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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?

Stilgar
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    The answer is 'gradually'. All other answers will be longer ways of saying the same thing. – Rik Smith-Unna Jul 20 '12 at 23:11
  • This is, fortunately, not true. See Evo Devo below. – R Stephan 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. – Rik Smith-Unna 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 - http://www.dbskeptic.com/2008/07/06/what-good-is-half-an-eye/ – Stilgar Aug 17 '12 at 18:33
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    @Stilgar: Nice article, though I think it's worth mentioning that the human eye has not evolved from this line ;) The mammalian eye develops as an outgrowth of the brain whereas the given examples all develop first and then attach to the brain (according to biology year 12 which may have been wrong of course) – Armatus Aug 17 '12 at 19:18
  • Still it make sense to me (as total Biology noob). First some tissue forms that works in some very basic way and then it evolves to form an organ. – Stilgar Aug 17 '12 at 19:54
  • Watch The Christmas Lectures by Richard Dawkins, here https://www.youtube.com/playlist?list=PL24C9639BE2DD4223 In one of them he shows how an eye can evolve incrementally. You don't need much biological training or knowledge to appreciate them. – AMR Sep 04 '15 at 03:20
  • you may be interested in cloacal breathing in turtles and things called swim bladders. both are ways incomplete lungs can be useful. There is no such thing as an irreducibly complex organ. – John Apr 13 '20 at 04:24

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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.

R Stephan
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  • Excuse my ignorance but I have only studied high school biology 15 years ago and in another language. If I understand your answer correctly it is possible for a mutation to create a functional organ at once? – Stilgar Jul 21 '12 at 14:13
  • No. You said above there are always small steps, and I said this is not true. The shape of an organ, when it is already evolved, can change drastically because it is determined by processes that are very sensible to the environment and to some mutations. – R Stephan Jul 21 '12 at 14:31
  • PS. There are indeed mutations that can 'create' a functional organ at once, because there are mutations that can make organs disappear. Just do the reverse change. I know the reverse would be near impossible in evolution. – R Stephan Jul 21 '12 at 14:36
  • This is a bit too simplistic. For sure we did not get from unicellular organisms to organisms with a stomach, hearth and lunghs just with a couple of mutations. Several small adaptive steps exist in the middle. – nico Jul 21 '12 at 15:31
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    This is a strawman argument because I never stated that, either. – R Stephan 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. – Rik Smith-Unna 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? – Rik Smith-Unna 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 09:10
  • Part of organ complexity is shape, and that can well be changed with a single mutation or even small change in environment. The question isn't about lungs popping into existence. It's about lungs with all their complexity, and part of that can change drastically. As you're not inclined to accept anything from me, I will close this now – R Stephan Jul 22 '12 at 10:07
  • @rwst: I am very sorry that you are taking this so personally. The only thing I am interesting into is to have a good answer, I don't care who writes the answer. The OP states: I cannot imagine how an organism will mutate to have lets [sic] say lungs at once so it is clear that he is asking for how lungs popped into existence, not how they were modified from a previous existing respiratory apparatus. – nico Jul 22 '12 at 11:02
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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
  • @rwst it's not a personal attack, it's just that the interesting point you've made (that complex phenotypes can appear rapidly in evolution due to master switches) does not demonstrate that organs arise suddenly, but that they can change form quite suddenly. It doesn't answer the question. It remains that gradual accumulation of small changes still accounts for evolution of the molecular networks which might be rearranged by a master switch mutation. For what it's worth, I do think your answer was interesting :). Please don't stop contributing just because of this. – Rik Smith-Unna Jul 23 '12 at 14:18
  • -1 While certainly relevant, I don't think this answer is actually answering the question. Will undo if improved of course :) – Armatus Aug 17 '12 at 16:47