Main articles: Race and Ethnic group
Humans often categorize themselves in terms of race or ethnicity, although the scientific validity of human races as categories is disputed. Human racial categories are based on both ancestry and visible traits, especially skin color and facial features. Ethnic groups, on the other hand, are more often linked by linguistic, cultural, and national or regional ties. Self-identification with an ethnic group is based on kinship and descent. Race and ethnicity can lead to variant treatment and impact social identity, giving rise to the theory of identity politics.
Although most humans recognize that variances occur within a species, it is often a point of dispute as to what these differences entail, their importance, and whether discrimination based on race (racism) is acceptable. Some societies have placed a great deal of emphasis on race, while others have not.[citation needed]
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Evolution
Main article: Human evolution
Reconstructed skull of Peking Man, a representative of the extinct species believed to be the nearest ancestor of Homo sapiens, Homo erectus.The study of human evolution encompasses the development of the genus Homo, but usually involves studying other hominids and hominines as well, such as the australopithecines. "Modern humans" are defined as the Homo sapiens species, of which the only extant subspecies is Homo sapiens sapiens; Homo sapiens idaltu (roughly translated as "elder wise man"), the other known subspecies, is extinct.[12]
The closest living relatives of Homo sapiens are the Common Chimpanzee and the Bonobo. Full genome sequencing resulted in the conclusion that "After 6.5 [million] years of separate evolution, the differences between chimpanzee and human are just 10 times greater than those between two unrelated people and 10 times less than those between rats and mice." In fact, chimpanzee and human DNA is 96% identical.[13] It has been estimated that the human lineage diverged from that of chimpanzees about five million years ago, and from gorillas about eight million years ago. However, a hominid skull discovered in Chad in 2001, classified as Sahelanthropus tchadensis, is approximately seven million years old, which may indicate an earlier divergence.
There are two prominent scientific theories of the origins of contemporary humans. They concern the relationship between modern humans and other hominids. The single-origin, or "out of Africa", hypothesis proposes that modern humans evolved in Africa and later migrated outwards to replace hominids in other parts of the world. The multiregional hypothesis, on the other hand, proposes that modern humans evolved, at least in part, from independent hominid populations.[14]
Geneticists Lynn Jorde and Henry Harpending of the University of Utah proposed that the variation in human DNA is minute compared to that of other species, and that during the Late Pleistocene, the human population was reduced to a small number of breeding pairs—no more than 10,000—resulting in a very small residual gene pool. Various reasons for this hypothetical bottleneck have been postulated, the most popular being the Toba catastrophe theory.
Human evolution is characterized by a number of important physiological trends, including the expansion of the brain cavity and brain itself, which is typically 1,400 cm³ in volume, over twice that of a chimpanzee or gorilla. The pattern of human postnatal brain growth differs from that of other apes (heterochrony), allowing for an extended period of social learning in juvenile humans. Physical anthropologists argue that a reorganization of the structure of the brain is more important than cranial expansion itself. Other significant evolutionary changes included a reduction of the canine tooth, development of bipedal locomotion, and the descent of the larynx and hyoid bone, making speech possible. How these trends are related and what their role is in the evolution of complex social organization and culture are matters of ongoing debate in the field of physical anthropology.[15][16]
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Habitat and population
Main articles: Demography and World population
Map of early human migrations according to mitochondrial population genetics (The arctic is at the centre of the map and the numbers are millennia before present).The most widely accepted view among current anthropologists is that Homo sapiens originated in the African savanna between 200,000 and 250,000 years ago, descending from Homo erectus, and colonized Eurasia and Oceania by 40,000 years ago, and finally colonized the Americas by 10,000 years ago.[17] They displaced Homo neanderthalensis, Homo floresiensis and other species descended from Homo erectus (which had colonized Eurasia as early as 2 million years ago) through more successful reproduction and competition for resources.
The earliest humans were hunter-gatherers, a lifestyle well-suited to the savanna. Some later groups of humans were nomads, often to facilitate animal herding, and still later humans established permanent settlements, which was made possible by the development of agriculture. Permanent human settlements were dependent on proximity to water and, depending on the lifestyle, other natural resources, such as fertile land for growing crops and grazing livestock, or seasonally by hunting populations of prey. However, humans have a great capacity for altering their habitats by various methods, such as through irrigation, urban planning, construction, transport, and manufacturing goods, and with the advent of large-scale trade and transport infrastructure, proximity to these resources has become unnecessary, and in many places these factors are no longer a driving force behind the growth and decline of a population. Nonetheless, the manner in which a habitat is altered is often a major determinant in population change.
Technology has allowed humans to colonize all of the continents and adapt to all climates. Within the last few decades, humans have explored Antarctica, the ocean depths, and space, although long-term habitation of these environments is not yet possible. With a population of over six billion, humans are among the most numerous of the large mammals. Most humans (61%) live in Asia. The vast majority of the remainder live in the Americas (14%), Africa (13%) and Europe (12%), with 0.5% in Oceania. (See list of countries by population and list of countries by population density.)
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. Between 1969 and 1972, two humans at a time spent brief intervals on the Moon. As of 2006, no other celestial body has been visited by human beings, although there has been a continuous human presence in space since the launch of the initial crew to inhabit the International Space Station on October 31, 2000.
From AD 1800 to 2000, the human population increased from one to six billion. In 2004, around 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas, and this percentage is expected to rise throughout the 21st century. Problems for humans living in cities include various forms of pollution, crime[verification needed], and poverty[verification needed], especially in inner city and suburban slums. Benefits of urban living include increased literacy, access to the global cannon of human knowledge and decreased susceptibility to rural famines.
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Diet
Fruit marketThe human diet, similar to most mammals, centers around regular intake of food and drink. It is prominently reflected in human culture, and has led to the development of food science. Failure to obtain food leads to hunger and eventually starvation, while failure to obtain water leads to thirst and dehydration. Both starvation and dehydration cause death if not alleviated. 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. In modern times, obesity among some human populations has increased to almost epidemic proportions, leading to health complications and increased mortality in some developed, and, increasingly, in developing countries. The United States Center for Disease Control states that 32% of adults over the age of 20 are obese, while 66.5% are obese or overweight. Obesity is believed to be caused by a number of factors, with many attributing excessive weight gain to overeating.
Humans are animals who can consume both plant and animal products. Most biologists agree humans are omnivorous.[18] A minority believes they are an anatomically herbivorous species, many members of which have begun consuming food of animal origin.[19] Another minority believes that anatomically, they are primarily carnivorous, and have started using agriculture only recently.[20] Early Homo sapiens employed a "hunter-gatherer" methodology as their primary means of food collection, involving combining stationary plant and fungal food sources (such as fruits, grains, tubers, and mushrooms) with wild game which must be hunted and killed in order to be consumed. Some humans choose to be vegans or vegetarians, abstaining from eating meat for religious, ethical, ecological, or health reasons. It is believed that humans have used fire to prepare and cook food prior to eating since the time of their divergence from Homo erectus—possibly even earlier. However, a small number of individuals choose a raw foodist approach, consuming little to no cooked food; the raw diet may be fruitarian, vegetarian, or omnivorous.
At least ten thousand years ago, humans developed agriculture, which has substantially altered the kind of food people eat. This has led to increased populations, the development of cities, and, due to increased population density, the wider spread of infectious diseases. The types of food consumed, and the way in which they are prepared, has varied widely by time, location, and culture.
The last century or so has produced enormous improvements in food production, preservation, storage and shipping. Today almost every locale in the world has access to not only its traditional cuisine, but many other world cuisines.
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Brain, mind, and consciousness
Main articles: Human brain, mind, and Consciousness
The human brain.The human brain is the center of the central nervous system in humans, as well as the primary control center for the peripheral nervous system. The brain controls "lower", or involuntary, autonomic activities such as heart rate, respiration, and digestion. The brain also controls "higher" order, conscious activities, such as thought, reasoning, and abstraction.[21] The human brain is generally regarded as more capable of these higher order activities, and more "intelligent" in general, than any other species. While other animals are capable of creating structures and using simple tools—mostly as a result of instinct and learning through mimicry—human technology is vastly more complex, constantly evolving and improving with time. Even the most ancient human tools and structures are far more advanced than any structure or tool created by any other animal.[22]
The human ability to think abstractly may be unparalleled in the animal kingdom. Human beings are one of only six species to pass the mirror test—which tests whether an animal recognizes its reflection as an image of itself—along with chimpanzees, bonobos, orangutans, dolphins and possibly pigeons. Human beings under the age of 2 typically fail this test.[23] However, this may be a matter of degree rather than a sharp divide. Monkeys have been trained to apply abstract rules in tasks.[24]
The 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. Cognitive scientist Daniel Dennett, for example, argues that there is no such thing as a narrative centre called the "mind", but that instead there is simply a collection of sensory inputs and outputs: different kinds of "software" running in parallel.[25]
Humans study the more physical aspects of the mind and brain, and by extension of the nervous system, 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.
Social psychology links sociology with psychology in their shared study of the nature and causes of human social behavior, with an emphasis on how people think towards each other and how they relate to each other. The behavior and mental processes of animals, 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.
2006-08-23 02:12:24
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answer #7
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answered by Linda 7
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