he Antikythera mechanism (pronounced /ˌæntɨkɨˈθɪərə/ ANT-i-ki-THEER-ə or pronounced /ˌæntɨˈkɪθərə/ ANT-i-KITH-ə-rə) is an ancient mechanical computer[1][2] designed to calculate astronomical positions. It was recovered in 1900–01 from the Antikythera wreck.[3] Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100 BCE.[4] The degree of mechanical sophistication is comparable to a 19th century Swiss clock.[5] Technological artifacts of similar complexity and workmanship did not reappear until the 14th century, when mechanical astronomical clocks were built in Europe.[6]
Jacques-Yves Cousteau visited the wreck for the last time in 1978,[7] but found no additional remains of the Antikythera mechanism. Professor Michael Edmunds of Cardiff University who led the most recent study of the mechanism said: "This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely carefully ... in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa."[8][9]
The device is displayed at the National Archaeological Museum of Athens, accompanied by a reconstruction made and donated to the museum by Derek de Solla Price. Other reconstructions are on display at the American Computer Museum in Bozeman, Montana, the Computer History Museum in Mountain View, California, the Children's Museum of Manhattan in New York, and in Kassel, Germany.
Friday 29 April 2011
Friday 22 April 2011
EVOLUTION
Evolution (also known as biological or organic evolution) is the change over time in one or more inherited traits found in populations of organisms.[1] Inherited traits are particular distinguishing characteristics, including anatomical, biochemical or behavioural characteristics, that are passed on from one generation to the next. Phenotypic expressions of these traits can be influenced by gene–environment interactions. Evolution may occur when there is variation of inherited traits within a population. The major sources of such variation are mutation, genetic recombination and gene flow.[2][3][4][5] Evolution has led to the diversification of all living organisms, which are described by Charles Darwin as "endless forms most beautiful and most wonderful".[6]
Two processes are generally distinguished as common causes of evolution. One is natural selection, a process in which there is differential survival and/or reproduction of organisms that differ in one or more inherited traits.[1] Another cause is genetic drift, a process in which there are random changes to the proportions of two or more inherited traits within a population.[7][8]
In speciation, a single ancestral species splits into two or more different species. Speciation is visible in anatomical, genetic and other similarities between groups of organisms, geographical distribution of related species, the fossil record and the recorded genetic changes in living organisms over many generations. Speciation stretches back over 3.5 billion years during which life has existed on earth.[9][10][11][12] It is thought to occur in multiple ways such as slowly, steadily and gradually over time or rapidly from one long static state to another.
The scientific study of evolution began in the mid-nineteenth century, when research into the fossil record and the diversity of living organisms convinced most scientists that species evolve.[13] The mechanism driving these changes remained unclear until the theory of natural selection was independently proposed by Charles Darwin and Alfred Wallace in 1858. In the early 20th century, Darwinian theories of evolution were combined with genetics, palaeontology, and systematics, which culminated into a union of ideas known as the modern evolutionary synthesis.[14] The synthesis became a major principle of biology as it provided a coherent and unifying explanation for the history and diversity of life on Earth.[15][16][17]
Evolution is currently applied and studied in various areas within biology such as conservation biology, developmental biology, ecology, physiology, paleontology and medicine. Moreover, it has also made an impact on traditionally non-biological disciplines such as agriculture, anthropology, philosophy and psychology.
Two processes are generally distinguished as common causes of evolution. One is natural selection, a process in which there is differential survival and/or reproduction of organisms that differ in one or more inherited traits.[1] Another cause is genetic drift, a process in which there are random changes to the proportions of two or more inherited traits within a population.[7][8]
In speciation, a single ancestral species splits into two or more different species. Speciation is visible in anatomical, genetic and other similarities between groups of organisms, geographical distribution of related species, the fossil record and the recorded genetic changes in living organisms over many generations. Speciation stretches back over 3.5 billion years during which life has existed on earth.[9][10][11][12] It is thought to occur in multiple ways such as slowly, steadily and gradually over time or rapidly from one long static state to another.
The scientific study of evolution began in the mid-nineteenth century, when research into the fossil record and the diversity of living organisms convinced most scientists that species evolve.[13] The mechanism driving these changes remained unclear until the theory of natural selection was independently proposed by Charles Darwin and Alfred Wallace in 1858. In the early 20th century, Darwinian theories of evolution were combined with genetics, palaeontology, and systematics, which culminated into a union of ideas known as the modern evolutionary synthesis.[14] The synthesis became a major principle of biology as it provided a coherent and unifying explanation for the history and diversity of life on Earth.[15][16][17]
Evolution is currently applied and studied in various areas within biology such as conservation biology, developmental biology, ecology, physiology, paleontology and medicine. Moreover, it has also made an impact on traditionally non-biological disciplines such as agriculture, anthropology, philosophy and psychology.
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