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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-Unna Jul 20 '12 at 23:11
This is, fortunately, not true. See Evo Devo below. – rwst Jul 21 '12 at 13:45
It is true, there is no sudden transition from no organ to a complex organ. It happens gradually. – Richard Smith-Unna Jul 21 '12 at 22:21
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
@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
up vote 4 down vote accepted

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
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-Unna Jul 21 '12 at 22:24
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-Unna Jul 21 '12 at 22:25
@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
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

It can't be explained by evolution, at least not very well. There is zero evolutionary advantage for an organism to have half of the characteristics needed for vision, in fact, multiple half formed mechanisms would be a huge detriment. That said, consider the hundreds of the complex systems present within humans? Adding time to the equation does not solve this fundamental paradox. If one of those mechanisms in a complex system does not work, the system does not work, if one of the systems in a human body does not work, it is like the person does not live (consider that of the hundreds of systems within a human body, most are essential to sustaining life). As a medical doctor I can attest to how unbelievably complex the human body is. I am not saying there is a god, but I also can't believe that time and mutation were enough to provide for the complexity we see in humans and other organisms.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

Could you add citations to your assertions? – kmm Sep 3 '15 at 0:33
Though he is somewhat smug and arrogant, I think Richard Dawkins has answered many of the questions you can't seem to explain in popular lectures that you can view on the web. You can also read his books, maybe pick up a textbook on Evolution. Evolutionary changes are on a continuum, they don't happen it discrete steps but happen in small and imperceptible changes that get passed down over many generations. Minute variations in each generation over hundreds to thousands of generations can lead to changes that when compared in discrete steps appears like an impossible jump. – AMR Sep 3 '15 at 3:48
Genetic homology also provides significant evidence to support evolution and common ancestry. Recombinant DNA technology has shown us that our DNA can be copied just as well in the cells of a mouse or in bacteria as it can in our own cells. We have a sustainable supply of human insulin because E.coli can translate our insulin gene into a fully functional protein that works to control our blood sugar, just as if it had been produced in our own pancreas. And what is gestational development if not the evolutionary program executed over a very short period of time? – AMR Sep 3 '15 at 3:55
If we start from the fusion of two gametes, then at early stages of development that amazing eye is just a collection of light sensitive cells without an iris, cornea, lens, etc. basically is the proto-eye that our evolutionary ancestors survived with. As genes changed and better vision provided selective advantage, then those steps were preserved through evolution until we get to the eye we have today, which isn't so great when you compare it to that of raptors, or nocturnal animals, or animals that can see in a wider spectrum than we can. – AMR Sep 3 '15 at 4:00
We even start out with a notochord at the early stages of development, which as the evolutionary program is carried out during gestational development becomes the discs between the vertebrae. As our common ancestors evolved beyond simple vertebrates, they developed small incremental changes that eventually extended the CNS into a spinal cord. – AMR Sep 3 '15 at 4:06

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