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Category:Developmental Biology

Category:Developmental biology

Developmental biology is the study of the process by which organisms grow and develop. Originally termed embryology, today developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy. The related field of evolutionary developmental biology was formed largely in the 1990s and is a synthesis of findings from molecular developmental biology and evolutionary biology which considers the diversity of organismal form in an evolutionary context. developmental biology ko:분류:발생생물학 ja:Category:発生生物学

Cell growth

The term cell growth is used in two different ways in biology. When used in the context of reproduction of living cells the phrase "cell growth" is shorthand for the idea of "growth in cell numbers by means of cell reproduction." During cell reproduction one cell (the "parental" cell) divides to produce daughter cells. In other contexts, "cell growth" refers to increases in cell size.

Cell size

Many cells never have a large increase in size after they are first formed from a parental cell. Typical stem cells reproduce, double in size, then reproduce again. Most Cytosolic contents such as the endomembrane system and the cytoplasm easily scale to larger sizes in larger cells. If a cell becomes too large, the normal cellular amount of DNA may not be adequate to keep the cell supplied with RNA. Large cells often replicate their chromosomes to an abnormally high copy number or become multinucleated. Large cells that are primarily for nutrient storage can have a smooth surface membrane, but metabolically active large cells often have some sort of folding of the cell surface membrane in order to increase the surface area available for transport functions.

Yeast cell size regulation

The relationship between cell size and cell division has been extensively studied in yeast. For some cells, there is a mechanism by which cell division is not initiated until a cell has reached a certain size. If the nutrient supply is restricted (after time t = 2 in the diagram, below) and the rate of increase in cell size is slowed, the time period between cell divisions is increased. Yeast cell size mutants were isolated that begin cell division before reaching the normal size (wee mutants). The Wee1 protein is a tyrosine kinase. It normally phosphorylates the Cdc2 cell cycle regulatory protein on a tyrosine residue. This covalent modification of the molecular structure of Cdc2 inhibits the enzymatic activity of Cdc2 and prevents cell division. In Wee1 mutants, there is less Wee1 activity and Cdc2 becomes active in smaller cells, causing cell division before the yeast cells reach their normal size. Cell division may be regulated in part by dilution of Wee1 protein in cells as they grow larger. Cell cycle and growth

Cell size regulation in mammals

The protein mTOR is a serine/threonine kinase that regulates translation and cell division. Nutrient availability influences mTOR so that when cells are not able to grow to normal size they will not undergo cell division. The details of the molecular mechanisms of mammalian cell size control are currently being investigated. The size of post-mitotic neurons depends on the size of the cell body, axon and dendrites. In vertebrates, neuron size is often a reflection of the number of synaptic contacts onto the neuron or from a neuron onto other cells. For example, the size of motoneurons usually reflects the size of the motor unit that is controlled by the motoneuron. Invertebrates often have giant neurons and axons that provide special functions such as rapid action potential propagation. Mammals also use this trick for increasing the speed of signals in the nervous system, but they can also use myelin to accomplish this, so most human neurons are releatively small.

Other experimental systems for the study of cell size regulation

One common means to produce very large cells is by cell fusion to form syncytia. For example, very long (several inches) skeletal muscle cells are formed by fusion of thousands of myocytes. Genetic studies of the fruit fly Drosophila have revealed several genes that are required for the formation of multinucleated muscle cells by fusion of myocyes. Some of the key proteins are important for cell adhesion between myocytes and some are involved in adhesion-dependent cell-to-cell signaling that allows for a cascade of cell fusion events. Oocytes can be unusually large cells in species for which embryonic development takes place away from the mother's body. Their large size can be achieved either by pumping in cytosolic components from adjacent cells through cytoplasmic bridges (Drosophila) or by internalization of nutrient storage granules (yolk granules) by endocytosis (frogs). Increases in the size of plant cells is complicated by the fact that almost all plant cells are inside of a solid cell wall. Under the influence of certain plant hormones the cell wall can be remodeled, allowing for increases in cell size that are important for the growth of some plant tissues. Most unicellular organisms are microscopic in size, but there are some giant bacteria and protozoa that are visible to the naked eye. See: [http://wikibooks.org/wiki/Biology_Cell_biology_Introduction_Cell_size Table of cell sizes] - [http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10205058 Dense populations of a giant sulfur bacterium in Namibian shelf sediments] - [http://www.bms.ed.ac.uk/research/others/smaciver/chaos.htm Large protists of the genus Chaos, closely related to the genus Amoeba]

Cell reproduction

The process of cell reproduction has three major parts. The first part of cell reproduction involves the replication of the parental cell's DNA. The second major issue is the separation of the duplicated DNA into two equally sized groups of chromosomess. The third major aspect of cell reproduction is the physical division of entire cells, usually called cytokinesis. Cell reproduction is more complex in eukaryotes than in other organisms. Non-eukaryotic cells such as bacterial cells reproduce by binary fission, a process that includes DNA replication, chromosome segregation, and cytokinesis. Eukaryotic cell reproduction either involves mitosis or a more complex process called meiosis. Mitosis and meiosis are sometimes called the two "nuclear division" processes. Binary fission is similar to eukaryotic cell reproduction that involves mitosis. Both lead to the production of two daughter cells with the same number of chromosomes as the parental cell. Meiosis is used for a special cell reproduction process of diploid organisms. It produces four special daughter cells (gametes) which have half the normal cellular amount of DNA. A male and a female gamete can then combine to produce a zygote, a cell which again has the normal amount of chromosomes. For details see the individual articles on DNA replication, binary fission, mitosis, meiosis, and cytokinesis. The rest of this article is a comparison of the main features of the three types of cell reproduction that either involve binary fission, mitosis, or meiosis. The diagram below depicts the similarities and differences of these three types of cell reproduction. cytokinesis

Comparison of the three types of cell reproduction

The DNA content of a cell is duplicated at the start of the cell reproduction process. Prior to DNA replication, the DNA content of a cell can be represented as the amount Z (the cell has Z chromosomes). After the DNA replication process, the amount of DNA in the cell is 2Z (multiplication: 2 x Z = 2Z). During Binary fission and mitosis the duplicated DNA content of the reproducing parental cell is separated into two equal halves that are destined to end up in the two daughter cells. The final part of the cell reproduction process is cell division, when daughter cells physically split apart from a parental cell. During meiosis, there are two cell division steps that together produce the four daughter cells. After the completion of binary fission or cell reproduction involving mitosis, each daughter cell has the same amount of DNA (Z) as what the parental cell had before it replicated its DNA. These two types of cell reproduction produced two daughter cells that have the same number of chromosomes as the parental cell. After meiotic cell reproduction the four daughter cells have half the number of chromosomes that the parental cell originally had. This is the haploid amount of DNA, often symbolized as N. Meiosis is used by diploid organisms to produce haploid gametes. In a diploid organism such as the human organism, most cells of the body have the haploid amount of DNA, 2N. Using this notation for counting chromosomes we say that human somatic cells have 46 chromosomes (2N = 46) while human sperm and eggs have 23 chromosomes (N = 23). Humans have 23 distinct types of chromosomes, the 22 autosomes and the special category of sex chromosomes. There are two distinct sex chromosomes, the X chromosome and the Y chromosome. A diploid human cell has 23 chromosomes from that person's father and 23 from the mother. That is, your body has two copies of human chromosome number 2, one from each of your parents.

Chromosomes

Immediately after DNA replication a human cell will have 46 "double chromosomes". In each double chromosome there are two copies of that chromosome's DNA molecule. During mitosis the double chromosomes are split to produce 92 "single chromosomes", half of which go into each daughter cell. During meiosis, there are two chromosome separation steps which assure that each of the four daughter cells gets one copy of each of the 23 types of chromosome (see meiosis for details).

Why we have sex

Main article: Evolution of sex If the type of cell reproduction that uses mitosis can reproduce our cells, why do we bother with the more complicated process of meiosis? You may think you know why you have sex, but you probably do not know the real reason; the reason why meiosis confers a selective advantage. Notice that when meiosis starts, the two copies of chromosome number 2 are adjacent to each other. During this time, there can be genetic recombination events. Parts of the chromosome 2 DNA that you got from your mother (red) will swap over to the chromosome 2 DNA molecule that you got from your father (green). Notice that in mitosis the two copies of chromosome number 2 do not interact. It is these new combinations of parts of chromosomes that provide the major advantage for sexually reproducing organisms by allowing for new combinations of genes and more efficient evolution. However, in organisms with more than one set of chromosomes at the main life cycle stage, sex may also provide an advantage because, under random mating, it produces homozygotes and heterozygotes according to the Hardy-Weinberg ratio.

Morphogenesis

Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. Morphogenesis is concerned with the shapes of tissues, organs and entire organisms and the positions of the various specialized cell types. Cell growth and differentiation can take place in cell culture or inside of tumor cell masses without the normal morphogenesis that is seen in an intact organism. The study of morphogenesis involves an attempt to understand the processes that control the organized spatial distribution of cells that arises during the embryonic development of an organism and which give rise to the characteristic forms of tissues, organs and overall body anatomy. In the human embryo, the change from a cluster of nearly identical cells at the blastula stage to a post-gastrulation embryo with structured tissues and organs is controlled by the genetic "program" and can be modified by environmental factors. Some of the earliest ideas on how physical and mathematical processes and constraints affect biological growth were written by D'Arcy Wentworth Thompson and Alan Turing. These works postulated the presence of chemical signals and physico-chemical processes such as diffusion, activation and deactivation in cellular and organismic growth. The fuller understanding of the mechanisms involved in actual organisms required the discovery of DNA and the development of molecular biology and biochemistry. Several types of molecules are particularly important during morphogenesis. Morphogens are soluble molecules that can diffuse and carry signals that control cell differentiation decisions in a concentration-dependent fashion. Morphogens typically act through binding to specific protein receptors. An important class of molecules involved in morphogenesis are transcription factor proteins that determine the fate of cells by interacting with DNA. These can be coded for by master regulatory genes and either activate or deactivate the transcription of other genes and, in turn, these secondary gene products can regulate the expression of still other genes in a regulatory cascade. Another class of molecules involved in morphogenesis are molecules that control cell adhesion. For example, during gastrulation clumps of stem cells switch off their cell-to-cell adhesion, become migratory, and take up new positions with an embryo where they again activate specific cell adhesion proteins and form new tissues and organs. Several examples that illustrate the roles of morphogens, transcription factors and cell adhesion molecules in morphogenesis are discussed below.

Anterior-posterior axis patterning in Drosophila

Morphogenesis of the fruit fly Drosophila melanogaster starts with the construction of asymmetries within the oocyte and proceeds to pattern formation along the embryonic axes. The development of Drosophila is particularly well studied, and it is representative of one major class of insects. Other multicellular organisms sometimes use similar mechanisms for axis formation, although the relative importance of signal transfer between the earliest cells of many developing organisms is greater than in the example described here.

Maternal effect genes

oocyte A Drosophila oocyte is a polarized cell. The future anterior-posterior axis of the fly is established by mRNA molecules that are differentially localized within the oocyte. The genes that code for these differentially localized oocyte mRNAs are called maternal effect genes. They have profound effects on the development of a fertilized egg, but they are expressed by cells within the maternal ovary. Bicoid and hunchback are the maternal effect genes that are most important for patterning of anterior parts (head and thorax) of the Drosophila embryo. Nanos and Caudal are maternal effect genes that are important in the formation of more posterior abdominal segments of the Drosophila embryo. Cytoskeletal elements such as microtubules are polarized within the oocyte and can be used to allow the localization of mRNA molecules to specific parts of the cell. Maternally synthesized bicoid mRNAs attach to microtubules and are concentrated at the anterior ends of forming Drosophila eggs. Nanos mRNAs also attach to the egg cytoskeleton but they concentrate at the posterior ends of the eggs. Hunchback and caudal mRNAs lack special location control systems and are fairly evenly spread throughout the interior of egg cells. microtubule When the mRNAs from the maternal effect genes are translated into proteins a Bicoid protein gradient forms at the anterior end of the egg. Nanos protein forms a gradient at the posterior end. The Bicoid protein blocks translation of caudal mRNA so Caudal protein is made only in the posterior part the cell. Nanos protein binds to the hunchback mRNA and blocks its translation in the posterior end of Drosophila embryos. The Bicoid, Hunchback, and Caudal proteins are transcription factors. Bicoid has a DNA-binding homeodomain that binds both DNA and the nanos mRNA. Bicoid binds a specific RNA sequence in the 3' untranslated region of caudal mRNA and blocks translation. Hunchback protein levels in the early embryo are significantly augmented by new hunchback gene transcription and translation of the resulting zygotically produced mRNA. During early Drosophila embryogenesis there are nuclear divisions without cell division. The many nuclei that are produced distribute themselves around the periphery of the cell cytoplasm. Gene expression in these nuclei is regulated by the Bicoid, Hunchback, and Caudal proteins. For example, Bicoid acts as a transcriptional activator of hunchback gene transcription. zygotically zygotically

Gap genes

The other important function of the gradients of Bicoid, Hunchback, and Caudal proteins is in the transcriptional regulation of other zygotically expressed proteins. Many of these are the protein products derived from members of the "gap" family of developmental control genes. Hunchback, krüppel, giant, tailless and knirps are all gap genes. Their expression patterns in the early embryo are determined by the maternal effect gene products and shown in the diagrams on the left side of this page. The gap genes are part of a larger family called the segmentation genes. These genes establish the segmented body plan of the embryo along the anterior-posterior axis. The segmentation genes specify 14 "parasegments" that are closely related to the final anatomical segments. The gap genes are the first layer of a hierarchical cascade of the segmentation control genes. Proteins such as Bicoid can be described as morphogens that act within the syncytial blastoderm of the early Drosophila embryo. These intracellular morphogens enter the nuclei and act as transcription factors to control expression of the gap genes. In the blastoderm stage of Drosophila morphogenesis four types of nuclear specification can be distinguished:
- Anterior (head and thorax)
- Posterior (abdomen)
- Dorso-ventral
- Terminal (special structures at the unsegmented ends of the embryo)

Additional segmentation genes

ventral Two additional classes of segmentation genes are expressed after the gap gene products. The pair-rule genes are expressed in striped patterns of seven bands perpendicular to the anterior-posterior axis (see the example, even-skipped). These patterns of expression are established within the syncytial blastoderm. After these initial patterning events, cell membranes form around the nuclei of the syncytial blastoderm converting it to a cellular blastoderm. ventral The expression patterns of the final class of segmentation genes, the segment polarity genes, are then fine-tuned by interactions between the cells of adjacent parasegments (see the example, engrailed, to the right). The Engrailed protein is a transcription factor (yellow in figure to left) that is expressed in one row of cells at the edge of each parasegment. This expression pattern is initiated by the pair-rule genes (like even-skipped) that code for transcription factors that regulate the engrailed gene's transcription in the syncytial blastoderm. Cells that make Engrailed can make the cell-to-cell signaling protein Hedgehog (green in the figure to the left). Hedgehog is not free to move very far and activates a thin stripe of cells adjacent to the Engrailed-expressing cells. Only cells to one side of the Engrailed-expressing cells are competent to respond to Hedgehog because they express the receptor protein Patched (blue in figure to left). Cells with activated Patch receptor make the Wingless protein (red in the figure). Wingless protein acts as an extracelluar morphogen and patterns the adjacent rows of cells by activated its cell surface receptor, Frizzled in a concentration-dependent fashion. Wingless also acts on Engrailed-expressing cells to stabilize Engrailed expression after the cellular blastoderm forms. The reciprocal signaling by Hedgehog and Wingless stabilizes the boundary between each segment. The Wingless protein is called "wingless" because of the phenotype of some wingless mutants. Wingless also functioned during metamorphosis to coordinate wing formation. The transcription factors that are coded for by segmentation genes regulate yet another family of developmental control genes, the homeotic selector genes. These genes exist in two ordered groups on Drosophila chromosome 3. The order of the genes on the chromosome reflects the order that they are expressed along the anterior-posterior axis of the developing embryo. The Antennapedia group of homeotic selector genes includes labial, antennapedia, sex combs reduced, deformed, and proboscipedia. Labial and Deformed proteins are expressed in head segments where they activate the genes that define head features. Sex-combs-reduced and Antennapedia specify the properties of thoracic segments. The bithorax group of homeotic selector genes control the specializations of the third thoracic segment and the abdominal segments. In 1995, the Nobel Prize for Physiology or Medicine was awarded for studies concerning the genetic control of early embryonic development to Christiane Nüsslein-Volhard, Edward B. Lewis and Eric Wieschaus. Their researches on genetic screening for embryo patterning mutants revealed the role played in early embryologic development by Hox genes like bicoid. An example of a homeotic mutation is the so-called antennapedia mutation. In Drosophila, antennae and legs are created by the same basic "program", they only differ in a single transcription factor. If this transcription factor is damaged, the fly grows legs on its head instead of antennae. See images of this "antennapedia" mutant and others, at [http://flybase.bio.indiana.edu FlyBase]. The term morphogenesis can also be used to describe the development of unicellular life forms that do not have an embryonic stage in their life cycle, or to refer to the evolution of a body structure within a taxonomic group. Morphogenetic responses may be induced in organisms by hormones, or by environmental chemicals ranging from substances produced by other organisms to toxic chemicals or radionuclides released as pollutants.

Biological tissue

Biological tissue is a substance made up of cells that perform a similar function. The study of tissues is known as histology, or, in connection with disease, histopathology. The classical tools for studying the tissues are the wax block, the tissue stain, and the optical microscope, though developments in electron microscopy, immunofluorescence, and frozen sections have all added to the sum of knowledge in the last couple of decades. With these tools, the classical appearances of the tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

Animal Tissues

There are four basic types of tissue in the body of all animals, including the human body and lowar multicellular organisms such as insects. These compose all the organs, structures and other contents.
- Epithelium - Tissues composed of layers of cells that cover organ surfaces such as surface of the skin and inner lining of digestive tract. The tissues serve for protection, secretion, and absorption.
- Connective tissue - As the name suggests, connective tissue holds everything together. Blood is considered a connective tissue.
- Muscle tissue - Muscle cells contain contractile filaments that move past each other and change the size of the cell.
- Nervous tissue - Cells forming the brain, spinal cord and peripheral nervous system.

Plant Tissues

Examples of tissue in other multicellular organisms are vascular tissue in plants, such as xylem and phloem. Plant tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and the vascular tissue.
- Epidermis - Cells forming the outer surface of the leaves and of the young plant body.
- Vascular tissue - The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally.
- Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients.

References

- Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (1986). Biology of Plants (4th ed.). New York: Worth Publishers. ISBN 0-87901-315-X. Category:Anatomy Category:Tissues ms:Tisu biologi ja:組織 (生物学) simple:Tissue (biological)

Anatomy

Anatomy (from the Greek anatomia, from anatemnein, to cut up, cut open), is the branch of biology that deals with the structure and organization of living things. It can be divided into animal anatomy (zootomy) and plant anatomy (phytonomy). Major branches of anatomy include comparative anatomy, histology, and human anatomy. Animal anatomy may include the study of the structure of different animals, when it is called comparative anatomy or animal morphology, or it may be limited to one animal only, in which case it is spoken of as special anatomy. From a utilitarian point of view the study of humans is the most important division of special anatomy, and this human anatomy may be approached from different points of view. From that of Medicine it consists of a knowledge of the exact form, position, size and relationship of the various structures of the healthy human body, and to this study the term descriptive or topographical human anatomy is given, though it is often, less happily, spoken of as anthropotomy. So intricate is the human body that only a small number of professional human anatomists, after years of patient observation, are complete masters of all its details; most of them specialize on certain parts, such as the brain or viscera, contenting themselves with a good working knowledge of the rest. Topographical anatomy must be learned by repeated dissection and inspection of dead human bodies. It is no more a science than a pilot's knowledge is, and, like that knowledge, must be exact and available in moments of emergency. From the morphological point of view, however, human anatomy is a scientific and fascinating study, having for its object the discovery of the causes which have brought about the existing structure of humans, and needing a knowledge of the allied sciences of embryology or developmental biology, phylogeny, and histology. Pathological anatomy (or morbid anatomy) is the study of diseased organs, while sections of normal anatomy, applied to various purposes, receive special names such as medical, surgical, gynaecological, artistic and superficial anatomy. The comparison of the anatomy of different races of humans is part of the science of physical anthropology or anthropological anatomy. In the present edition of this work the subject of anatomy is treated systematically rather than topographically. Each anatomical article contains first a description of the structures of an organ or system (such as nerves, arteries, heart, and so forth), as it is found in humans; this is followed by an account of the development (embryology) and comparative anatomy (morphology), as far as vertebrate animals are concerned; but only those parts of the lower animals which are of interest in explaining human body structure are here dealt with. The articles have a twofold purpose; first, to give enough details of structure to make the articles on physiology, surgery, medicine and pathology intelligible; and, secondly, to give the non-expert inquirer, or the worker in some other branch of science, the chief theories on which the modern scientific groundwork of anatomy is built.
- Major body systems:
- Integumentary system
- Muscular system
- Nervous system
- Reproductive system
- Respiratory system
- Excretory system
- Circulatory system
- Lymphatic system
- Skeletal system (Human skeleton)
- Endocrine system
- Digestive system
- Immune system
- Organs:
- Anus
- Appendix
- Brain
- Breast
- Colon or large intestine
- Diaphragm
- Ear
- Eye
- Heart
- Kidney
- Labia
- Larynx
- Liver
- Lung
- Nose
- Ovary
- Pharynx
- Pancreas
- Penis
- Placenta
- Rectum
- Skin
- Small intestine
- Spleen
- Stomach
- Tongue
- Uterus
- Bones in the human skeleton:
- Collar bone (clavicle)
- Thigh bone (femur)
- Humerus
- Mandible
- Patella
- Radius
- Skull
- Tibia
- Ulna
- Rib
- Vertebrae
- Pelvis
- Sternum
- Glands:
- Ductless gland
- Mammary gland
- Salivary gland
- Thyroid gland
- Parathyroid gland
- Adrenal gland
- Pituitary gland
- Pineal gland
- Tissues:
- Connective tissue
- Endothelial tissue
- Epithelial tissue
- Glandular tissue
- Lymphoid tissue
- Externally visible parts of the human body:
- Abdomen
- Arm
- Back
- Buttock
- Chest
- Ear
- Eye
- Face
- Genitals
- Head
- Joint
- Leg
- Mouth
- Neck
- Scalp
- Skin
- Teeth
- Tongue
- Other anatomic terms (not classified):
- Artery
- Coelom
- Diaphragm
- Gastrointestinal tract
- Hair
- Exoskeleton
- Lip
- Nerve
- Peritoneum
- Serous membrane
- Skeleton
- Skull
- Spinal cord
- Vein

External links

- [http://brainmaps.org High-Resolution Cytoarchitectural Primate Brain Atlases]
- [http://www.innerbody.com/htm/body.html Free online anatomy atlas]
- [http://www.npac.syr.edu/projects/vishuman/VisibleHuman.html The NPAC Visible Human Viewer]
- [http://cancerweb.ncl.ac.uk/omd/index.html On-Line Medical Dictionary]
- [http://www.bartleby.com/107/ Anatomy of the Human Body by Henry Gray]
- [http://www.rtstudents.com/ Online Radiology Anatomy Resources]
- [http://www.wikimd.org/index.php?title=Gray%27s_Anatomy Gray's Anatomy wiki]
- http://immunity-info.net Category:Anatomy ko:해부학 ja:解剖学 simple:Anatomy th:กายวิภาคศาสตร์

1990s

The 1990s refers to the years 1990 to 1999; the last decade of the 20th Century. The 90s were marked with rapid progression of globalization and global capitalism following the collapse of the Soviet Union and the end of the Cold War. Key forces shaping the decade were the Gulf War; popularization of Personal Computer and Internet leading to the dot.com boom.

Events and trends

While optimism and hopes were high following the collapse of Communism, the backlash of the Cold War's effect was only beginning, precipitating the continuation of terrorism in Third World regions that were once the frontlines for American and Soviet foreign politics, particularly in Asia. However, during the 1990s many First World economies such as the United States, Canada, Ireland, Australia, and South Korea experienced steady economic growth for nearly the entire decade. The United Kingdom, after the recession of 1991-92 and Black Wednesday, experienced a run of 51 consecutive quarters of economic growth that stretched into the new millenium. Even less affluent nations such as Malaysia saw tremendous improvements in economic prosperity and quality of life during the 1990s. Many countries, institutions, companies, and organizations also viewed the 90s decade as "a prosperous time", meaning that almost all of them rebounded after many years of failure. Some examples include Apple Computer's revival of power after being at the edge of bankruptcy, breakthroughs in many fields of technology that includes the Internet, virtual reality. Oil and Gas was discovered in many countries and Pope John Paul II's papacy reached its peak. Nevertheless, the 1990s brought tragic conflicts as well, like the Balkan Wars, the Rwandan genocide, the Battle of Mogadishu in Somalia and the first Gulf War.

Criticism/Backlash of the Decade

Despite denials from various sociologists and media pundits, some feel that the 90s were an era of increasing materialism and growing hypocrisy continued from the 1980s. In general it could still be said that the mindset of the 1980s and 1990s were more or less the same. The 1990s are also widely critized for their controversial pop culture obsessed with gore, sex, violence, and language, along with the 2000s to a somewhat lesser extent. The 1990s nonetheless have a very positive receiving into the 2000s and are still considered quite "modern" even as of 2006, with many genres of media from the decade still being quite cool among youth during the 2000s as no great revolutions in pop culture have occurred for some time and only moderate backlash of the decade itself has yet occurred. Also, while not a criticism of the decade per se, some people see the 1990s as the beginning of the 21st Century rather than the end of the 20th Century in an abstract sense based on the fact that the Cold War, a definitive phoenomenon of the 20th Century, was over by about 1991 and the tech boom began to take off a couple years after, and very 21st Century events such as the rise of the Internet and other information technologies and the expansion of Islamic terrorism began to become prominent in the 1990s.

Technology

Internet]
- The Pentium processor is developed by Intel.
- Microsoft introduces Windows 95 to the market, which gained immediate popularity.
- Explosive growth of the Internet, decrease in the cost of computers and other technology.
- Advancements with computer modems, ISDN, cable modems and DSL lead to faster connection to the Internet.
- The development of web browsers such as Netscape and Internet Explorer makes surfing the World Wide Web easier and more user friendly.
- The Java programming language is developed by Sun Microsystems.
- Businesses begin E-commerce websites; companies such as Amazon.com, eBay, AOL, and Yahoo! grew rapidly on the Internet.
- Cell phones burst in popularity and decrease in size, becoming a necessity for modern life.
- Pagers and PDAs become popular communication tools.
- E-mail becomes popular; as a result Microsoft acquires the popular Hotmail.com.
- Year 2000 problem (commonly known as Y2K).
- Microsoft Windows operating system becomes virtually ubiquitous on IBM PCs.
- Development of free operating system Linux is started.
- Breakthrough of compact disc technology, introduced in the 1980s, later branching into DVD.

Science

DVD]
- Detection of extrasolar planets orbiting stars other than the sun.
- The cloning of Dolly the sheep is achieved.
- Human Genome Project begun.
- DNA identification of individuals finds wide application in criminal law.
- Hubble Space Telescope launched in 1990; revolutionizes astronomy.
- Protease inhibitors introduced allowing HAART therapy against HIV; drastically reduces AIDS mortality.
- NASA's spacecraft Pathfinder lands on Mars and deploys a small roving vehicle, Sojourner, that analyzes the planet's geology and atmosphere.
- The Hale-Bopp comet swings past the sun for the first time in 4,200 years.
- Development of biodegradable products, replacing products made from styrofoam; advanced methods for recycling of waste products (such as paper, glass, aluminum) are developed.
- Genetically engineered crops are developed for commercial use.
- Discovery of dark matter, dark energy, and brown dwarves, and first confirmation of black holes.
- The Galileo probe orbits Jupiter, studying the planet and its moons extensively.

War, peace, and politics

Jupiter] Jupiter]
- Reunification of Germany on October 3 1990.
- End of apartheid in South Africa (1990) and election of ANC government of Nelson Mandela.
- Gulf War (resulting from Iraq's invasion of Kuwait) and United Nations embargo on Iraq in 1991.
- North Yemen and South Yemen merge to form Yemen (1991).
- Break up of the Soviet Union in 1991 - the end of the Cold War, United States as sole world superpower.
- The bombing of the World Trade Center in 1993 by an explosive-filled van leads to awareness of international terrorism as a rising threat.
- Eritrea gains independence from Ethiopia (1993).
- European Union is declared in 1992.
- Military actions in Somalia in 1993 lead to questions of the United States' role as a policing officer of the world. (see also, Black Hawk Down).
- Rwandan genocide kills one million people, in 1994.
- The birth of the "Second Republic" in Italy, with the Mani Pulite investigations of 1994.
- Peace process begins in Northern Ireland in 1995
- Balkan war in former Yugoslavia in 1995.
- A decade of women presidents in the Republic of Ireland.
- The United Kingdom hands sovereignty of Hong Kong to the People's Republic of China on July 1, 1997.
- U.S. Congressman Newt Gingrich crafts his manifesto "Contract with America", leading his Republican Party to become the controlling majority in the U.S. House of Representatives.
- U.S. president Bill Clinton's sex scandal with Monica Lewinsky and his impeachment trial in 1998, which lasts the entire year.
- Anti-globalization protests.
- The Second Congo War start in 1998 in central Africa and includes 5 different cultures and 7 different nations. It goes on until 2002.
- In May 1999, Pakistan sends troops covertly to occupy strategic peaks in Kashmir. A month later the Kargil War with India results in a political fiasco for Nawaz Sharif, followed by a military withdrawal to the Line of Control. The incident leads to a military coup in October in which the Prime Minister Nawaz Sharif is ousted by Army Chief Pervez Musharraf.
- Portugal hands sovereignty of Macau to the People's Republic of China on December 20, 1999.

Economics

- Development of GATT, the World Trade Organization and other global economic institutions.
- The North American Free Trade Agreement (NAFTA), which phases out trade barriers between the United States, Mexico and Canada is signed into law by U.S. President Bill Clinton.
- After 1992 the booming of the US stock market, in reference to which Alan Greenspan coined the memorable phrase "irrational exuberance", which eventually stretched into the dot-com boom / dot-com bubble.
- Financial crisis hits East and Southeast Asia in 1997 and 1998 after a long period of phenomenal economic development. See East Asian Tigers.

Culture

Trends/Various

- The Gay 1990s The 1990s saw an increase in gay visibility. Tv shows like thirtysomething,My So called Life and Ellen featured gay characters, Movies like The Birdcage,In and Out and Kiss Me Guido saw mainstream sucess, and celebrities like K.D Lang and George Michael coming out of the closet. Even President Bill Clinton generally held a pro gay rights viewpoint.
- Douglas Coupland publishes the novel Generation X: Tales for an Accelerated Culture, popularizing the term Generation X as the name of the generation born in the late 1960s and early 1970s (then college-age).
- Reality television explodes on MTV with the popularity of The Real World (1992-); along with Road Rules (1995-), Real World/Road Rules Challenge (1998), and Real World reunions, these shows remained popular throughout the 1990s.
- Video games become more advanced, but still a far cry from the systems of the 2000s. The more influential game systems of the Nineties include the Super Nintendo Entertainment System, the Sony Playstation, and the Sega Dreamcast.
- Extreme sports reached a new height in popularity, and by 1995, were given their own annual tournament on US cable network ESPN, the X-Games.
- Black becomes a dominant color in fashion, among several dark colors (see Goth, The Matrix, and Regis Philbin).
- Dogma 95 becomes the leading European artistic film movement by the end of the decade.
- Professional wrestling became extremely popular. After scandals and near bankruptcy due to competition from World Championship Wrestling (WCW), the World Wrestling Federation was repackaged more edgier and realistic. Superstars such as Stone Cold Steve Austin, The Rock, Mick Foley, Steve Borden (Sting), Bill Goldberg, Raven, Sabu and others became household names. At the same time, Extreme Championship Wrestling (ECW) led wrestling's entry into edgier angles.
- Recreational sports such as rock climbing, mountain biking, sky diving, snowboarding, mountain climbing, bungee jumping, in-line skating, kayaking and rowing become hugely popular.
- Extended alcohol sales are implemented to reduce alcohol abuse.
- The 1990s remains a somewhat "cool" decade into the 2000s as many aspects of the 90s continue to be important into the next decade, see New Nineties.

Music

- Grunge music, popularized by Nirvana, big from the fall of 1991 through 1994 but influential to rock up to 2005 (see Post-Grunge), Grunge movement followed by the Britpop movement of about 1995 to 1997 which was in turn followed by numetal.
- Teen pop held over from the late 1980s popular into 1990, returns with Backstreet Boys and Spice Girls in latter third of the decade
- Radiohead comes to be one of the most critically and commercially loved bands since The Beatles. Two of their albums, The Bends and Ok Computer top lists at the end of the decade.
- Rap music gains widespread mainstream acceptance throughout the decade, starting with the success of MC Hammer, Public Enemy and Vanilla Ice around 1989-91 and ending with hip-hop inspired by Puff Daddy, Dr. Dre and Eminem c. 1997-99. By 1999 hip hop had definitely passed rock and roll in popularity.
- Music festivals such as Lollapalooza became popular; a fusing of genres from alternative rock, rap, punk rock and garage bands.
- Rock music begins to be referred to as "alternative" as it is originated in 1980s underground rock and 1970s punk and begins to lose popularity to hip hop.
- Trance, techno and electronica music becomes widely popular at rave parties in Europe/USA and in pop culture, particularly later in the decade. The drug Ecstasy, (aka MDMA or 'X') is popularized by rave culture.
- 1980s backlash, beginning in about 1991 and lasting into the 2000s. During most of the 1990s anything "Eighties" was considered to be ultimately uncool.
- Music becomes more profane, by end of decade a Parental Advisory sticker becomes acceptable rather than controversial.
- In America, country music becomes more mainstream with popular chart topping artist such as Garth Brooks, Shania Twain, LeAnn Rimes, Faith Hill, and Tim McGraw. The trend decreases somewhat in the 2000s.

Television

- Japanimation becomes popular in the United States in the late 1990s with shows Pokemon, Dragonball Z, and Cowboy Bebop.
- Mighty Morphin' Power Rangers gains popularity with kids in the mid 90s; leading to entire Power Rangers series. Barney and Teenage Mutant Ninja Turtles also popular
- MTV moves away from music videos and into original television shows such as The Real World, which is cited as the inspiration for the Reality TV boom of the 2000s.
- Cartoons aimed at an adult audience become popular. Among the most successful are The Simpsons (1989-), Ren & Stimpy (1991-1995), Beavis and Butt-head (1993-1997), South Park (1997-), King of the Hill (1997-), and Family Guy (1999-2002, 2005-).
- Television networks increase programs aimed at twenty- and thirty-somethings. Some of the popular are Beverly Hills 90210 (1990-2000), Melrose Place (1992-1999), Party of Five (1994-2000), Ally McBeal (1997-2002), Friends (1994-2004), and Seinfeld (1989-1998).
- Notable television sitcoms aimed at the teen/preteen market include Boy Meets World (1993-2000), Full House (1987-1995), Family Matters (1989-1998), and Third Rock From The Sun (1996-2001), among many others.
- Major 1990s slang words/phrases, mostly related to hip hop include "homie", "phat", "da bomb", "Audi 5000", "tight", "word to your mother", "Talk to the hand", "You go girl!", and "Wasssuppp!"

Other significant events

Talk to the hand]
- The massive global human impact on the environment, which first garnered attention in the 60s, was widely acknowledged.
- Divorce and scandal rocked the British Royal House of Windsor.
- The assassination of Selena Quintanilla.
- Sex and violence in the media increase, especially in the late part of the decade. Profanity in music reaches peak in the late 90s.
- O.J. Simpson's trial, described in the media as the "trial of the century".
- You go, girl! becomes a popular phrase in the media as feminism is more widely accepted and publicised in the media with The Spice Girls, the WNBA, women's boxing, Sex and the City and others showcasing modern femininity.
- The Vieques controversy.
- The Oklahoma City Bombing, the bombing of a federal building in Oklahoma City, Oklahoma, killing 168.
- The Waco massacre prompts a nationwide debate in the U.S. about the freedom of association right of the Michigan Militia, Montana Militia and other radical groups.
- Crime levels in the U.S. peak in 1991, begin to fall afterwards to the lowest levels since the late 1960s at end of decade.
- Drug use in the U.S. reaches an all-time low in 1992 before increasing, reaching its peak in 1997 before declining again.
- Princess Diana dies in a car accident in 1997. Debates of accident vs assassination rage.
- Mother Teresa, the Roman Catholic nun who won the Nobel Peace Prize, dies at age 87.
- 21-year-old Golfer Tiger Woods wins the Masters Tournament by a record 12 strokes; becoming the youngest and first African-American to win the Masters.
- The Omagh bombing in Omagh, County Tyrone, Ireland which kills 29 civilians (including a woman pregnant with twins) and injures hundreds more.
- John F. Kennedy, Jr., his wife Carolyn Bessette and sister-in-law Lauren Bessette are killed when Kennedy's private plane crashes off the coast of Martha's Vineyard.
- American cyclist Lance Armstrong wins his first Tour de France in 1999, less than two years after battling testicular cancer.
- Beer keg registration becomes popular public policy in U.S.

People

World leaders

- Prime Minister Bob Hawke (Australia)
- Prime Minister Paul Keating (Australia)
- Prime Minister John Howard (Australia)
- President Fernando Affonso Collor de Mello (Brazil)
- President Itamar Franco (Brazil)
- President Fernando Henrique Cardoso (Brazil)
- Prime Minister Brian Mulroney (Canada)
- Prime Minister Kim Campbell (Canada)
- Prime Minister Jean Chrétien (Canada)
- "Paramount Leader" Deng Xiaoping (People's Republic of China)
- President Jiang Zemin (People's Republic of China)
- President Lee Teng-hui (Republic of China on Taiwan)
- President Franjo Tuđman (Croatia)
- Prime Minister Poul Nyrup Rasmussen (Denmark)
- President Hosni Mubarak (Egypt)
- President François Mitterrand (France)
- President Jacques Chirac (France)
- Chancellor Helmut Kohl (Germany)
- Chancellor Gerhard Schröder (Germany)
- Governor David Clive Wilson (Hong Kong (under British rule))
- Governor Christopher Francis Patten (Hong Kong (under British rule))
- Chief Executive Tung Chee Hwa (Hong Kong, People's Republic of China)
- Prime Minister Atal Bihari Vajpayee (India)
- President Mohammad Khatami (Iran)
- President Saddam Hussein (Iraq)
- Prime Minister Yitzhak Rabin (Israel)
- Prime Minister Benjamin Netanyahu (Israel)
- Emperor Akihito (Japan)
- Governor Vasco Joaquim Rocha Vieira (Macau (under Portuguese rule))
- Chief Executive Edmund Ho (Macau, People's Republic of China)
- President Yasser Arafat (Palestinian Authority)
- Pope Pope John Paul II
- President Corazon Aquino (Philippines)
- President Fidel Ramos (Philippines)
- President Joseph Estrada (Philippines)
- Prime Minister Mike Moore (New Zealand)
- Prime Minister Jim Bolger (New Zealand)
- Prime Minister Jenny Shipley (New Zealand)
- Prime Minister Helen Clark (New Zealand)
- President Ion Iliescu (Romania)
- President Emil Constantinescu (Romania)
- President Boris Yeltsin (Russia)
- Taoiseach Charles Haughey (Republic of Ireland)
- Taoiseach Albert Reynolds (Republic of Ireland)
- Taoiseach John Bruton (Republic of Ireland)
- Taoiseach Bertie Ahern (Republic of Ireland)
- President Boris Yeltsin (Russia)
- President Wee Kim Wee (Singapore)
- President Ong Teng Cheong (Singapore)
- President Sellapan Ramanathan (Singapore)
- President Frederik Willem de Klerk (South Africa)
- President Nelson Mandela (South Africa)
- President Kim Dae-jung (South Korea)
- President Mikhail Gorbachev (Soviet Union)
- King Juan Carlos I (Spain)
- President Felipe González (Spain)
- President José María Aznar (Spain)
- Queen Elizabeth II (United Kingdom et al.)
- Prime Minister John Major (United Kingdom)
- Prime Minister Tony Blair (United Kingdom)
- President George H.W. Bush (United States)
- President Bill Clinton (United States)
- President Slobodan Milošević (Federal Republic of Yugoslavia)

Entertainers

Federal Republic of Yugoslavia] Federal Republic of Yugoslavia]] Federal Republic of Yugoslavia
- 2pac
- Ace of Base
- Adam Sandler
- Aaliyah
- Alice in Chains
- Alanis Morrissette (Jagged Little Pill)
- Annie Lennox
- Anthony Hopkins (The Silence of the Lambs, Titus)
- Ashley Judd
- Beavis and Butt-Head
- Ben Affleck (Good Will Hunting)
- Bill Hicks
- Billy Bob Thornton
- Boyz II Men
- Bret Hart
- Britney Spears
- Bruce Willis (the Die Hard series, Pulp Fiction)
- Mariah Carey
- Dana Carvey (Wayne's World)
- Dean Cain
- Carmen Electra
- Christina Aguilera
- Cuba Gooding Jr (Boyz N the Hood, Jerry Maguire)
- Amy Grant
- Dave Matthews Band
- Demi Moore (Ghost, Striptease, A Few Good Men)
- Denzel Washington ( Malcolm X, Mo' Better Blues, Philadelphia)
- Destiny's Child (Destiny's Child, The Writing's On The Wall)
- Ellen DeGeneres (Ellen)
- Elizabeth Berkley (Saved by the Bell, Showgirls)
- Eurythmics
- Friends
- Courtney Cox
- Jennifer Aniston
- Lisa Kudrow
- Matt LeBlanc
- Matthew Perry
- David Schwimmer
- The Fugees
- Green Day (Dookie, Nimrod)
- Gwyneth Paltrow (Shakespeare in Love, The Talented Mr. Ripley, Se7en)
- Liam Gallagher of Oasis
- Noel Gallagher of Oasis
- Teri Hatcher
- Whitney Houston (The Bodyguard, Waiting to Exhale)
- Halle Berry (Introducing Dorothy Dandridge,Bullworth)
- Hanson
- Harrison Ford
- Helen Hunt (Mad About You, Twister, As Good as It Gets)
- Hootie & The Blowfish
- Jack Nicholson
- Jerry Seinfeld (Seinfeld)
- Jerry Springer
- Jim Carrey (Ace Ventura: Pet Detective, The Mask)
- Julia Roberts (Pretty Woman, Notting Hill)
- Kate Winslet (Titanic)
- Keanu Reeves (The Matrix)
- Kurt Cobain
- Leonardo DiCaprio (Titanic)
- Liam Neeson
- Macaulay Culkin (Home Alone)
- The Undertaker
- Martin Lawrence (House Party, Martin, Bad Boys)
- Mary J Blige (What's the 411?)
- Matt Damon (Good Will Hunting)
- Meg Ryan
- Mel Gibson (Braveheart)
- Michael Jackson
- Michael Keaton
- Michelle Pfeiffer (The Age of Innocence, Batman Returns)
- Mike Myers (Wayne's World, Saturday Night Live, Austin Powers)
- Mira Sorvino
- Nicole Kidman (My Life, Eyes Wide Shut)
- Notorious B.I.G.
- Nirvana
- Oasis
- Phil Collins
- Pamela Anderson (Baywatch)
- Pearl Jam
- "Image:Princesymbol.png" The artist formerly known as Prince
- Queen Latifah (Living Single, Set It Off)
- Quentin Tarantino (Pulp Fiction)
- Ralph Fiennes (Schindler's List, The English Patient)
- Jeri Ryan (Star Trek: Voyager)
- Samuel L. Jackson (Goodfellas, Pulp Fiction)
- Sandra Bullock (Speed, A Time to Kill)
- Shawn Michaels
- Spice Girls
- Stone Cold Steve Austin
- Tim Burton (Edward Scissorhands, Batman Returns)
- Tiffani-Amber Thiessen (Saved by the Bell, Beverly Hills 90210 )
- TLC (Lisa "Left-Eye" Lopes, T-Boz, Rozonda "Chilli" Thomas)
- Tom Hanks (Forrest Gump, Saving Private Ryan, Philadelphia, Toy Story, The Green Mile)
- Toni Braxton ( Toni Braxton (album) )
- U2 (Achtung Baby)
- Uma Thurman (Pulp Fiction)
- Whoopi Goldberg (Sister Act, Ghost, Ghosts of Mississippi, Hollywood Squares)
- Will Smith (The Fresh Prince of Bel Air, Men In Black)

Films

See also: 1990s in film

Books & Literature

Sports figures

Synthesis

:: This is an article about the philosophical concept. For information regarding the magazine, see Synthesis (Magazine) Synthesis (from the Greek words syn = plus and thesis = position) is commonly understood to be an integration of two or more pre-existing elements which results in a new creation.

Philosophical synthesis

The term is broad in meaning and can apply to physical, ideological, and/or phenomenological entities. In dialectics, synthesis is the final result of attempts to reconcile the inherent contradiction between thesis and antithesis. Along with the similar concept of integration, synthesis is generally considered to be an important element of modern philosophy, particularly in the various emerging ideas often considered to be holistic (as opposed to reductionistic).

Chemical synthesis

In chemistry, chemical synthesis is the process of forming a particular molecule from chemical precursors.

Synthesis in electronics and acoustics

In electronic musical instruments, sound synthesis is the method of sound generation a piece of hardware or software may employ, E.g. "Musically, "My lovely Access Virus B" mainly uses subtractive synthesis but it's got a bit of FM synthesis too." Modern electronic keyboard instruments are based around digital sound synthesizers that create audio waveforms that sound like they came from a violin or koto, without an actual violin or koto, because the sound is synthesized. A Video Synthesizer electronically creates TV signals without necessarily requiring the use of a TV camera. Moving abstract patterns, text subtitles, colorized or processed camera images can all be in the output of a video synthesizer. Analog video synthesizers included the Sandin Image Processor, the Rutt-Etra, Steve Beck's "Beck Direct" Synthesizer, Bill Hearn's colorizer, and the seminal work of Nam Jun Paik. Early digital synthesizers included Stephen Beck's Video Weavings, the 2901 bit slice processor from Steina and Woody Vasulka with Schier and Dosch, Sandin's Digital Image Colorizer, Etra's "Kangaroo Giant Box" , and the Fluidigeo Synthesizer. Documentation on the history of video synthesizers can also be found at http://www.experimentaltvcenter.org/history/index.html. In the world of electronic design automation, synthesis is the process of converting a digital design written in a hardware description language (HDL) into a low-level implementation consisting of primitive logic gates. Most large integrated circuits designed today are written in an HDL and "compiled" using a synthesis product. The first (and still most popular) synthesis tool was written by Synopsys.

External links

- [http://www.swemorph.com/pdf/anaeng-r.pdf Analysis and Synthesis: On Scientific Method based on a study by Bernhard Riemann] From the Swedish Morphological Society.

Evolutionary biology

Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change over time, i.e. their evolution. One who studies evolutionary biology is known as an evolutionary biologist, or less frequently evolutionist. Evolutionary biology is an interdisciplinary field because it includes scientists from many traditional taxonomically-oriented disciplines. For example, it generally includes scientists who may have a specialist training in particular organisms such as mammalogy, ornithology, or herpetology but use those organisms as systems to answer general questions in evolution. It also generally includes paleontologists who use fossils to answer questions about the mode and tempo of evolution, as well as theoreticians in areas such as population genetics and evolutionary theory. In the 1990s developmental biology made a re-entry into evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Its findings feed strongly into the new disciplines that study mankind's sociocultural evolution and evolutionary psychology during the millenia before the invention of agriculture. Evolutionary biology's frameworks of ideas and conceptual tools are now finding application in the study of a range of subjects from computing to nanotechnology. Artificial life is a subfield of Bioinformatics that attempts to model, or even recreate, the evolution of organisms as described by evolutionary biology. Usually this is done through mathematics and computer models.

History

Main article: History of evolutionary thought Evolutionary biology as an academic discipline in its own right emerged as a result of the modern evolutionary synthesis in the 1930s and 1940s. It was not until the 1970s and 1980s, however, that a significant number of universities had departments that specifically included the term evolutionary biology in their titles. In the United States, as a result of the rapid growth of molecular and cell biology, many universities have split (or aggregated) their biology departments into molecular and cell biology-style departments and ecology and evolutionary biology-style departments (which often have subsumed older departments in paleontology, zoology and the like). Microbiology has recently developed into an evolutionary discipline. It was originally ignored due to the paucity of morphological traits and the lack of a species concept in microbiology. Now, evolutionary researchers are taking advantage our extensive understanding of microbial physiology, the ease of microbial genomics, and the quick generation time of some microbes to answer evolutionary questions. Similar features have led to progress in viral evolution, particularly for bacteriophage.

Notable evolutionary biologists

Notable contributors to evolutionary biology include:
- James F. Crow
- Charles Darwin
- Erasmus Darwin
- Richard Dawkins
- Theodosius Dobzhansky
- Niles Eldredge
- Paul W. Ewald
- Ronald Fisher
- Douglas Futuyma
- Stephen Jay Gould
- J.B.S. Haldane
- W.D. "Bill" Hamilton
- Steve Jones
- Motoo Kimura
- Jean-Baptiste Lamarck
- Richard Lewontin
- Pierre Louis Maupertuis
- Lynn Margulis
- Ernst Mayr
- John Maynard Smith
- Tomoko Ohta
- Geerat Vermeij
- Alfred Russel Wallace
- David B. Weishampel
- George C. Williams
- Allan Wilson
- Edward Osborne Wilson
- Sewall Wright Notable popularizers of evolution whose research isn't primarily concerned with evolutionary biology include:
- Daniel Dennett
- Steven Pinker
- Carl Sagan

Bibliography

Textbooks

- Douglas J. Futuyma, Evolutionary Biology (3rd Edition), Sinauer Associates (1998) ISBN 0878931899
- Douglas J. Futuyma, Evolution, Sinauer Associates (2005) ISBN 0878931872
- Mark Ridley, Evolution (3rd edition), Blackwell (2003) ISBN 1405103450
- Scott Freeman and Jon Herron, Evolutionary Analysis, Prentice Hall (2003) ISBN 0131018590
- Monroe W. Strickberger, Evolution (3rd Edition), Jones & Bartlett Publishers (2000) ISBN 0763710660
- Michael R. Rose and Laurence D. Mueller, Evolution and Ecology of the Organism, Prentice Hall (2005) ISBN 0130104043

Notable monographs and other works

(only author, date of publication and title listed here, see the article for publication details)
- Charles Darwin (1859) The Origin of Species and (1871) The Descent of Man and Selection in Relation to Sex
- Ronald Fisher (1930) The Genetical Theory of Natural Selection
- John Maynard Smith and Eörs Szathmáry (1997) The Major Transitions in Evolution
- Important publications in evolutionary biology.
- :Category:Notable publications in evolutionary biology

Topics in evolutionary biology

- Foster's rule
- Muller's ratchet
- Mutational meltdown
- Fitness landscape
- List of other evolutionary biology topics
- ko:진화생물학

Category:Biology

Biology is the science of life. It is concerned with the characteristics and behaviors of organisms; how individuals come into existence, and how species evolve; and the interactions they have with each other and with their environment. Biology encompasses a broad spectrum of academic fields that are often considered independent disciplines many of which are listed below as subcategories. Category:Life Category:Science Category:Environmental science Category:Academic disciplines ko:분류:생물학 ms:Category:Biologi ja:Category:生物学 simple:Category:Biology

Executor-class Star Dreadnought

Star Destroyers are the iconic vessels of the Galactic Empire within the movie saga and fictional universe of Star Wars. Within the story line of the saga, Star Destroyers are depicted as Warships, large and dagger-shaped and extremely well-armed, serving in the thousands in the immense Imperial Starfleet and elsewhere, including in the service of the Galactic Republic, the New Republic, the Galactic Federation of Free Alliances - and possibly even in the corporate war fleets of the Confederacy of Independent Systems.

Imperial Star Destroyer

Confederacy of Independent Systems The term "Star Destroyer" most often refers to the iconic dagger-hulled combat vessels used by the Empire in the three films of the original Star Wars trilogy. These ships are commonly referred to as Imperial-class Star Destroyers, however, their offical title is Imperator-class (See section below). Within wider Star Wars lore, including the expanded universe, these "Imperial-class Star Destroyers" are likewise regarded as the definitive class of Star Destroyer, and one of the most important symbols of the Galactic Empire, serving the Imperial fleet for at least five decades. When the term "Star Destroyer" is used without further qualification, it usually refers to ships of this class. All Imperial-class variants are said to be 1,600 meters long (approximately one mile), with three large, and four small engines capable of accelerating the ship with a force of several thousand g and a hyperdrive capable of carrying them across the galaxy in a matter of weeks. Imperial-class Star Destroyers have a complement of at least 37,000 officers and crew. This would include officers, technicians and computer operators, fighter pilots, and support-craft crew, but apparently not the division of 9,700 stormtroopers ("Imperial Marines")— an overall total of 46,700 men. In service with the New Republic (forged by the heroes of the Rebel Alliance after the end of the movie saga) the crews were reduced to about 28,000 men. Star Wars lore says that two subtypes of Star Destroyer exist, the Mark I and Mark II designs—a distinction that seems to reflect the two distinct VFX models used in the Star Wars films; visually, the main difference between these is the tractor-beam array on the very top of the superstructure - on a Mark I ship, the tractor beam array is a tall, X-shaped structure, while the Mark II has a smaller array that looks somewhat like a table. Other notable variations include differences in weaponry (discussed below), and three small baffles arranged 60° apart around the main exhaust nozzles at the stern of the ISD-I.

Weapons

A single Star Destroyer is said to have sufficient firepower to overwhelm almost any warship deployed by enemies of the Empire, and to be capable of reducing a hostile planet to an uninhabitable ball of slag. However, some Rebel Alliance ships are more powerful than an Imperial-class Star Destroyer, including the Mon Calamari flagship "Home One". The earlier of the two VFX models, used in all three films in the original Star Wars trilogy, carries batteries of four massive double-barrelled turrets either side of the main superstructure, with smaller gun-emplacements on the centerline and in the notches on the edge of the hull. The second model, used in The Empire Strikes Back, lacks the smaller emplacements, and place of the large twin-turrets, it has eight-barrelled guns in open mountings. The Expanded Universe, however, attributes to the ISD-I an armament of 60 "turbolasers" and 60 "ion cannon", while that of the ISD-II is said to be 100 turbolasers and 20 ion cannon; missile weapons and smaller defensive guns are also mentioned in some sources. The exact relationship between the visible weapons and those described in text sources is unclear, however and different fans espouse different methods of dealing with the evidence. Each ship also carried a wing of 72 Imperial TIE, 12 TIE interceptors, and 12 TIE Bombers. At least one ship,NRS Rebel Dream, featured an enlarged hangar bay, but it is unknown if a greater number of fighters were carried. Several thousand troops were also stationed aboard along with a prefabricated base for rapid subjugation of rebellious territories. The ships also carried massive war vehicles like 20 AT-ATs and 30 AT-ST walkers. According to sources from the Expanded Universe, Imperial Star Destroyers also carried support craft and drop ships such as the Y85 Titan Dropship and the Sentinel-class Shuttle. The ship could also deploy TIE Fighters and orbital bombardment to support any surface action.

Imperator or Imperial?

While most Star Wars lore describes the iconic Star Destroyer as an "Imperial-class" ship, an alternative designation Imperator-class also exists, and the priority of the two names is a source of contention between some fans. The Imperator-class name apparently originates in a set of blueprints produced in 1978 attributed to "[http://www.geoffreymandel.com/ Geoffrey Mandel]" and packaged with Lucasfilm copyright. One Geoffrey Mandel, possibly the same man, is a well-known TV and film graphic artist, perhaps best-known for his work on [http://memory-alpha.org/en/wiki/Geoffrey_Mandel Star Trek]. However some fans allege that in 1978 he was a nineteen-year-old fan. These fans — proponents for the second-generation "Imperial-class" literature — allege that the blueprints were a work of fan-art (albeit a high-quality piece). In further support, they cite the differences b/w the drawings and the actual ISD. However the Lucasfilm copyright marks on the packaging undermine this conspiracy theory. Furthermore, differences between the drawing and the actual ISD is not necesarily an argument for its non-canonicity, because other non-controversially official drawings and spec sheets (such as those in the ISB or EGVV) also do not match up (see Executor section below) with the "real" (as in G-canon) version. Tangentially, Mandel is also said to be the originator of the "D-7" designation for the classic Klingon battle-cruiser from Star Trek, making him responsible for the official in-universe designations of the iconic enemy ships of the two great sci-fi franchises. Copies of Mandel's blueprints continued to circulate in fandom and collector shops. Twenty years later, they were recognized as "rare but official" early material by online fans including the [http://theforce.net/swtc/isd.html Star Wars Technical Commentaries] website. The label was subsequently reaffirmed and reconciled in the Incredible Cross-Sections guide for Revenge of the Sith: it explains that "Imperator-class" was the original, 'correct' designation, but was politically re-dubbed Imperial-class Star Destroyer after the Jedi Purge. The Imperial-class designation, which seems to have originated in Star Wars Role-playing game material in the later 1980s, remains the designation used in most official material. Incredible Cross-Sections allows that the type was renamed to Imperial-class following the declaration of the Galactic Empire by Palpatine, while the official [http://www.starwars.com/databank/starship/republicattackcruiser/?id=eu Star Wars Databank] leaves the exact relationship between the prototype Imperator-class and the iconic Imperial-class of the movies somewhat vague. The two names will be used interchangeably in this document, since both versions occur in the official literature, and their coexistence has been retrospectively explained within the Star Wars universe.

Features

Main bridge

Palpatine The main bridge of all known Imperial ships has the same basic layout. The outer-most part features nine triangular viewports. The center contains two crewpits which house the control consoles for the ship, between which is the command walkway. To the right and left sides of the bridge are two alcoves containing the weapons and defense stations. Behind the bridge are the communications stations, a turbolift, and a HoloNet pod for ship-to-ship communications. On the level directly beneath the bridge is the main navigation complex.

Weapons

A single Star Destroyer is said to have sufficient firepower to overwhelm almost any warship deployed by enemies of the Empire, and to be capable of reducing a hostile planet to an uninhabitable ball of slag. However, some Rebel Alliance ships are more powerful than an Imperial-class Star Destroyer, including the Mon Calamari flagship Home One. The earlier of the two VFX models, used in all three films in the original Star Wars trilogy, carries batteries of four massive double-barrelled turrets either side of the main superstructure, with smaller gun-emplacements on the centerline and in the notches on the edge of the hull. The second model, used in The Empire Strikes Back, lacks the smaller emplacements, and place of the large twin-turrets, it has eight-barrelled guns in open mountings. The Expanded Universe, however, attributes to the ISD-I an armament of 60 "turbolasers" and 60 "ion cannon", while that of the ISD-II is said to be 100 turbolasers and 20 ion cannon; missile weapons and smaller defensive guns are also mentioned in some sources. The exact relationship between the visible weapons and those described in text sources is unclear, however and different fans espouse different methods of dealing with the evidence. Each ship also carried a wing of 72 Imperial TIE, 12 TIE interceptors, and 12 TIE Bombers. At least one ship,NRS Rebel Dream, featured an enlarged hangar bay, but it is unknown if a greater number of fighters were carried. Several thousand troops were also stationed aboard along with a prefabricated base for rapid subjugation of rebellious territories. The ships also carried massive war vehicles like 20 AT-ATs and 30 AT-ST walkers. According to sources from the Expanded Universe, Imperial Star Destroyers also carried support craft and drop ships such as the Y85 Titan Dropship and the Sentinel-class Shuttle. The ship could also deploy TIE Fighters and orbital bombardment to support any surface action.

Sensor globes or shield generators?

The geodesic domes located on and around the bridge superstructure of Star Destroyers and related ships are the topic of much debate. Are they shield generators or sensor domes? When the Executor's globe exploded during the Battle of Endor, a crewman said that the shields were down. Many people attributed this to the dome being destroyed. Others disagreed since Admiral Ackbar gave the order to "concentrate all fire on that Super Star Destroyer". Many took that to mean that the shields were already down when the fighters attacked. Others, however, noted that aside from the A-wings firing their concussion missiles at the globes, there were no other ships firing on the Executor, either before or after its shields were down. Inside the Worlds of Star Wars shows the bridge area of the Executor and declares the globes to be sensor globes. However it does also show that there are backup bridge shield generators built into the base of the domes. The loss of one of these globes could mean that the crew was not able to bring the backup bridge shield generators back online in time or at all. Also the fact that the A-wings were able to destroy the sensor globe, without exploding against the shields, indicates that the shields may have been down. Others, however, don't seem to use that as an indication, saying that Star Destroyer shields are hull hugging, instead of bubble-like. Earlier in the battle a Y-wing can be observed slamming into a Star Destroyer; a flash of light occurs when it hits. Many feel that this flash of light is the shields. Many older reference books such as The Essential Guide to Vehicles and Vessels and The Essential Guide to Weapons and Technology also label the pair of globes on top of the bridge as "Deflector Shield Generators". The use of the globes as shield generators is also evident in most of LucasArts' X-Wing and TIE Fighter computer games, where the shields of a Star Destroyer are knocked out if the two generators above the bridge are destroyed. The use of this has been noted in several sources as a means of giving the player a better chance of defeating a Star Destroyer.

Vulnerable underbelly?

In the Thrawn Trilogy written by Timothy Zahn, when Luke Skywalker, Han Solo, Garm Bel Iblis, Talon Karrde, Mara Jade, Wedge Antilles, and Leia Organa Solo were trying to capture the Katana Fleet, Imperial Star Destroyers were involved in a battle. it was said that the forward ventral sensors were knocked out, thus giving the pirates "free rein of the Star Destroyer's underside". This implies that there are only two sensor stations that are solely responsible for targeting and detection.

Areas of service

Imperial service

Within the fictional universe of Star Wars, Imperial-class Star Destroyers had a distinguished career in the Imperial Starfleet, where they symbolized the Empire's military might, for better or worse. The name of the prototype Imperator, bestowed in the last years of the Old Republic, is in the real-world the Latin word for commander as well as emperor, and later names such as Imperial and Empire (the name of the lead ship of the Mark II subclass) stressed the role of the class as primary instruments of military autocracy. The crews of Imperial-class ships were comprised of the elite of the Imperial Navy, but the exact number of these ships in service is disputed among fans. No more than about forty are seen on-screen in Return of the Jedi, but according to official lore, the Imperial Fleet contained more than 25,000 Star Destroyers at its greatest strength, and this "canonical" figure is probably accepted by the majority of fans. Some, however, prefer fanon figures as high as several million Imperial-class vessels in service at the Empire's height of power, while others argue that no more than a few thousand of the 25,000 Star Destroyers were necessarily Imperial-class ships, with the majority being smaller types such as Victory-class ships. Many Star Destroyers were destroyed in the fratricidal warfare that consumed the Empire after the death of Emperor Palpatine at Endor, while others defected to, or were captured by, the Rebels. The majority of the surrendered vessels were decommissioned, but some remained in service (see below). In the Star Wars movies and in the Expanded Universe alike, the ISD serves a visible role in the Imperial starfleet. Expanded Universe lore identifies Imperial-class ships as the centerpiece of Superiority Fleets, the formations used by local sector-level forces to scour Imperial space clear of enemy warships like those of the Rebel Alliance. Within each Superiority Fleet, six ISDs typically served as the command ships for component formations known as "Battle Squadrons", but sister-ships have also been observed to operate more or less independently, or in pairs as guard ships on important worlds. By the time of the final peace between the remnants of the Empire and the heirs of the Rebellion, the eight remaining sector fleets of what was left of Imperial Space still centered around the Imperial-class Star Destroyer, with around a dozen such ships per Sector, but they often operated as battle lines without support from smaller vessels, and may have been refitted to carry more defensive weaponry on their own hulls, making them more capable of fending off fighter and gunship attack. More controversial is the ISD's role on higher levels. Some fans argue that these ships were mere support ships, equating them with real-life destroyers. Much larger ships appear within the Star Wars saga, corresponding to cruiser and battleship designations. However, as a confusing result of merchandising inertia, even the largest of these are often colloquially called "Star Destroyers". Scores of Imperial-class ships are shown as forming the vanguard of some Imperial battle-fleets. For instance, at the Battle of Endor in Return of the Jedi, there were about forty Imperial-class destroyers and one Super Star Destroyer. In other Star Wars lore, the battlefleet charged with defending the Imperial Core Worlds had one Super Star Destroyer and fifty-seven other capital ships, while Grand Admiral Josef Grunger's fleet consisted of one Super Star Destroyer, thirty Star Destroyers, and almost 200 smaller ships, and the fleet assembled by Admiral Daala included one Super Star Destroyer, more than forty Imperial-class ships, and more than a hundred Victory-class ships. The fleet at the center of the Empire's strategies for defending the Outer Rim, Black Sword Command, contained about forty Imperial-class and Victory-class Star Destroyers and three Super Star Destroyers, but one of these SSDs was simply fitting out at a shipyard within the command's jurisdiction, and it is not impossible that at least one of the others was merely under construction. These fleet compositions resemble the realistic ratios of small destroyers to large battleships in navies of the mid 20th Century Earth.

New Republic service

Within the Star Wars story line, the Imperial-class Star Destroyer has also appeared in the forces of other space-defense navies. For instance, a number were commissioned into the private defense-fleet of the shipyard system of Kuat where they were initially designed, while the independent monarchy that ruled the Hapes Star Cluster was able to seize some vessels during their war against Imperial occupation. But after the Empire, Star Destroyers were most visible in the armadas of the New Republic, the successor-state formed by the heroes of the Rebellion such as Princess Leia, Luke Skywalker, and Han Solo. The refits implemented by that government seem to have often involved structural modifications, and generally entailed the use of a much smaller crew. The capability to deploy planetary-assault soldiers appears to have been ignored, as the Republic had a general military doctrine less based on armies of occupation, and endurance was reduced from six years to six months, as the New Republic Defense Force doctrine operated ships on relatively short patrols before returning to base. Despite their stellar qualities, however, the Imperial-class was apparently too much of a symbol of Imperial might, at least initially, to deploy in large numbers. Many of those used by the heirs of the Rebellion were symbolically high-profile prizes of war, such as the Accuser and Adjudicator captured at the Battle of Endor, the Avarice which defected during the Bacta War, and the Tyrant which had once been part of Darth Vader's personal fleet—renamed Emancipator, Liberator, Freedom and Rebel Dream respectively. For the most part, the New Republic chose to procure Mon Calamari Star Cruisers instead, and descendants of the Victory-class Star Destroyer were procured in quantity however, perhaps because the Victory was a symbol of the Old Republic's military machine, or perhaps more simply because its designer had joined the Rebellion, whereas the creators of the Imperial-class ship remained loyal to the Empire. In later years, however, after the end of the Galactic Civil War, the use of Imperial-class ships apparently became regarded as much more acceptable to the heirs of the Rebellion, with many new ships like the Mon Mothma being named for former heroes of the Rebel Alliance.

Private service

Within the Expanded Universe, one Imperial-class Star Destroyer is in private hands, the Errant Venture (formerly the HIMS Virulence), captained by the smuggler and rogue Booster Terrik. It was captured several years after the Battle of Endor during the Bacta War against Ysanne Isard, but was in poor condition for many years owing to the great cost of maintaining such a large vessel, and it had been stripped of the vast majority of her armament: only ten turbolasers were permitted, and even those were not always functional. Years later, she received a comprehensive refit in exchange for use in a New Republic special-operations raid on an Imperial base, including a deep red paint job to replace the classic Imperial white. While Captain Terrik was not permitted to keep all of his weapons after the operation, they were reinstated during the Yuuzhan Vong invasion, and, according to rumor, were augmented by a ship-killing superlaser. During the Vong invasion, the Errant Venture served as a temporary Jedi sanctuary and also as squadron flagship in the forces that rallied to defeat the Yuuzhan Vong. No other demilitarized and nominally civilian Star Destroyers in are known to exist, although in practice, some ex-Imperial ships like the pirate flagship Invidious were little different in their capabilities than the Errant Venture at some stages of her career.

Individual ship names

See List of capital ships in Star Wars: X-wing for the names of some of the Imperial-class Star Destroyers in service before the Battle of Hoth.

Other Star Destroyers

Of course, the iconic Imperial Star Destroyer is not the only "Star Destroyer" in Star Wars: in the movies alone, the Venator-class attack cruisers of Episode III, Darth Vader's massive command ship Executor, and even the cigar-shaped Separatist flagship [http://en.wikipedia.org/wiki/Trade_Federation_Cruiser The Invisible Hand], all have a claim to be considered as "Star Destroyers". Additionally, beyond being big, dagger-shaped warships in Star Wars, it has proved hard to find a precise definition of the term "Star Destroyer" that satisfies all of the franchise's fans. Most official products call the Imperial Star Destroyer, arguably the most famous of the group, either a cruiser or a battleship, but some fans believe that a "Star Destroyer" must be a destroyer in the traditional naval sense, and that such a destroyer must be a relatively small ship. Both of these claims are questioned by other fans, but it must be admitted that the largest Star Destroyers are many, many times bigger than the standard Imperial-class ships, and at least some of these larger Star Destroyers are known alternatively as Star Dreadnoughts. In the original draft scripts of the movie that would become Star Wars, it can be noted that the term "Stardestroyer" (as a compound word) was used for the two-man fighters flown by what would become the Galactic Empire in the final movie.

Old Republic Star Destroyers

Within Star Wars lore, while similar dagger-hulled warships are said to have existed for thousands of years, the earliest ships called "Star Destroyers" are the 900m Victory-class and the 1,137m Venator-class, deployed by the Galactic Republic during the Clone Wars, the conflict which saw that once-democratic federation transformed into the autocratic Empire. Although the two were comparable in size and power, each had distinct characteristics and abilities that the other lacked. These vessels were also employed by the fledgling Empire, but the Venator-class were later phased out in favor of larger and more powerful designs.

Victory-class Star Destroyer

The Victory-class Star Destroyer was designed by Rendili Stardrive to compete with Kuat Drive Yards and the successful Acclamator long-range military assault transport. They were the most powerful medium combatants of the Galactic Republic's military machine during the Clone Wars. The Republic and fledgling Empire bought them and their competitor, KDY's Venator-class Star Destroyer, in great numbers. Ships of the Victory class are 900 meters long and possess three primary ion drives for sub-light propulsion. However, they are somewhat sluggish spacecraft and even later refits never really fixed that design flaw. The first flight of ships was capable of independent flight in atmosphere; in one of the most infamous examples of this capability, then-Captain Tarkin landed his vessel on a crowd of protestors in what would later be called the Ghorman Massacre. The second flight was not capable of effective atmospheric operations. The Victory-I subclass included eighty concussion missile tubes, while the rarely produced Victory-II subclass lacked them in favour of ion cannons. The Victory-II also had faster sub-light drives for better space-to-space combat and lost its atmospheric capability, perhaps making it an even closer predecessor to the Imperial-class Star Destroyers that followed. All ships carried two squadrons of star-fighters. Presumably there are heavy weapons turrets flanking the command tower but they have never been explicitly shown in the official literature. With the rise of the Empire, the Victory was replaced in general service by the Imperator-class Star Destroyer, a much more capable design. Many Victory-class ships were sold off (many to the Corporate Sector) or decommissioned. (Note however, that the Victory class still saw a lot of action against Rebels and pirate groups and that there was still some production.) After the end of the civil war, the Imperial-class destroyer (formerly Imperator-class) was seen by some in the New Republic government as too much a reminder of the Empire. Under Mon Mothma, the New Republic concentrated on developing new ships based on the Victory-class design - which was seen as more of a product of the Old Republic that preceded the Empire. The design lineage lives on in the Republic and Defender (also known as Nebula and Obi-Wan) class Star Destroyers in service with the New Republic. One notable feature of the Victory-class is that it is one of the largest ships capable of operating effectively in the atmosphere of a planet. This gives it an advantage over its larger cousins in planetary assault scenarios, where it can be used to provide close-support for ground forces, and to intimidate the enemy. This advantage did not prevent it from being phased out and replaced by new classes as the main warship of the Empire, but it did ensure that the Victory was often assigned to invasion or policing fleets to make use of this ability. The Victory-class Star Destroyer was apparently part of Lucas's original trilogy universe (Episode IV-VI) and was mentioned in the 1980s Star Wars Sourcebook. However, the Victory was never seen in the original Trilogy or Episode III, despite being widely recognized as the direct predecessor to the Imperial-class in many sources (including the Essential Guide to Vessels and Vehicles, published before the release of Phantom Menace). It was perhaps because the Victory's wings and bridge/tower nodes seem like ugly additions to the otherwise sleek design and clean lines of the Imperial-class. (Otherwise, the Victory is very similar to the Imperial in looks). The Acclamator and Venator-class ships, however, were created for Episodes II and III, and never existed in any literature prior to the release of those movies.

Venator-class Star Destroyer

New Republic Nicknamed the "Republic Attack Cruiser", the Venator-class Star Destroyer was based from the success of the Acclamator-class assault transport and the Victory-class Star Destroyer. While the Acclamator was primarily an armed troop transport and the Victory was a jack-of-all-trades, the Venator was primarily a starfighter carrier/destroyer. The Venator-class destroyer was 1,137 meters long and carried a crew of 7,400. Its main reactor could consume up to 40,000 tons of fuel per second and had engines that could accelerate the massive vessel at 30,000 m/s². The ship is capable of operating within atmospheres and landing for docking as well retrieving/disembarking the ground forces. The Venator-class carried upwards of 400 starfighters in its large hangar bays, a feature phased out of successor destroyer designs in favor of heavier weapons on the ships themselves. Standard fighter complement was 192 V-Wing starfighters, 192 Eta-2 Actis Interceptors, and 36 ARC-170 starfighters. 40 LAAT/i gunships and 24 AT-TE walkers were carried for ground operations. Combined with its fighters, the Venator's powerful engines, strong deflector shields and armament consisting of 8 heavy turbolaser turrets, 2 medium dual turbolaser cannons, 52 point-defense laser cannons, and 4 heavy proton torpedo tubes made it one of the most powerful and fearsome medium warships of the time. Venator-class Star Destroyers were deployed in a number of battles during the Clone Wars, most notably during the Battle of Coruscant when upwards of a thousand of the ships helped protect the capital. As the Galactic Republic transformed into the Galactic Empire, the Venator ceased production in favor of the newer Imperator-class Star Destroyer, a warship even more deadly than the Venator. Thousands of ships were procured during the Clone Wars, then slowly mothballed over the succeeding decade. The Venator-class is established as a destroyer, an escort, and a lighter vessel in the Revenge of the Sith Incredible Cross-Sections fact book, and recognized as canon by LFL. The name, Venator, comes from Latin and translates to both "Hunter" and "Skirmisher".

Confederacy of Independent Systems Star Destroyers

There exist a number of ships whose designation as Star Destroyers is contested. Those are chiefly the cigar-shaped Separatist cruisers seen in Revenge of the Sith, which are called Star Destroyers semi-colliqually and can be, for the purposes of this discussion, considered Star Destroyer-type ships. These ships are not, insofar as the community is aware, included in the Old Republic or Imperial arsenals as are all other period Star Destroyers. They remain components of the CIS starfleet.

Providence-class destroyer

:See Trade Federation Cruiser A type of ship used by the Trade Federation and the Confederacy of Independent Systems, this class was not the standard and more effective "dagger" shape favored by the Republic and later Empire. Instead it was a tapered cylinder, looking more like a Coruscanti skyscraper laid on its side then a warship. At 1,088 meters in length it was larger then the Republic's Victory class but smaller then star destroyers later fielded by the Republic. Capable of 2,500 Gs in open space and 2,000 kph in atmosphere, these craft lacked the direct power feeds from the reactor to the guns. As a result their offensive armerment had to be augmented with a large number of proton torpedo launchers. These ships apparently had limited hangar facilities, a limitation corrected in later modifications. There is some dispute as to whether this class is to be considered a "Star Destroyer". Critics claim that it was only called such "in passing" and raise the possibility of it being slang. Nevertheless, since there is no clear evidence against this designation, canon policy mandates we accept it as true, and the page will assume thus until proven otherwise.

Invisible Hand-type

:See Trade Federation Cruiser With a known production run of only 3 ships, this kind of craft saw limited use in the Clone Wars. When Viceroy Gunray commissioned this ship, he had them remove the aft reactors, fuel stores, and some of the engine components to make room for a massive hangar. The result was a significant weakening of the ship in return for an extravegant hangar facility. When General Grievous assumed command of Confederacy's armed forces, he siezed this ship as his personal vessel to insult the Viceroy, who had previously and repeatedly insulted him. Two sister ships were commissioned, the Lucid Voice and Collicoid Swarm, and they were used in a disinformation campaign to keep Republic spies unable to pinpoint Grievous' exact location. The modifications to this ship left it with a reduced and weakened armerment. It now carried only 14 quad turbolaser turrets, 34 dual laser cannons, 2 ion cannons, 12 point-defense ion cannons, 102 proton torpdo launchers, and an unknown number of point-defense flak cannons. It carried 240 droid starfighters, 160 Mobile Troop Transports, and 280 assorted droid vehicles. For infantry duty it caried up to 1.5 million deactivated droids, and had a crew of 600. In Revenge of the Sith: Incredible Cross-Sections, it is called in what is apparently intended to be a technical capacity a "Modified Providence-class carrier/destroyer". This class has a similar basis for its claim as a Star Destroyer as the Providence-class, and as such is similarly disputed by others.

Galactic Empire Star Destroyers

This section will obviously disclude the previously analyzed Imperial- or Imperator-class Star Destroyer (the two being one and the same). The most renowned user of Star Destroyer-type ships was the tyrannical Galactic Empire. The menacing profile of a huge Star Destroyer became a symbol of Imperial might and domination, and many Rebel convoys and even militarized armadas were punished by Imperial-class warships acting as sector defense ships and blockade enforcers, either with impoundment or total destruction (and sometimes both, as evidenced by the off-record capture and annihilation of the Tantive IV, consular ship of Princess Leia Organa). At nearly all major engagements of the war, Star Destroyers were present. The Navy's standard Imperial-class ship was 1,600 meters long, but the term "Star Destroyer" was also loosely applied as slang to larger ships, including massive star battleships stretching more than ten miles from bow to stern. For the purposes of this particular section, only sub-Imperial-class or ships roughly equal to the Imperial-class will be overviewed.

Tector-class Star Destroyer

Princess Leia Organa The existence of the Tector-class is established in the Revenge of the Sith Incredible Cross-Sections fact book. A Tector-class Star Destroyer may have been seen during the Battle of Endor. The alleged Tector-class was based on the Imperial-class hull, lacking the ventral hangar bay and visible reactor-bulb. It is a dedicated attack ship, and not a cruiser/carrier hybrid like the Imperial. The Millennium Falcon can be seen flying over this ship's belly in a scene in Return of the Jedi, also showing the only clear example of a capital ship being upside-down, relative to nearby ships, in a Star Wars movie (if the ship is a Tector as some do believe). Since it is never explicitly stated whether this ship shown is a Tector-class Star Destroyer or not (and no one has a diagram or confirmed photo of a Tector to use as a comparison), this article will not rule one way or the other on the matter. In the Roman army, Tector referred to a type of cavalry trooper equipped with a large shield, befitting a warship with extra armor - but the most common usage of the word was to describe an artisan who applied plaster finish to walls, the Roman equivalent of a house-painter.

Harrow-type

A Star Destroyer featuring Victory-like "wings" but an Imperial-class grade of hangar bay (fairly large) as well as several other cosmetic differences, the Harrow measured about the length of a Victory-class vessel (900 meters or thereabouts) and may have been a Kuat Drive Yards attempt to shoo competitor Rendili StarDrive's still-successful Victory out of the market with their own niche-fitting light Star Destroyer. Rogue Squadron encountered the Harrow, which seems unlikely to be a one-of-a-kind vessel, in orbit of Tatooine some months after the Battle of Endor, though with the confusion and chaos in the Imperial war machine following the Emperor's death, it would appear doubtful that the Harrow was constructed and put into service in the time following the Battle of Endor (meaning that it likely was introduced to the fleet during or before the height of the Galactic Civil War). The starship Harrow possessed two main sub-light engine drives and then two smaller ones between them stacked vertically. It was commanded as of the Tatooine mission by Captain Semtim, and judging by its mission (to recover supplies hidden by Grand Vizier Sate Pestage on Tatooine), size, and design similarities to the Victory-class Star Destroyer, was probably capable of travel through a planet's atmosphere. However, as with the conjecture on when it was introduced, there is no solid proof in one direction or the other.

Dominator-type

:See Interdictor Cruiser Characterized by its four gravity-well projectors as well as its "double bridge" tower, the Dominator was the command ship of Loka Hosk and its main body bore similarities to the standard Imperial-class line of warship. The Binder of Delak Krennel's forces was also of this type, as was an anonymous Interdictor in Thrawn's fleet. It seems quite safe to say that this ship, described in Star Wars Encyclopedia as an "interdictor Star Destroyer". As with the Harrow, it seems possible - maybe even probable - that this is a Kuat Drive Yards response to a ship developed by a rival manufacturer - in this case, the Immobilizer-418 built by Sienar Fleet Systems. The ship's true classification remains unknown, though it has been described as both a "cruiser" and a "dreadnought". While "cruiser" seems to be a catchall terminology for any starship larger than a starfighter (having been used in the Jedi Quest series of books to describe Mol Arcasite's ship, from context appearing to be something between being an assault starfighter on the smaller side or a larger, freighter-sized attack ship on the bigger), its size is similar to the 1,600-meter Imperial-class Star Destroyer, which fits the role of cruiser. As previously observed, though, attempts to class Star Wars warships by Earth sea navy standards are almost certainly doomed to failure. It can best be described, probably, in terms of naval role as a heavy interdiction cruiser. Some might refer to the Dominator-type as an Interdictor-class Star Destroyer, which may very well be the closest to an official name that we have. For now, it's listed as a Dominator-type interdictor Star Destroyer, but Dominator certainly isn't the only ship observed of this class. In the post-Endor period, however, it seems to be reasonably common (and as with the Harrow, its first sighting was mere months after the Imperial catastrophe over the Forest Moon, meaning that it was probably at least commissioned prior to then) though they haven't been overtly said to be used as of the Yuuzhan Vong invasion. New Republic/Galactic Alliance ships such as Elegos A'Kla and Mon Mothma, modified Imperial-class Star Destroyers Mark II with gravity-well projectors, seem to be filling their role quite admirably, and it seems that this as-yet anonymous interdictor Star Destroyer may have been phased out by that time, or at least too rare to be of much real value.

New Republic Star Destroyers

The defeat at Endor did not lead to the immediate destruction of the Imperial fleet, but it did mark the end of the Empire as the galaxy's dominant superpower. The victorious Rebel Alliance became the New Republic, and it began to build new Star Destroyers of its own. Although considerably more compact than Imperial-class Star Destroyers, these new ships rivaled them in firepower, armor, and combat capability.

Republic-class Star Destroyer

The Republic-class Star Destroyer was designed and built by Rendili StarDrive for the New Republic as a lower-cost destroyer. She only required a fifth of the crew, yet had firepower twenty percent greater than that of an Imperial. In addition, she was only half the cost and two Republics could defeat a single ISD. Fighter complement remained similar at six squadrons. However, the design almost certainly had much inferior endurance (perhaps as little as six months, compared to six years on the Imperial) and the extensive ground-assault complement of the Imperial was probably eliminated. The design had much more in common with the Victory-class Star Destroyer than the Imperial. In the Star Wars: Short Visionaries novel, in the Battle of Coruscant, one Republic-class Star Destroyer is seen right above General Grievous's flagship. This can likely be dismissed as artistic license, error, or otherwise deviance, since Republic-class Star Destroyers were nonexistent as of the end of the Clone Wars, and were for a good thirty-five or so years afterwards.

Nebula-class Star Destroyer

The Nebula-class Star Destroyer was designed by Republic Engineering Corporation as a relatively low-cost line warship for the New Republic as part of the New Class modernization program. Unlike most Star Destroyers, the Nebula deletes the large dorsal superstructure that had exemplified the design of most major warships for decades; instead, it had what appeared to be a small navigation bridge thus making the lines much smoother. In addition, the firepower was considered equal to that of the Imperial I-class Star Destroyer; its fighter complement consisted of one wing. Like most New Republic designs, the Nebula probably had endurance on the order of six months and virtually no ability to land troops.

Defender-class Star Destroyer

Republic Engineering Corporation Like the Nebula-class Star Destroyer, the Defender follows a design philosophy of sleekness, largely eliminating the protruding bridge tower and mostly internalizing shield generators. Defender-class vessels served with distinction during the Yuuzhan Vong invasion of the galaxy, participating in battles including the Battle of Ebaq 9 and the Battle of Yuuzhan'tar. They became favorites of New Republic military commanders and continued to gain in popularity through the formation of the Galactic Federation of Free Alliances under Cal Omas. Defenders measure a standard 1,040 meters in length, making them shorter than the elderly, long-retired Venator-class Star Destroyers, but have enough firepower to challenge ships as large and renowned for power as the Imperial-class and Tector-class Star Destroyers. It should be noted that some factions believe that the Defender- and Nebula-class Star Destroyers are actually one in the same, and oppose one another on what its formal name and designation is or should be.

Galactic Alliance Star Destroyers

After the dissolution of the New Republic following the doctored election of Cal Omas into office as Chief of State, the Galactic Federation of Free Alliances was formed under a new constitution. After finally defeating the despicable Yuuzhan Vong Empire and retaking their seat of government at Coruscant, they began to build a more modern and more flexible military arsenal, drawing on new technologies developed and provided for them by such companies as Tendrando Arms (run by the very same Lando Calrissian who helped rig the election to get Omas elected over anti-Jedi opponent Fyor Rodan). By the time of the Battle of the Murgo Choke, the GFFA was ready to face the Killiks with a newly updated and equipped fleet. Among this fleet's components numbered new Star Destroyer types. It is likely that, as the Expanded Universe ventures further into the future with The Swarm War, due December 2005, and the Legacy of the Force 9-book series beginning release in spring 2006, more ships will be added to this category.

Admiral Ackbar-type

Named after Ackbar, deceased former Supreme Commander of the New Republic Armed Forces, the Admiral Ackbar seems to be a Victory-class Star Destroyer with extensive modifications, probably enough to push it into being at least a subtype, not the least of which is a giant turret-mounted tractor beam generator sufficient enough to seize ships at a considerable distance and tow them in for handling by smaller and more precise beam generators capable of guiding them to the hangar bay. Commanded by Admiral Nek Bwau'tu, it captured the Millennium Falcon with Jedi and renowned heroines Leia Organa Solo and Saba Sebatyne aboard and impounded them for attempting to run a blockade against Killik-held worlds on the edge of the Unknown Regions. The Gorog Dark Nest of Killiks attacked and overwhelmed the Ackbar, using carefully planted assassin bugs inside the ship to incapacitate much of her crew during the assault, and Raynar Thul, ex-Jedi and leader of the "Colony" of Killiks, came aboard the ship to take personal command. Though Bwau'tu, Organa Solo, and Sebatyne escaped along with many crew members, a large fraction of the ship's personnel was not so lucky. Crew members unlucky or stupid enough to get in the assassin bug swarms' way were usually badly wounded, sometimes sickened, and often killed, and the Ackbar came under Killik control. Although the class of Ackbar is unstated as of The Unseen Queen, it seems that this flagship is not a unique vessel. Noghri bodyguard Cakhmaim identifies the Victory-class update as "one of the new pirate hunters" upon seeing it, implying that Admiral Ackbar isn't the only ship of this class.

Chiss Ascendancy Star Destroyers

An unnamed example of a Chiss-built Star Destroyer was sighted at Qoribu and Kr in The Joiner King. It is said to be somewhat larger than a Victory-class Star Destroyer, to which at first glance appeared to be the class of ship that this Chiss warship was to Jedi Knight Jaina Solo, but has more organic lines. It carries an unknown compliment of Chiss Clawcraft and is armed with conventional turbolaser weaponry.

Super Star Destroyers

The term "Super Star Destroyer", often abbreviated SSD, is a general term used to refer to any ship in the Galactic Empire's Starfleet using the wedge/dagger design aesthetic which is larger than the 1,600m long Imperator-class. As such, any ship listed below can be termed as a "Super Star Destroyer", whatever its more formal designation, and this is the most commonly taken path by Star Wars characters regardless of their alignment.

Allegiance-class Star Destroyer

The 2,200 meter long Allegiance-type Star Destroyer is a dedicated fleet destroyer with heavy armor and no hangar bay, similar to the Tector-class. Unlike the Tector, the Allegiances class has a large ventral bulb, implying a massive reactor and very powerful weapons and shields. The proper class name of this class is not known; Allegiance is the only named representative of the class. In the Dark Empire comics, ships of this class were seen at several major battles and were also the primary escorts of HIMS Eclipse. Allegiance was referred to as a "Super Star Destroyer", so it may be considered a light cruiser rather than a destroyer.

Executor-class Star Dreadnought

:Also referred to as Super-class Star Destroyer, Executor-class Star Destroyer, and Executor-class Super Star Destroyer in some sources; heading remains currently technically accurate and up-to-date Dark Empire Note: When used alone, the term "Super Star Destroyer" is most often used to denote this class. Newer source material indicates that the ~19,000 meter long Executor-class (according to LFL by Leland Chee and Inside the Worlds of the Star Wars Trilogy) carries over 5,000 turbolasers, ion cannons, and many wings of starfighters. The number of wings is unknown, but Darksaber sets the lower limit at some "thousands" of starfighters. The number of lesser weaponry such as point-defense laser cannon and missile weaponry has not been published. Two prefabricated garrison bases are also stored on board for rapid deployment. Her shields are said to be able to dissipate power output equal to a medium-sized star; in one comic, the shields are shown to protect the Executor from colliding with three Imperial-class Star Destroyers as they left hyperspace at relativistic speed. Despite its immense firepower, the ship was designed first and foremost as a mobile command and control center. Some sources have suggested that she may be a large battle-cruiser; however, the armor may be enough to be considered a battleship. The Executor-class includes Darth Vader's flagship the "Executor."

Past depictions of the Executor in the Expanded Universe

For some years, official literature placed curiously few weapons on ships of the Executor's class: only 250 turbolaser batteries, 250 heavy Turbolaser batteries, 250 ion cannons, and 250 concussion missile silos. Some of the later versions also have 40 tractor beam emplacements. 144 starfighters (2 wings) were said to be carried. In addition, typical depictions tend to draw only 9, instead of the 13 engines depicted in canon. Early Star Wars literature and game statistics described the class as being 8,000 meters long -- the weaponry listed as average for that length if not surface area. A later correction changed that to 12,800m, strangely without changing any of the other specifications. The official Star Wars site cited it as 12,800m (as of May 29, 2005). It has since been changed to agree with the latest 19,000m specification. The earlier figure, still held by many staunch traditionalists, is in direct contradiction with the films themselves, which consistently show the Executor to be about eleven times to twelve times as long as accompanying 1,600 m long Star Destroyers or 17,600m-19,000m. Volumetric and surface-area considerations imply a much greater number of weapons than the amount earlier stated, perhaps by an order of magnitude. Similarly, these sources state there are only 144 starfighters despite having an enormous hangar bay; stills from the movie reveal that the Executors hangar bay could have easily contained an entire Star Destroyer. The approximate 19 kilometer length, the hundred-fold increase in mass from the Imperial-class, and the classification of Executor-class Star Dreadnaught is established in the Inside the Worlds of the Original Trilogy factbook, and considered canonical by Lucasfilm according to Leland Chee, LFL's "Keeper of the Holocron." It is theoretically possible to convert the older statistics to accommodate the 19,000m figure through the use of simple scaling principles. For example, older statistics say that the Executor had a crew of over 250,000 personnel. However, if the crew density were to remain the same between the 8,000 m and 19,000m versions, the crew complement would likely be in the order of 2.6 million. Nevertheless, the smaller "Super Star Destroyer" holds an allure to some of SW fandom. Part of this is due to the wide proliferation of the class. The poor combat performance of many "Super Star Destroyers" is often held as proof that the ship fighting is not an Executor, but a smaller type. For the name of this smaller type, the West End Games suggested "Super-class" is often used. This theory postulates many Super-class ships were given names confusingly similar to the much larger Executor class ships in an effort to confound Rebel intelligence. Super-class remains on the official site, despite the renovation to fit with 19,000m. The most recent sources call the Executor-class a Star Dreadnought. This clarification of nautical naming conventions is hotly disputed by a very small minority of fans, some favoring the official but colloquial "Star Destroyer" term shorn of its nautical meaning. However, technical references such as the Dorling Kindersley books, specifically Inside the Worlds of the Star Wars Trilogy canonically state this is slang. For some who find "Super-class" particularly distasteful, derivatives like "Superior" or "Superb" were often used -- both of the latter are strictly fanon. Vessels for which this rationalization is particularly common are mentioned below. Several factions continue to debate the specifications of this class of ship, and even its name. Different Expanded Universe material indicates at times the ship being a Super-class Star Destroyer (although this is generally regarded as outdated by most and mostly appears in only older source material) and at others calls it an Executor-class Star Destroyer, Executor-class Super Star Destroyer, or Executor-class Star Dreadnought (the latter designation is used by the most technically accurate sources), mostly in newer material. One recent source, Vader: The Ultimate Guide, semi-c

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