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Natural, Relaxed, and Artificial Selection
Hasan Mahmud
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Natural Selection
• Is the basis of the other types of selection• Competition Variation• Heriatble Difference in survival
• Relaxed and Artificial Selection are simply natural selection under different
• Each of the two change different parameters and
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Relaxed Selection
• Is a selective phenomena that occurs when selective pressures are either elimated or dramatically reduced
• Are many new cases as society becomes more and more complex
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Examples of Relaxed Selection
• When selective pressures are reduced or eliminated they can be biotic or abiotic
• Biotic examples – Predation elimination – Elimination of pathogen
• Abiotic examples– Changes in light and temperature and water– Changes soil and mineral composition
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Modern Medicine
• Modern Medicine– Elimination of Many diseases that used to be
lethal– Compensation for Chronic and Genetic Diseases– Helps with common health problems• Sight problems• Hearing problems
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Other Examples
• Malaria resistance– Without the pressure of possible infection there is
no heterozygous advantage• Galapagos – Without the presence of predators
and the abundance of food many animals in the Galapagos have become much larger than their main land counterparts
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Problems with Relaxed Selection
• Many of the problems with relaxed selection only come into play when those pressures are re-introduced
• While some times the organism has come up with new way to deal with the pressures other times can be very costly to the pouplation
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Artificial Selection
• Usually through intention human involvement the selection of non-essential traits in a population
• Many times the means through which selection is done is harmful to the population
• Artificial selection is done for two purposes– To increase production such as milk, eggs, meat– Enhancement of desired traits e.x dogs horses
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Misconception of Artificial Selection
• Artificial Selection does and cannot create new traits
• Uses recessive traits or enhances existing traits to unusual expression
• Many of the artificially created species can still breed with ancestral species
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Problems with Artificial Selection
• While some examples of artificial selection are not intentional – Initial domestication of Animals– Initial enhancement of crops
• Many examples of Artificial Selection are done through in breeding – Purebred dogs– Race horses
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Connections
• Artificial, Relaxed, and Natural Selection are not separate and different forces
• Each is just a subset of the larger evolutionary force
• Artificial selection is taken to the extreme where there is a desired goal
• Relaxed selection is the absence of pressure and the evolutionary pathways that forms
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Works Cited • http://images.google.com/imghp?gbv=2&um=1&hl=en&btnG=Search+Images• 1 Bryant, Edwin H. "Fitness Decline under Relaxed Selection in Captive Populations."
Conservation Biology 13 (2001): 665-69. • 2 "Evolution and Natural Selection." Evolution and Natural Selection. 10 Oct. 2008. Universtiy of
Michigan. 5 Nov. 2008 <http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html>.
• 3 Foster, Susan A., and John A. Endler. "Effects of Relaxed Selection Evolutionary Behavior." Geographic Variation in Behavior.
• 4 Gayle, Lisa. "Genetic Disorders." Encyclopedia of Childhood and Adolescence 42 (1998).• 5 Guyon, Isabelle. "An introduction to variable and feature selection." The Journal of Machine
Learning Research 3 (2003): 1157-182. • 6 Innan, Hideki. "Pattern of polymorphism after strong artificial selection in a domestication
event." Biological Science 109 (2004): 106667-0672. • 7 "Malaria and the Red Cell." 02 Apr. 2002. Information center for sickle and thalessis Disease.
28 Nov. 2008 <http://sickle.bwh.harvard.edu/index.html>.• 8 Robertson, A. "A Theory of Limits in Artifical Selection." Proceedings of the Royal Society of
London. Series B, Biological Sciences 153 (2000): 234-49.