge-how means to have some form of practical ability , skill, or competence , like knowing how to ride a bicycle or knowing how to swim. Some of

23408-440: The world's 3.4 billion rural population. Problems for humans living in cities include various forms of pollution and crime , especially in inner city and suburban slums . Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology. The dental formula of humans is: 2.1.2.3 2.1.2.3 . Humans have proportionately shorter palates and much smaller teeth than other primates. They are

23562-529: Was the day he was assassinated but it was knowable to him and some contemporaries. Another factor restricting knowledge is given by the limitations of the human cognitive faculties. Some people may lack the cognitive ability to understand highly abstract mathematical truths and some facts cannot be known by any human because they are too complex for the human mind to conceive. A further limit of knowledge arises due to certain logical paradoxes . For instance, there are some ideas that will never occur to anyone. It

23716-402: Was the first archaic human species to leave Africa and disperse across Eurasia. H. erectus also was the first to evolve a characteristically human body plan . Homo sapiens emerged in Africa around 300,000 years ago from a species commonly designated as either H. heidelbergensis or H. rhodesiensis , the descendants of H. erectus that remained in Africa. H. sapiens migrated out of

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