Science & Philosophy: Gastrula to Glow discharge

Science Encyclopedia

Gay Studies - Premodern Traditions Of Same-sex Love In The West, Non-western Traditions, The Medicalized, Industrialized Nation-state

Gay studies in the early twenty-first century is a lively interdisciplinary field encompassing studies of literature, anthropology, sociology, psychology, the visual arts, indeed all fields in which nonheteronormative sexuality—and its institutionalized suppression—has become a point of politico-philosophical argument. It has two origins: a more recent starting point in twentieth-cen…

less than 1 minute read

Gazelles - Territory And Social Arrangements, Mating And Breeding, Preservation And Adaptation

Gazelles are medium-sized fawn-colored antelopes found in arid parts of the world, mainly in Ethiopia, Somalia, northern Africa and around the Sahara Desert, parts of the Middle East, India, and Central Asia. Gazelles are horned animals with a four-chambered stomach and cloven hooves. Gazelles are cud chewers (ruminants), and they lack upper canine and incisor teeth. Gazelles tear grass, foliage, …

less than 1 minute read

Gears

A gear is a toothed disk attached to a rotating rod or shaft that transmits and modifies rotary motion by working in conjunction with another gear. Usually circular in shape, the protrusions of one gear mesh into the profile of its mate to obtain a predetermined mechanical advantage. For example, if one gear wheel has ten times as many teeth as the wheel that drives it, it will make one tenth of a…

2 minute read

Geckos - Distribution And Habitat, Physiology And Reproduction, Defensive Behavior

Geckos are small night-lizards found in the tropics and subtropics, and number more than 650 species in the A parachute gecko (Ptychozoon kuhli). Photograph by Tom McHugh. The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. family Gekkonidae, divided into four subfamilies (the Diplodactylinae, the Gekkoninae, the Sphaerodactylinae, and the Eublepharinae)…

1 minute read

Geese - Geese Of North America, Economic Importance Of Geese, Factors Affecting The Abundance Of Geese, Status

Geese are large birds in the subfamily Anserinae of the waterfowl family Anatidae, consisting of ducks, geese, and swans. Geese occur in many types of aquatic habitats, on all continents but Antarctica. Most geese breed in freshwater marshes, salt marshes, or marsh-fringed, open-water wetlands. Geese typically winter in those sorts of natural habitats and in estuaries, although in some regions the…

1 minute read

Gelatin

Gelatin is an edible protein made from the skin, bones and ligaments of animals. It is clear, usually colorless or pale yellow, odorless and tasteless, and dissolves in water. The hot solution is liquid, but as it cools, it "gels," forming a semi-solid, which is soft and flexible, yet firm enough to hold any shape into which it may be molded or cut. A familiar example of gelatin is t…

2 minute read

Gender in Art - From Antique Through Classical Art, Middle Ages, The Renaissance And The Baroque, Eighteenth And Nineteenth Centuries

Gender, other than a biological or physical determination of the sexes, is a cultural and social classification of masculinity and femininity. Gender presentations in art are the outcome of the cultural process of defining sexual and social identity. Pictorial art and literature, as means of expression through transformation and stylization, are the predominant media reflecting this cultural proce…

1 minute read

Gender in the Middle East - Origins, Anthropology, Literature, And History, Gender Politics: The Veil And The Koran

The term gender has no exact correlate in Middle Eastern sources, but instead is identified by scholars as a major analytical tool in the definition of differences between men and women. Many researchers in every discipline argue that gender has always been embedded in all societies, past and present. Scholars who study gender seek to question dominant, normative definitions of every society…

less than 1 minute read

Gender - Overview - Some Research On Gender Differences, Challenge To Bipolar Assumptions, Gender Studies, Variations In Gender Behavior Between And Among The Sexes

Gender is an old term in linguistic discourse used to designate whether nouns are masculine, feminine, or neuter. It was not normally used in the language of social or natural sciences or in sexology until 1955, when John Money adopted the term to serve as an umbrella concept to distinguish femininity, or womanliness, and masculinity, or manliness, from biological sex (male or female). Though the …

2 minute read

Gender Studies: Anthropology - Kinship And/or Gender?, Rituals Of Becoming: The Making Of Sexual Difference, Feminist Interventions: The Legacy Of The Seventies

Gender studies in anthropology has a relatively short history, dating to the latter half of the twentieth century, but its prehistory can be discerned in the discipline's early concern with kinship and social reproduction. At the turn of the twentieth century, anthropologists focused their attentions mainly on small-scale societies in which kinship appeared to provide the organizing structu…

1 minute read

Gene - History, Gene Expression

A gene is the basic structural unit of inheritance in biological organisms. It is made up of a short segment of DNA and contains the necessary information to produce a specific protein. Each gene is separated from each other by non-coding sequences that serve other functions. Genes are strung together and tightly packed into structures called chromosomes. All the genes in an organism are located o…

1 minute read

Gene Chips and Microarrays

The Human Genome Project began in 1990, with the goal of sequencing the complete human genome. Although estimates to complete the daunting project initially ranged up to forty years, with advances in technolo gy—including gene chip and microarray technology— Gloved hand holding a device for rapidly analyzing samples of DNA at the scene of a crime. Photograph by Sam Ogden. Photo …

2 minute read

Gene Mutation

The term mutation was originally coined by Dutch botanist Hugo De Vries (1848–1935) to describe a new approach to explain evolution, although it is quite different than the current definition. De Vries discovered new forms of the Evening Primrose (Oenothera lamarcklana) that were growing in a meadow. He attributed these new varieties and the method for which new species arise to what he cal…

6 minute read

Gene Splicing - Alternative Splicing, Spliceosomes, Splicing Out Introns, Other Splicing Events, Recombinant Dna Technology, Applications Of Gene Splicing

Genes are DNA sequences that code for protein. Gene splicing is a form of genetic engineering where specific genes or gene sequences are inserted into the genome of a different organism. Gene splicing can also specifically refer to a step during the processing of deoxyribonucleic acid (DNA) to prepare it to be translated into protein. Gene splicing can also be applied to molecular biology techniqu…

2 minute read

Gene Therapy - The Biological Basis Of Gene Therapy, Viral Vectors, The History Of Gene Therapy, Diseases Targeted For Treatment By Gene Therapy

Gene therapy is a rapidly growing field of medicine in which genes are introduced into the body to treat diseases. Gene therapy is the name applied to the treatment of inherited diseases by corrective genetic engineering of the dysfunctional genes. It is part of a broader field called genetic medicine, which involves the screening, diagnosis, prevention and treatment of hereditary conditions in hu…

1 minute read

Generation - Bibliography

In its most widely accepted modern sense, a generation is comprised of a group of people born around the same time and sharing certain formative experiences. The concept of generations has been used by social scientists, historians, and anthropologists to explain social change over time and to identify differences within social groups. The term has also been applied loosely to describe literary gr…

12 minute read

Genetic Engineering

Genetic engineering is the alteration of genetic material with a view to producing new substances or creating new functions. The technique became possible in the 1950s, when scientists discovered the structure of DNA molecules and learned how these molecules store and transmit genetic information. Largely as a result of the pioneering work of James Watson and Francis Crick, scientists were able to…

7 minute read

Genetic Identification of Microorganisms

The advent of molecular technologies and the application of genetic identification in clinical and forensic microbiology have greatly improved the capability of laboratories to detect and specifically identify an organism quickly and accurately. In the wake of the 2001 anthrax attacks utilizing the United States mail, a great deal of investigative attention turned to identification of the source o…

6 minute read

Genetic Testing

The use of genetic information to predict future onset of disease in an asymptomatic (presymptomatic) person is called predictive genetic testing. Every aspect of our being is influenced by both genes and environment. In the future, a strategy for influencing development may be to alter genes. At present, the environment in which genes act can sometimes be changed, and thereby moderate their impac…

4 minute read

Genetically Modified Foods and Organisms

While the term genetically modified organisms has arisen within the past decade, humans have for centuries been using microorganisms to make products like beer and cheese, and plants and animals have been carefully bred to improve the quality and quantity of the food supply. The elucidation of the structure of DNA and the development of the discipline of molecular biology has made possible the acc…

8 minute read

Genetics - The History Of Genetics, The Biology Of Genetics, The Genetic Code, Dominant And Recessive Traits

Genetics is the branch of biology concerned with the science of heredity, or the transfer of specific characteristics from one generation to the next. Genetics focuses primarily on genes, coded units found along the DNA molecules of the chromosomes, housed by the cell nucleus. Together, genes make up the blueprints that determine the entire development of the species of organisms down to specific …

1 minute read

Genets

Genets are mongoose-like mammals in the family Viverridae in the order Carnivora. Other members of this family include civets, linsangs, mongooses and the fossa. The genet genus Genetta has three subgenera and nine species. Genets are found in Africa south of the Sahara desert, in the southwestern Arabian Peninsula, and in southern Europe. Genets have a long body, short legs, a pointed snout, prom…

3 minute read

Genius - Genius In The Twentieth Century, Bibliography

The notion of genius as it is known in the early twenty-first century emerged most fully during the eighteenth-century Enlightenment period. Although the idea of genius was around before the time of Immanuel Kant (1724–1804), Kant most clearly defined it in the late eighteenth century in his third critique, The Critique of Judgment. In fact, Kant's discussion still influences contemp…

2 minute read

Genome

The genome (sometimes spelled geneome) is, in the broadest use of the term, the full set of genes or genetic material carried by a particular organism representing a particular species or population. The size of a genome is usually measured in numbers of genes or base pairs. With the success of the Human Genome Project and other international genome projects and programs, by 2003, scientists have,…

2 minute read

Genomics (Comparative)

The study of an organism's total complement of genetic material, called its genome, has become indispensable for shedding light on its biochemistry, physiology, and patterns of inheritance. Even more can be gained by comparing the genomes of multiple organisms to discern how their DNA sequences have changed over evolutionary time. This technique has become increasingly valuable with the exp…

4 minute read

Genotype and Phenotype

A genotype describes the actual set (complement) of genes carried by an organism. In contrast, phenotype refers to the observable expression of characters and traits coded for by those genes. Although phenotypes are based upon the content of the underlying genes comprising the genotype, the expression of those genes in observable traits (phenotypic expression) is also, to varying degrees, influenc…

4 minute read

Genre - Classical Origins, Renaissance, Neoclassical, And Romantic Conceptions, Twentieth-century Perceptions, The Future Of Genre

Genre is the division and grouping of texts on the basis of formal, thematic, or stylistic criteria. Texts may be produced, it can be argued, in compliance with or against the strictures of an established and identifiable genre, though it is equally feasible to impose a genre identity upon a work in retrospect, thus attributing to it further possibilities of meaning or, conversely, limiting its po…

4 minute read

Geocentric Theory

Rejected by modern science, the geocentric theory (in Greek, ge means earth), which maintained that Earth was the center of the universe, dominated ancient and medieval science. It seemed evident to early astronomers that the rest of the universe moved about a stable, motionless Earth. The Sun, Moon, planets, and stars could be seen moving about Earth along circular paths day after day. It appeare…

5 minute read

Geochemistry - History Of The Science Of Geochemistry, Characteristics And Processes, Geochemistry For The Future

Geochemistry is the science or study of the chemistry of the earth. Geochemists who practice this science are interested in the origin of chemical elements, their evolution, the classes and many divisions of minerals and rocks and how they are created and changed by earth processes, and the circulation of chemical elements through all parts of the earth including the atmosphere and biological form…

1 minute read

Geode

Geodes are hollow rock masses that are lined with crystals that have grown toward the center of the cavity. Geodes are usually roughly spherical in shape, up to 12 A blue geode. © Royalty-Free/Corbis. Reproduced by permission. in (30 cm) or more in diameter. Most frequently, the crystals growing within a geode are quartz, calcite, or fluorite, though occurrences of other minerals are…

2 minute read

Geodesic Dome

A geodesic dome is a spherical building in which the supporting structure is a lattice of interconnecting tetrahedrons (a pyramid with three sides and a base) and octahedrons (an eight sided figure—two pyramids with four sides and a base, placed base to base). The first contemporary geodesic dome on record is Walter Bauersfeld's, who realized the utility of projecting the constellati…

2 minute read

Geographic and Magnetic Poles

Earth's geographic poles are fixed by the axis of Earth's rotation. On maps, the north and south geographic poles are located at the congruence of lines of longitude. Earth's geographic poles and magnetic poles are not located in the same place – in fact they are hundreds of miles apart. As are all points on Earth, the northern magnetic pole is south of the northern geo…

2 minute read

Geologic Map

Geologic maps are graphical representations of rocks, sediments, and other geologic features observed or inferred to exist at or beneath Earth's surface. They can be based on observations of outcrops in the field, interpretation of aerial photographs or satellite images, and information obtained during the drilling of exploratory boreholes. Outcrops can be obscured, particularly in areas co…

2 minute read

Geology

Geology is the study of Earth. Modern geology includes studies in seismology (earthquake studies), volcanology, energy resources exploration and development, tectonics (structural and mountain building studies), hydrology and hydrogeology (water-resources studies), geologic mapping, economic geology (e.g., mining), paleontology (ancient life studies), soil science, historical geology and stratigra…

4 minute read

Geometry - Antiquity And The Middle Ages, Modern Era, Twentieth Century, Bibliography

While the origins of geometry are likely to remain a matter of pure speculation, the elaborate written cultures of ancient Egypt and Babylon provide a wealth of information about the uses of geometry. Area and volume measurements abound in work connected with taxation, the provision of cities, and large-scale building works. Sometimes the Babylonians' evidence (which survives because they w…

less than 1 minute read

Geomicrobiology

Geomicrobiology refers to the activities of microorganisms (usually bacteria) that live beneath the surface of the Earth. The field of study is also referred to as biogeochemistry and subsurface microbiology. Habitats of the organisms include the ocean and deep within the rock that makes up Earth's crust. The study of the identities and activities of such organisms is important from a basic…

6 minute read

Geophysics

Geophysics is the study of Earth's physical character, including the solid planet, the atmosphere, and bodies of water. Geophysical investigations, therefore, often draw upon information and techniques developed in scientific disciplines such as physics, geology, and astronomy. Major areas of modern geophysical research include seismology, volcanology and geothermal studies, tectonics, geom…

3 minute read

Geotropism

Plants can sense the Earth's gravitational field. Geotropism is the term applied to the consequent orientation response of growing plant parts. Roots are positively geotropic, that is, they will bend and grow downwards, towards the center of the Earth. In contrast, shoots are negatively geotropic, that is, they will bend and grow upwards, or away, from the surface. These geotropisms can be …

2 minute read

Gerbils

Gerbils are rat-like rodents in the mammalian family Muridae, which also includes rats, mice, voles and lemmings. Some authorities place the gerbils in a separate family Gerbilidae, together with the pigmy gerbils. Wild gerbils are rat-sized, long-tailed rodents with rather long hind feet. Nearly all live in self-dug burrows and forage at night feeding mostly on seeds. Gerbils are probably derived…

4 minute read

Germ Cells and the Germ Cell Line

Germ cells are one of two fundamental cell types in the human body. Germ cells are responsible for the production of sex cells or gametes (in humans, ovum and spermatozoa). Germ cells also constitute a cell line through which genes are passed from generation to generation. The vast majority of cells in the body are somatic cells. Indeed, the term somatic cell encompasses all of the differentiated …

2 minute read

Germ Theory

The germ theory is a fundamental tenet of medicine that states that microorganisms, which are too small to be seen without the aid of a microscope, can invade the body and cause certain diseases. Until the acceptance of the germ theory, many people believed that disease was punishment for a person's evil behavior. When entire populations fell ill, the disease was often blamed on swamp vapor…

7 minute read

Germination

Germination is the process by which a seed begins its development into a mature plant. Germination begins with an increase of metabolic activity within the seed. The first visible sign of germination in angiosperms (flowering plants) is generally an enlargement of the seed, due to intake of water from the environment. The seed's covering may wrinkle and crack at this time. Soon afterward, t…

1 minute read

Gerontology

Gerontology is a branch of sociology that studies aging among populations internationally, and monitors efforts to deal with problems arising in old age. It differs from geriatrics the same way that psychology is separate from psychiatry. A psychologist's inquiries apply to general questions about how the human brain and mind work. A psychiatrist is more concerned with involving patients in…

2 minute read

Gesnerias

Members of the Gesneria family, the Gesneriaceae, are herbs, shrubs, sometimes trees or woody vines. The Gesneriaceae is a large family composed of approximately 120 genera and 1,800 species. With the exception of two genera (Haberlea and Ramonda), which are native to temperate Europe, they are found only in the tropical and subtropical regions of the world. Although none are native to the United …

2 minute read

Gesture - The Study Of Gestures, Gestures In The Arts, Bibliography

The concept of gesture suffers to some extent from insufficiently defined and imprecisely drawn outlines of what we understand by this term. The Oxford English Dictionary defines gesture as any "significant movement of limb or body"; Merriam Webster's Collegiate Dictionary defines it as "any movement of the body, or part of the body, that expresses or emphasizes an idea…

3 minute read

Geyser

A geyser is an intermittent or semi-regularly periodic spout of geothermally heated groundwater and steam. Any subsurface encounter between water and heat produces a hydrothermal process. The heat is usually supplied by upwellings of magma from the mantle, the water by precipitation that percolates downward through surface rocks. Some oceanic water enters the mantle at subduction zones and becomes…

3 minute read

Ghetto - Jewish Urban Quarters Before The Ghetto, Establishment Of Ghettos, Ghetto As Metaphor For Slum, Black Ghettos

Jewish family in Nazi ghetto, Lublin, Poland, c. 1941. Although the term ghetto has evolved to serve as a name for any poor urban neighborhood, it was originally used in the sixteenth century to denote an area in which Jews were forced to live. AP/WIDE WORLD PHOTOS The name of a district in sixteenth-century Venice where Jews were required to live, ghetto came to be the name for any segrega…

1 minute read

Gibbons and Siamangs - Species of gibbons and siamangs

Gibbons are species of tropical forest apes in the family Pongidae. This family contains all of the anthropoid apes, which are the closest living relatives of humans (Homo sapiens), in terms of their anatomy, physiology, and behavior. Like other anthropoid primates, gibbons lack a tail, they have a more-or-less upright posture, and they have a well-developed brain. However, gibbons are generally r…

7 minute read

The Gift - Bibliography

Reflection on gifts and their paradoxes goes back to the Bible, where humans are reminded that everything they have is a gift from God, for which they must be grateful and which should inspire them to give to others. Yet the Scriptures also condemn gifts, as those to judges, which corrupt or harm. Greek literary texts describe a wide range of gift practices, from the honorable gifts among warriors…

10 minute read

Gila Monster

The Gila monster (Heloderma suspectum) is a large, strikingly-colored venomous lizard. The gila monster and the Mexican beaded lizard (Heloderma horridum) are the only members of the beaded lizard family, Helodermatidae. The Gila monster occurs in rocky, semi-arid habitats from the Colorado River basin in the southwestern United States to the western regions of Mexico and Guatemala. The Gila monst…

2 minute read

Ginger

The ginger family, Zingiberaceae, includes about 50 genera and 1,300 species of plants, a few of which have culinary or medicinal uses. The common ginger (Zingiber officinale) is one of the oldest and most commonly used spices. Ginger for these uses is obtained from the tuberous rhizome, or underground stem of the plant. The common ginger is native to Southeast Asia, where it has been cultivated f…

1 minute read

Ginkgo

The ginkgo, or maidenhair tree (Ginkgo biloba) is an unusual species of gymnosperm, having broad leaves, and seasonally deciduous foliage that turns yellow and is dropped in autumn. The ginkgo is a dioecious plant, which means that male and female functions are performed by separate trees. The ginkgo is famous as a socalled "living fossil," because it is the only surviving member of …

2 minute read

Ginseng

Ginseng refers to several species of plants in the genus Panax, family Araliaceae. Ginseng is a perennial, herbaceous plant, with compound leaves that grow from a starchy root. The natural habitat of ginseng is the understory of mature angiosperm forest in the temperate zones of east Asia and eastern North America. The root of ginseng is highly valued as having many therapeutic properties by pract…

2 minute read

Giraffes and Okapi - Giraffes, The Okapi

Giraffes are a species of large, long-legged, long-necked ungulates in the family Giraffidae, order Artiodactyla. Giraffes are the tallest living animals on Earth. Okapis are a close relative, but these animals do not have such long legs or neck. The giraffe is a widespread animal of grasslands and savannas of sub-Saharan Africa. The okapi is a much rarer animal and occurs in tropical forest. Both…

less than 1 minute read

GIS

GIS is the common abbreviation for geographic information systems, a powerful and widely used computer database and software program that allows scientists to link geographically referenced information related to any number of variables to a map of a geographical area. GIS allows its users to analyze and display data using digitized maps. In addition, GIS can generate maps and tables useful to a w…

2 minute read

Glaciers - How Glaciers Form, Types Of Glaciers, Glaciers' Effects, Clues To The Earth's Past And Future

Glaciers are flowing masses of ice, created by years of snowfall and cold local temperatures. Approximately one tenth of the Earth is covered by glaciers. Glaciers are most numerous near the poles, covering most of Antarctica and Greenland and parts of Iceland, Canada, Russia, and Alaska; they also exist in mountainous regions on every continent except Australia. From the air, a glacier looks dece…

less than 1 minute read

Glands

Glands are aggregates of specialized cells that secrete or excrete chemical substances which are used elsewhere in the body. Glands carry out regulatory, digestive, reproductive, and other functions in the body. A gland may be an independent structure or may be incorporated into another, larger, structure that has still other functions. In addition, a gland can be endocrine, secreting its hormones…

1 minute read

Glass

Early peoples were likely to have discovered natural glass, which is created when lightning strikes sand, and were certain to have used obsidian-a dark volcanic glass-for weapons, ornaments, and money. The first manufactured glass probably took the form either of glass beads or ceramic glaze and appeared around 4000-5000 B.C. Surviving examples of Egyptian and Mesopotamian glass objects date to ar…

4 minute read

Global Climate - Global Climate Patterns, Global Climate Change

The long-term distribution of heat and precipitation on Earth's surface is called global climate. Heat from the sun keeps the Earth's average temperature at about 60°F(16°C), within a range that allows for biological life and maintains the planet's life-sustaining reservoirs of liquid water. Astronomical variations and atmospheric shielding cause incoming solar r…

9 minute read

Global Positioning System

Long before the space age, people used the heavens for navigation. Besides relying on the Sun, Moon, and Stars, the early travelers invented the magnetic compass, the sextant, and the seagoing chronometer. Eventually, radio navigation in which a position could be determined by receiving radio signals broadcast from multiple transmitters, came into existence. Improved high frequency signals gave gr…

3 minute read