animals developing limbs?

Okay, I have always wondered something about evolution. How is it possible through natural selection for the amphibians and other species that grew limbs and crawled out of the water to become land animals to have done so? It just doesn't make sense. In natural selection an organism will have a new trait that is advantageous, and then reproduce and more will have that trait, and then the one's that do not have the trait will die off, and then that species has evolved. It makes sense for speed and strength, but not for the growth of limbs...especially since it took place over millions of years, the first little change would be a small stub at the very least, and that would not help the animal at all, much less cause it to evolve further...Can anybody answer this?

Thread moved here from the Proposed New Topics forum.

The original advantage of "small stubs" that could have developed into fins may have been their sensory role, rather than for locomotion. Think about it, and it's a role our limbs still have, and if you close your eyes, perhaps you can imagine how small sensory appendages could have been advantageous to a small blob of a blind proto-fish.Any mutations that enabled the appendages to help the organism swim would then be an advantage.Here's a paper from about 10 years ago that gives you an idea of how biologists are looking for and finding genetic clues which should one day fully answer that question in detail.Just a moment...As for your first question: That's easier to explain, and there are fossils of fish with leg like fins. Being able to use your fins as legs could be advantageous in certain circumstances. You can anchor yourself against a current, rather than spending energy swimming against it, and you can move where it's too shallow to swim.Some modern fish use the strategy, and this little fellow is my favourite.http://www.arkive.org/...s/GES/fish/Brachionichthys_hirsutusCute, eh? That's convergent evolution, but here's a well known ancestor, or close ancestor relative of ours.Tiktaalik roseae: HomeSay hi to your great grandaddy, and welcome to EvC.

I am talking about a stub that can not even be seen to the naked eye. Correct me if I am wrong, but if it takes millions of years for a limb to develop, then the first change would be nearly microscopic. I can understand a 1 inch protrusion being advantageous, but it would never be that big. Or is the first change the most dramatic?Edited by metalpwner, : No reason given.

Genes control development, and a single mutation could produce symmetrical appendages large enough to be useful to the creature. Don't make the mistake of thinking that it takes a mutation to create an extra cell!See what various single mutations can do, for example, here:Polydactyly - WikipediaYou can get an extra digit on each limb plus other characteristics just from one mutation. Most of these are disadvantageous. However, some just give the extra digit, and the equivalent of that in the past might have moved our ancestors from 4 to 5 digits, turned out to be advantageous, and stuck (became fixed in our species). From the article, note:

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The extra digit is usually a small piece of soft tissue; occasionally it may contain bone without joints; rarely it may be a complete, functioning digit.

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It's as if nature is constantly experimenting, but because of the randomness of the mutations, most of the experiments are either neutral or disadvantageous to the individual organism.If you go back to our speculative proto-fish, thousands of individuals could have received useless mutations producing useless appendages before one got the first useful limbs, and they only have to be slightly useful.Any characteristic that makes an individual slightly more likely to survive to adulthood and produce offspring will tend to spread across the whole population group over time (it could be hundreds of generations) and become a fixed characteristic of the species. Actually, the pre-appendage blob we're talking about was probably very small, so it wouldn't need one inch appendages. But no, the first stage doesn't have to be that dramatic, and the advantage, as I said, need only be slight.Purely neutral characteristics can spread across a group by sheer chance (genetic drift) so anything slightly better than neutral goes.

A single mutation can give someone a fully working appendage. How many people do you see with a fully working 6th finger? I believe you are wrong, it takes a human fetus roughly 5 months to develop all its limbs. You are conceptualizing it wrong. You are thinking that one generation grows a tiny stump, then generation after generation the stump grows larger untill finally, millions of years later, it is fully functional having all the while just been a nusance for the species to have this stump untill it developed. This is incorrect. That is not the way mutations work, it is not the way evolution works. Like I said before a single mutation can render a fully functional appendage, if it is advantagous as bluegenes stated, then it is beneficial for survival and may get passed on. However, it could pop in and out, like in my examplae of a 6th finger, never really benefiting in anyway.

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All great truths begin as blasphemiesI smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your fuckin' mouth.

Hello metalpwner. Because they didn't. They adapted existing limbs -- fins -- so that they provided the strength and support necessary to walk on land. The bones and muscles were already there for the fins. Read about Tiktaalik:Tiktaalik roseae: Home You have it half right: if the new trait does not interfere with existing ability to survive and breed it will spread in the population. And yet even single cell life have 'limbs' -- from flagella to pseudopods, and these rudimentary limbs have a survival advantage. Nothing "causes" evolution to occur one way or the other, and there is no "further" direction. Life is continually evolving, and when there are opportunities for new traits to provide an advantage to breed or survive they will be passed on.You may also want to look at some websites that provide some good information on evolution:An introduction to evolution - Understanding EvolutionIs by the Berkeley University Biology Dept and is designed as a teachers and student aid.Enjoy.ps - as you are new here, some tips:type [qs]quotes are easy[/qs] and it becomes: or type [quote]quotes are easy[/quote] and it becomes:

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