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Natural selection


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darwin's theory of natural selection

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Natural selection

  2. 2. ContentsContents  Introduction  Factor of Darwinism  Rapid multiplication  Limited environmental resources  Struggle for existence  Variation  Survival of the fittest  Inheritance of the useful variation  Formation of new species  Darwinism V/S Lamarckism  References 11th July, 2015 2
  3. 3. IntroductionIntroduction  Darwinism : Darwin's Theory of Natural Selection.  The theory of the evolution of species by natural selection advanced by Charles Darwin announced on July 1, 1858.  Darwin travelled round the world in the 19th century on the ship H.M.S. Beagle with a surveying expedition for 5 years (1831-1836).  “On the origin of species by Means of Natural Selection “, November,1859. 311th July, 2015
  4. 4. Natural SelectionNatural Selection  Darwin’s most famous and most important theory of evolution.  Only process that promotes adaptation.  The machenism for adaptation and evolution is called “natural selection”  This theory states that “ Those organisms best adapted to their environment have a better chance of surviving and reproducing.” 411th July, 2015
  5. 5. Factor of DarwinismFactor of Darwinism • Rapid multiplication • Limited environmental resources • Struggle for existence • Variation • Survival of the fittest • Inheritance of the useful variation • Formation of new species 511th July, 2015
  6. 6. 1. Rapid multiplication (over production)1. Rapid multiplication (over production) Organism reproduce more offspring than can survive. There is high death rate. e.g. -  Paramecium divide 3 times in 48 hours with this rate, a single paramecium will produce in 5 year a mass of paramecium equal to ten thousand times the size of earth.  Plant produce thousands of seed each year.  cod fish may produce over a million egg in a year. If all the egg developed into fishes, the whole Atlantic Ocean will be full of cods in Five years. 611th July, 2015 Source:
  7. 7. 2. Limited environmental resources (space & food)2. Limited environmental resources (space & food) • Increase of population in animal & plants requires more space and food but the universe remains constant. • Individuals compete for limited resources • food, • water, • spaces, • mates. 11th July, 2015 7
  8. 8. 3. Struggle for existence (competition)3. Struggle for existence (competition) Competition among members of a species for food, living space, and other necessities of life. The Struggle for existence is 3 fold for every individual :- • Intraspecific struggle  Within species • Interspecific struggle  Different species • Environmental struggle  Change in environmental factor (heat, cold, drought, flood, famine etc..) 811th July, 2015 Source1 : Source2 : Source3 :
  9. 9. 4. Variation & Adaptation4. Variation & Adaptation • Understanding how individuals of the same species vary was key to Darwin developing his theory. • Because the environment changes, the more variation within a species, the more likely it will survive. • Each individual has a unique combination of inherited traits. • An inherited traits that increase an organism's change of survival is called “Adaptation”. Fig : the original species of the finch had a small beak where it only was able to eat insects and nectar. As centuries pasted the finch's beak started to curve downward making the advantage for the bird to tears bark from trees. However, current finches are nectar feeders who look closely to a iiwi and that their beaks are long and curved downward suggest that Darwin's theory of natural selection made the finches advantage being able to get nectar from bark and and flowers. 911th July, 2015 Source :
  10. 10. 5. Survival of fittest (natural selection)5. Survival of fittest (natural selection) • The individuals with the best traits / adaptations will survive and have the opportunity to pass on it’s traits to offspring. • Natural selection acts on the phenotype (physical appearance), not the genotype (genetic makeup). Fig : some Giraffes have long neck and other have short neck. Something caused low-lying shrub to die out, the giraffes with short neck would not get enough food. After a few generation all the giraffes would have long necks. 11th July, 2015 10 source: 65d39ace9c79f28/tekamul-07.jpg
  11. 11. 6. Inheritance of the useful variation6. Inheritance of the useful variation • The individual, selected by nature, pass on their useful variation to the next generation. • Thus, offspring of fit individual also be fit. 11th July, 2015 11 6. Inheritance of the useful variation6. Inheritance of the useful variation Source
  12. 12. 7.7. Formation of new speciesFormation of new species • In each generation, new favorable variations appear and supplement the favorable. • After a number of generation the variations become so many which generate a new specie 11th July, 2015 12 Fig : the Origin of Species source :
  13. 13. Darwinism v/s LamarckismDarwinism v/s Lamarckism 1. It doesn’t believe in the internal vital force. 2. These vital force do not form part of Darwin’s natural selection. 3. An organ can develop further or degeneration only due to continuous variation 4. Struggle for existence is vary important. 5. Only useful variation are transferred to next generation. 6. Darwin’s natural selection theory is based on survival of the fittest. 1. There is an internal vital force in all organism. 2. It consider new need or desire or produce new structure & change habits of the organism. 3. According to this theory if organ is contently used it would be better developed where as disuse of organ results in its degeneration. 4. No concept of struggle for existence 5. All the acquired characters are inherited to the next generation . 6. Lamarckism does not believe in survival of the fittest. 11th July, 2015 13
  14. 14. ReferencesReferences   Biology, Textbook class XII (NCERT)  Pradeep's A Text Book Of Biology class 12th ; G. Chopra, H.N. Srivastava, P.S. Dhami.  Selection.aspx  option=com_content&view=article&id=36&Itemid=123  change/  10239059 11th July, 2015 14
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