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I've been wondering lately how evolution manages to produce complex organs. It is pretty obvious to me how evolution would select some minor traits like size, resistnce to illness or climate. There is a mutation where some organisms are slightly different and better traits are selected. However I cannot imagine how an organism will mutate to have lets say lungs at once and unless organism has a functional organ there is no reason for the trait to be selected. So how does evolution produce complx organs?

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The answer is 'gradually'. All other answers will be longer ways of saying the same thing. –  Richard Smith Jul 20 '12 at 23:11
    
This is, fortunately, not true. See Evo Devo below. –  rwst Jul 21 '12 at 13:45
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It is true, there is no sudden transition from no organ to a complex organ. It happens gradually. –  Richard Smith Jul 21 '12 at 22:21
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You might find some relevant material if you search for "What use is half an eye", the classical question about how complex systems can evolve. Typically the answer is along the lines of "from smaller systems which in themselves are useful or at least not impeding". –  Armatus Aug 17 '12 at 16:46
    
@Armatus if this was an answer I would mark it as accepted. Found really simple explaination here - dbskeptic.com/2008/07/06/what-good-is-half-an-eye –  Stilgar Aug 17 '12 at 18:33
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The best introduction to evolution of complex phenotypes via master control genes is Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom by Sean B. Carroll. You might also want to have a look at a more recent Evolutional developmental biology (Evo Devo) book like those you get when searching for "Evo Devo" in Google Books.

In summary, it is possible for a mutation to change a shape by changing the spatial distribution of a transcription factor during embryo development. What's more, by changing the distribution of two mutually dependent factors, formation of any shape is possible if the distributions overlap. Such transcription factors are highly conserved in evolution and the most important cause of the endless forms we see.

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This is a strawman argument because I never stated that, either. –  rwst Jul 21 '12 at 17:52
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Just because the inverse of something is true, does not make that thing true. Organs disappearing with a single mutation is not evidence that they could ever have evolved with one. –  Richard Smith Jul 21 '12 at 22:24
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And complex phenotypes are not equivalent to organs - do you have an example of an organ which evolved as a result of a master switch? –  Richard Smith Jul 21 '12 at 22:25
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@rwst: -1, if your intention was not to state that then you have not really answered the question... You may want to quote relevant extracts from the books you refer to, in order to improve your answer. –  nico Jul 22 '12 at 9:10
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Yeah I am interested in how organs pop into existence. I am fully aware that they have been changed and improved slowly over time but unless they somewhat worked from the start evolution would not select for this trait –  Stilgar Jul 22 '12 at 12:00
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