Difference between revisions of "Evolution"
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There are three basic mechanisms of evolutionary change: [[natural selection]], [[genetic drift]], and [[gene flow]]. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is the random sampling of a generation's genes during reproduction, causing random changes in the frequency of alleles, and gene flow is the transfer of genes within and between populations. The relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the [[effective population size]], which is the number of individuals capable of breeding.[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12807795] Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.[http://www.pnas.org/cgi/content/abstract/252626899v1] As a result, changing population size can dramatically influence the course of evolution. [[Population bottleneck]]s, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population. Bottlenecks also result from alterations in gene flow such as decreased migration, [[founder effect|expansions into new habitats]], or population subdivision. | There are three basic mechanisms of evolutionary change: [[natural selection]], [[genetic drift]], and [[gene flow]]. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is the random sampling of a generation's genes during reproduction, causing random changes in the frequency of alleles, and gene flow is the transfer of genes within and between populations. The relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the [[effective population size]], which is the number of individuals capable of breeding.[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12807795] Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.[http://www.pnas.org/cgi/content/abstract/252626899v1] As a result, changing population size can dramatically influence the course of evolution. [[Population bottleneck]]s, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population. Bottlenecks also result from alterations in gene flow such as decreased migration, [[founder effect|expansions into new habitats]], or population subdivision. | ||
| − | + | ==Natural selection== | |
[[Natural selection]] is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: | [[Natural selection]] is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: | ||
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===Adaptation=== | ===Adaptation=== | ||
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Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing. They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment. This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to [[antibiotic]] selection, with mutations causing [[antibiotic resistance]] by either modifying the target of the drug, or removing the transporters that allow the drug into the cell. [http://www.jstage.jst.go.jp/article/mandi/46/6/46_391/_article/-char/en] However, many traits that appear to be simple adaptations are in fact [[exaptation]]s: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process. One example is the African lizard ''Holapsis guentheri'', which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation. | Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing. They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment. This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to [[antibiotic]] selection, with mutations causing [[antibiotic resistance]] by either modifying the target of the drug, or removing the transporters that allow the drug into the cell. [http://www.jstage.jst.go.jp/article/mandi/46/6/46_391/_article/-char/en] However, many traits that appear to be simple adaptations are in fact [[exaptation]]s: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process. One example is the African lizard ''Holapsis guentheri'', which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation. | ||
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===Co-evolution=== | ===Co-evolution=== | ||
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Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a [[pathogen]] and a [[host (biology)|host]], or a [[predator]] and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called [[co-evolution]]. An example is the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake. | Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a [[pathogen]] and a [[host (biology)|host]], or a [[predator]] and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called [[co-evolution]]. An example is the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake. | ||
===Co-operation=== | ===Co-operation=== | ||
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However, not all interactions between species involve conflict. Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[Mycorrhiza|mycorrhizal fungi]] that grow on their roots and aid the plant in absorbing nutrients from the soil. This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]]. | However, not all interactions between species involve conflict. Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[Mycorrhiza|mycorrhizal fungi]] that grow on their roots and aid the plant in absorbing nutrients from the soil. This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]]. | ||
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==Evolutionary history of life== | ==Evolutionary history of life== | ||
===Origin of life=== | ===Origin of life=== | ||
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The origin of [[life]] is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens, does not depend on understanding exactly how life began. [http://www.talkorigins.org/indexcc/CB/CB090.html] Accessed 13 May 2007. The current [[scientific consensus]] is that the complex [[biochemistry]] that makes up life came from simpler chemical reactions, but it is unclear how this occurred. [http://www.im.microbios.org/0801/0801023.pdf] Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any [[last universal ancestor|last universal common ancestor]] or ancestral gene pool. Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as [[RNA]], and the assembly of simple cells. | The origin of [[life]] is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens, does not depend on understanding exactly how life began. [http://www.talkorigins.org/indexcc/CB/CB090.html] Accessed 13 May 2007. The current [[scientific consensus]] is that the complex [[biochemistry]] that makes up life came from simpler chemical reactions, but it is unclear how this occurred. [http://www.im.microbios.org/0801/0801023.pdf] Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any [[last universal ancestor|last universal common ancestor]] or ancestral gene pool. Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as [[RNA]], and the assembly of simple cells. | ||
===Common descent=== | ===Common descent=== | ||
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All [[organisms]] on [[Earth]] are descended from a common ancestor or ancestral gene pool. Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events. The [[common descent]] of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups. | All [[organisms]] on [[Earth]] are descended from a common ancestor or ancestral gene pool. Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events. The [[common descent]] of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups. | ||
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===Evolution of life=== | ===Evolution of life=== | ||
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Despite the uncertainty on how life began, it is clear that [[prokaryote]]s were the first organisms to inhabit Earth,[http://www.journals.royalsoc.ac.uk/content/0164755512w92302/fulltext.pdf] approximately 3 - 4 billion years ago. No obvious changes in [[morphology (biology)|morphology]] or cellular organization occurred in these organisms over the next few billion years. [http://www.pnas.org/cgi/reprint/91/15/6735] | Despite the uncertainty on how life began, it is clear that [[prokaryote]]s were the first organisms to inhabit Earth,[http://www.journals.royalsoc.ac.uk/content/0164755512w92302/fulltext.pdf] approximately 3 - 4 billion years ago. No obvious changes in [[morphology (biology)|morphology]] or cellular organization occurred in these organisms over the next few billion years. [http://www.pnas.org/cgi/reprint/91/15/6735] | ||
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Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the [[Cambrian explosion]]. Here, the majority of [[phylum (biology)|types]] of modern animals evolved, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of [[oxygen]] in the [[atmosphere]] from [[photosynthesis]]. [http://www.ijdb.ehu.es/web/paper.php?doi=14756327] About 500 million years ago, [[plant]]s and [[fungus|fungi]] colonized the land, and were soon followed by [[arthropod]]s and other animals. [[Amphibian]]s first appeared around 300 million years ago, followed by early [[amniotes]], then [[mammal]]s around 200 million years ago and [[bird]]s around 100 million years ago (both from "[[reptile]]"-like lineages). However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both [[Biomass (ecology)|biomass]] and species being prokaryotes.<ref name=Schloss/> | Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the [[Cambrian explosion]]. Here, the majority of [[phylum (biology)|types]] of modern animals evolved, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of [[oxygen]] in the [[atmosphere]] from [[photosynthesis]]. [http://www.ijdb.ehu.es/web/paper.php?doi=14756327] About 500 million years ago, [[plant]]s and [[fungus|fungi]] colonized the land, and were soon followed by [[arthropod]]s and other animals. [[Amphibian]]s first appeared around 300 million years ago, followed by early [[amniotes]], then [[mammal]]s around 200 million years ago and [[bird]]s around 100 million years ago (both from "[[reptile]]"-like lineages). However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both [[Biomass (ecology)|biomass]] and species being prokaryotes.<ref name=Schloss/> | ||
| − | ==History of evolutionary thought== | + | ===History of evolutionary thought=== |
Evolutionary ideas such as [[common descent]] and the [[transmutation of species]] have existed since at least the 6th century BC, when they were expounded by the [[Greek philosophy|Greek philosopher]] [[Anaximander]]. ISBN 0-226-91038-5 Evolutionary thought was further developed by other early thinkers, including the Greek philosopher [[Empedocles]], the [[History of Western philosophy|Roman philosopher]] [[Lucretius]], the [[Islamic science|Arab biologist]] [[Al-Jahiz]], the [[Early Islamic philosophy|Persian philosopher]] [[Ibn Miskawayh]], and the [[Brethren of Purity]]. [[Muhammad Hamidullah]] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad. As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with [[Pierre Louis Maupertuis|Pierre Maupertuis]] in 1745, and with contributions from natural philosophers such as [[Erasmus Darwin]] and [[Jean-Baptiste Lamarck]].The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment, ISBN 978-0226793610. In 1858, [[Charles Darwin]] and [[Alfred Russel Wallace]] jointly proposed the theory of evolution by natural selection to the [[Linnean Society of London]] in [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|separate papers]]. Shortly after, Darwin's publication of ''[[The Origin of Species]]'' provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution. | Evolutionary ideas such as [[common descent]] and the [[transmutation of species]] have existed since at least the 6th century BC, when they were expounded by the [[Greek philosophy|Greek philosopher]] [[Anaximander]]. ISBN 0-226-91038-5 Evolutionary thought was further developed by other early thinkers, including the Greek philosopher [[Empedocles]], the [[History of Western philosophy|Roman philosopher]] [[Lucretius]], the [[Islamic science|Arab biologist]] [[Al-Jahiz]], the [[Early Islamic philosophy|Persian philosopher]] [[Ibn Miskawayh]], and the [[Brethren of Purity]]. [[Muhammad Hamidullah]] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad. As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with [[Pierre Louis Maupertuis|Pierre Maupertuis]] in 1745, and with contributions from natural philosophers such as [[Erasmus Darwin]] and [[Jean-Baptiste Lamarck]].The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment, ISBN 978-0226793610. In 1858, [[Charles Darwin]] and [[Alfred Russel Wallace]] jointly proposed the theory of evolution by natural selection to the [[Linnean Society of London]] in [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|separate papers]]. Shortly after, Darwin's publication of ''[[The Origin of Species]]'' provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution. | ||
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==Uses in technology== | ==Uses in technology== | ||
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A major technological application of the power of evolution is [[artificial selection]], which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the [[domestication]] of plants and animals. More recently, such selection has become a vital part of [[genetic engineering]], with [[selectable marker]]s such as antibiotic resistance genes being used to manipulate DNA in [[molecular biology]]. | A major technological application of the power of evolution is [[artificial selection]], which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the [[domestication]] of plants and animals. More recently, such selection has become a vital part of [[genetic engineering]], with [[selectable marker]]s such as antibiotic resistance genes being used to manipulate DNA in [[molecular biology]]. | ||
As evolution can produce highly optimized processes and networks, it has many applications in [[computer science]]. Here, simulations of evolution using [[evolutionary algorithm]]s and [[artificial life]] started with the work of Nils Aall Barricelli in the 1960s, and was extended by [[Alex Fraser (scientist)|Alex Fraser]], who published a series of papers on simulation of [[artificial selection]]. [[Artificial evolution]] became a widely recognized optimization method as a result of the work of [[Ingo Rechenberg]] in the 1960s and early 1970s, who used [[evolution strategies]] to solve complex engineering problems. [[Genetic algorithms]] in particular became popular through the writing of [[John Henry Holland|John Holland]]. Adaptation in Natural and Artificial Systems, University of Michigan Press, ISBN 0262581116 As academic interest grew, dramatic increases in the power of computers allowed practical applications. Evolution algorithms are now used to solve multi-dimensional problems more quickly than software produced by human designers, and also to optimize the design of systems. | As evolution can produce highly optimized processes and networks, it has many applications in [[computer science]]. Here, simulations of evolution using [[evolutionary algorithm]]s and [[artificial life]] started with the work of Nils Aall Barricelli in the 1960s, and was extended by [[Alex Fraser (scientist)|Alex Fraser]], who published a series of papers on simulation of [[artificial selection]]. [[Artificial evolution]] became a widely recognized optimization method as a result of the work of [[Ingo Rechenberg]] in the 1960s and early 1970s, who used [[evolution strategies]] to solve complex engineering problems. [[Genetic algorithms]] in particular became popular through the writing of [[John Henry Holland|John Holland]]. Adaptation in Natural and Artificial Systems, University of Michigan Press, ISBN 0262581116 As academic interest grew, dramatic increases in the power of computers allowed practical applications. Evolution algorithms are now used to solve multi-dimensional problems more quickly than software produced by human designers, and also to optimize the design of systems. | ||
| + | ===Michael Ruse=== | ||
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| + | There is a common belief that evolution and religion, Darwinian evolution and Christianity especially, are world pictures that are forever opposed. This is a belief today endorsed and promulgated both by extreme evangelical Christians (who support some version of Biblical literalism) and ardent ultra-Dawinians (who hold that their theory necessarily falls into an atheistic mode of thinking). Traditionally, however, this opposition has not been universally accepted. Many people find that there is much in common between the two systems and, thus, great opportunities for sympathetic dialogue. Much of the difficulty and debate arises from ignorance about the various positionsPage 280 | Top of Article involved. This is especially true of evolution. In discussing the idea of selection, it is convenient to make a three-fold distinction between the fact of evolution, the path of evolution, and the theory or mechanism of evolution. | ||
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| + | ====The fact of evolution==== | ||
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| + | The fact of evolution is simply the idea that all organisms, living and dead, came into being by a long developmental process, governed by natural laws, from organisms of a different, probably much simpler, kind. The fact of evolution includes the belief that the original organisms themselves developed by natural processes from inorganic materials. If one wanted to extend from the biological to the cosmological, one would see the fact of evolution as including all developmental change from the time of the Big Bang. | ||
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| + | Claims for the fact of evolution were first mooted in the seventeenth century with the extension of Newtonian ideas from the mere running of the universe to its supposed development through natural laws. It was later argued—by, among others, Immanuel Kant—that this happened in a regular fashion as suns and planets were formed from gaseous nebulae. Biological evolutionary ideas began to appear towards the end of the eighteenth century. A prominent exponent in England was the physician and naturalist Erasmus Darwin, grandfather of Charles Darwin; in France a little later the chief advocate of the idea was the biologist Jean Baptiste de Lamarck. | ||
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| + | The evidence offered for evolution (then more generally called transmutation) tended to be anecdotal. A major reason why few endorsed the idea with enthusiasm was that it was seen to be a reflection of the ideology of progress—upward change in the human social world, and upward change in the history of life, from "monad" to "man." Critics, like the father of comparative anatomy, the French biologist Georges Cuvier, found the idea religiously offensive less because it clashed with literal interpretations of the Bible than because of its underlying philosophy of progress. Such a world picture, in which humans can make the difference unaided, was at odds with the Christian notion of providence, where all depends on God's grace. Although by the mid nineteenth century religious worries were still much in evidence, Charles Darwin met this challenge head on in the Origin of Species (1859), the groundbreaking work in which he introduced his theory. Darwin was not the first to argue for the fact of evolution, but by marshaling so much evidence from paleontology, embryology, geographical distributions, and more, he made the fact of evolution empirically plausible and no longer reliant on an underlying social philosophy for acceptance. | ||
| + | The path of evolution | ||
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| + | The path of evolution, or phylogeny, is simply the history of the past as given in the fossil record and as can be discerned indirectly from anatomical and embryological causes and, increasingly, molecular evidence. Thanks to various sophisticated methods of dating, researchers can say that the universe itself is (since the Big Bang) about fifteen billion years old, that the Earth is about 4.5 billion years old, and that life first appeared on the planet about 3.75 billion years ago. Complex life began with the Cambrian explosion about six hundred million years ago; the Age of Mammals began about sixty-five million years ago (although the first mammals go back two hundred million years); the first known ancestors of humans are about four million years old (upright but with ape-sized brains); and, depending on how one measures things, the modern human species Homo sapiens is between five hundred thousand and a million years old. | ||
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| + | Traditionally, life is pictured as a tree with contemporary organisms at the ends of the upper branches. However, Lamarck and some other early evolutionists thought that life developed upwards in separate but parallel lines, with variations laid over these. Alternatively, some researcher believe that viruses may carry genes from one line to other, very different, lines, so perhaps a better picture is that of a net. Paradoxically, the main outlines of the history of life were worked out in the first part of the nineteenth century, primarily by those who did not subscribe to evolution, and only later was the process of life given an evolutionary interpretation. | ||
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| + | ====The theory or mechanism of evolution==== | ||
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| + | The theory or mechanism of evolution has garnered many hypotheses. Notorious before DarwinPage 281 | Top of Article was Lamarck's idea of the inheritance of acquired characteristics, which had not originated with him; Erasmus Darwin had accepted it, as did Charles Darwin much later. In the Origin of Species, Darwin described the mechanism that is generally accepted as the chief force for change: natural selection. More organisms are born than can survive and reproduce, leading to a struggle for survival and, more importantly, reproduction. Given naturally occurring variation, and the fact that those that survive will tend on average to be different from those that do not, there will be a differential reproduction, natural selection. In time this leads to full-blown evolution, and evolution of a particular kind, for selection produces organisms with adaptations. The eye and the hand come naturally as a result of Darwin's causal process. | ||
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| + | ====Conclusion==== | ||
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| + | In the years subsequent to the publication of Darwin's Origin, there have been a multitude of putative alternatives to Darwinian selection, including orthogenesis (a life force driving things), mutationism (major one-step changes), genetic drift (randomness), and molecular drive (DNA has its own built-in ways of change); none has established itself as a full and genuine rival to natural selection. This is not to say that all controversy is therefore quelled. Apart from the question of whether selection can be applied profitably to such issues as the origin of life, there are also questions about the form that life's history will take given selection as the main mechanism of change. Will it be smooth and gradual (phyletic gradualism), as supposed by Darwin and his followers, or will it be jerky and abrupt (punctuated equilibria), as supposed by some leading paleontologists, notably Stephen Jay Gould? Controversy about these issues, however, should not be taken as controversy about other matters. The fact of evolution is firmly established, the main outlines of the path of evolution have been worked out and details are being filled in (for example, that birds are descended from dinosaurs), and selection is taken to be the major mechanism of change even though there are debates about its applicability and its precise results and consequences. | ||
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| + | Evolution as fact, path, and theory is a thriving part of the biological sciences, and it is also seen to have extensions and implications for thinking about many other parts of human experience. Social scientists are increasingly turning to evolutionary ideas to flesh out their understanding of human nature and society; philosophers have (after many hesitations) begun to see how evolution, selection even, can profitably deepen their understandings of epistemology (theory of knowledge) and ethics (theory of morality); novelists and poets use evolutionary themes to illuminate aspects of human understanding and motivation; linguists turn to Darwinism for help in grasping the developments of languages; and so it is in many other subjects and disciplines. Although there is still much opposition to evolutionary ideas on various religious fronts, there is realization by theologians and historians that the old story of the warfare between science and religion was much overblown, and many see evolution as an aid to faith and understanding rather than a hindrance. | ||
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| + | ====Bibliography==== | ||
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| + | Bowler, Peter. Evolution: The History of an Idea. Berkeley: University of California Press, 1984. | ||
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| + | Depew, Daniel J., and Weber, Bruce H. Dawinism Evolving. Cambridge, Mass.: MIT Press, 1994. | ||
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| + | Desmond, Adrian, and Moore, James. Darwin: The Life of a Tormented Evolutionist. New York: Warner, 1992. | ||
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| + | Richards, Robert J. The Meaning of Evolution: The Morphological Construction and Ideological Reconstruction of Darwin's Theory. Chicago: University of Chicago Press, 1992. | ||
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| + | Ruse, Michael. Monad to Man: The Concept of Progress in Evolutionary Biology. Cambridge, Mass.: Harvard University Press, 1996. | ||
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| + | Ruse, Michael. The Darwinian Revolution: Science Red in Tooth and Claw, 2nd edition. Chicago: University of Chicago Press, 1999. | ||
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| + | Ruse, Michael. Can a Darwinian be a Christian? The Relationship Between Science and Religion. Cambridge, UK: Cambridge University Press, 2001. | ||
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| + | Ruse, Michael. Darwin and Design: Science, Philosophy, and Religion. Cambridge, Mass.: Harvard University Press, 2003. | ||
| + | |||
| + | MICHAEL RUSE | ||
| + | Source Citation: RUSE, MICHAEL. "Evolution." Encyclopedia of Science and Religion. Ed. J. Wentzel Vrede van Huyssteen. Vol. 1. New York: Macmillan Reference USA, 2003. 279-281. 2 vols. Gale Virtual Reference Library. Thomson Gale. Madison County Public. 31 Dec. 2007 | ||
| + | <http://find.galegroup.com/gvrl/infomark.do?&contentSet=EBKS&type=retrieve&tabID=T001&prodId=GVRL&docId=CX3404200183&source=gale&userGroupName=nclivemcp&version=1.0>. | ||
==Further reading== | ==Further reading== | ||
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[[Category: General Reference]] | [[Category: General Reference]] | ||
[[Category: Biology]] | [[Category: Biology]] | ||
| + | [[Category: Philosophy]] | ||
Revision as of 05:12, 31 December 2007
In biology, evolution is the change in the inherited traits of a population from generation to generation. These traits are the expression of genes that are copied and passed on to offspring during reproduction. Mutations in these genes can produce new or altered traits, resulting in heritable differences (genetic variation) between organisms. New traits can also come from transfer of genes between populations, as in migration, or between species, in horizontal gene transfer. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through natural selection or randomly through genetic drift.
Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become rarer. This occurs because organisms with advantageous traits pass on more copies of these traits to the next generation. The measurement of selection on correlated characters (Evolution, volume 37 Over many generations, adaptations occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.) [1] , Mechanisms: the processes of evolution Understanding Evolution, In contrast, genetic drift produces random changes in the frequency of traits in a population. Genetic drift arises from the element of chance involved in which individuals survive and reproduce.
One definition of a species is a group of organisms that can reproduce with one another and produce fertile offspring. However, when a species is separated into populations that are prevented from interbreeding, mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of new species. Stephen Gould, The Structure of Evolutionary Theory, Belknap Press, ISBN 0-674-00613-5 . The similarities between organisms suggest that all known species are descended from a common ancestor (or ancestral gene pool) through this process of gradual divergence. {Douglas J. Futuyma, Evolution, Sinauer Associates, Sunderland, Massachusetts, ISBN 0-87893-187-2 )
The theory of evolution by natural selection was first proposed by Charles Darwin and Alfred Russel Wallace and set out in detail in Darwin's 1859 book On the Origin of Species[2]. Related earlier ideas were acknowledged in [3] In the 1930s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis, "understanding evolution" in which the connection between the units of evolution (genes) and the mechanism of evolution (natural selection) was made. This powerful explanatory and predictive theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth. [4] Statement on the Teaching of Evolution, The Interacademy Panel on International Issues, [5] Statement on the Teaching of Evolution, American Association for the Advancement of Science.
Heredity
Inheritance in organisms occurs through discrete traits – particular characteristics of an organism. In humans, for example, eye color is an inherited characteristic, which individuals can inherit from one of their parents. (Sturm RA, Frudakis TN, Eye colour: portals into pigmentation genes and ancestry). Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype. Genetics: what is a gene? (Nature, v. 441, 2006)
The complete set of observable traits that make up the structure and behavior of an organism is called its phenotype. These traits come from the interaction of its genotype with the environment.Template:Cite journal (Epigenetics and phenotypic variation in mammals, Mamm. Genome
External links
General information
- [6] Becoming Human, The Documentary
- Understanding Evolution from University of California, Berkeley
- National Academies Evolution Resources
- Everything you wanted to know about evolution by New Scientist
- Howstuffworks.com — How Evolution Works
- Synthetic Theory Of Evolution: An Introduction to Modern Evolutionary Concepts and Theories
History of evolutionary thought
