Yahoo Answer again too long

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http://answers.yahoo.com/question/index;_ylt=AoE1f2trPibL5RP1meAEbJ4jzKIX;_ylv=3?qid=20090124121806AANmIjB

"Is evolution a scientific theory ?


For a theory to be scientific it has to have repeatable experiments with a predicatable outcome. Evolution ( macro evolution ) is not repeatable as far as i know, so why do scientists then say that evolution is a scientific theory ? when they can not repeat an experiment where for instance a fish transforms into a bird ?



Honest answers only please.

Additional Details

3 days ago



i am aware of the fruit flies experiments. yet these are small changed ( micro evolution ), for macroevolution i do not know any repeatable experiments.



i strongly believe that experiments has to be repeatable , if not there is no point of makeing a theory out of it, since theories are used to predict the futur. it doesnt make sense to get rid of the "non repeatable experiments constraint" in a theory if it are only one time events ."
 
My Answer:

Evolution can't make predictions about how things will change only that things will change. Also evolution doesn't say that any species changes into another species, every succeeding generation is going to be a more specific representative of its current species. Over time differentiation of lineages from one ancestral population will result in the ancestral species being referred to as a genus.




No one would be able to induce a fish to evolve into a bird, in nature the pathways of evolution from fully aquatic fish, to tetrapod fish, to amphibious tetrapod, to full amphibian, to reptile, to therapod dinosaur, to bird took hundreds of millions of years. No laboratory has the time to repeat that. We also don't have the facilities to reproduce every environmental condition that might have served as timely selective pressures for specific changes, and we have no control over how genes will mutate. If we were to take the earth back in time 500 million years or so and let it play out again evolution most likely wouldn't progress along the same lines it has in our observable universe specifically because of certain completely random elements in gene mutation, specifically the effects of beta decay on DNA.



This doesn't mean, however, that we can't perform laboratory experiments that show us the process of evolution at work. If we understand that evolution works through inhertance and variability, natural selection and sexual selection, and genetic drift and reproductive isolation, then we only need show each part actually occurs in nature and the theory is confirmed if you can show these parts also are linked.



No one doubts that each generation inherits traits from its parents. This is a well established fact, so we can consider inheritability proven. Mutations are often wrongly disputed by creationists, though. In reality many beneficial mutations have been well documented and even reproduced in larboratories.



http://en.wikipedia.org/wiki/Nylon-eating_bacteria

http://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment#Results

http://en.wikipedia.org/wiki/Radiotrophic_fungus



Those are just three examples of many. These mutations added information to their respective genomes and were beneficial. They improved reproductive fitness and thus were more successful at being passed on to future generations. It's also interesting to note that all three of these mutations don't deal with enhanced survival through resistance to something that might harm them, but through the adaptation of a new pathway for metabolizing something found in their environments. Nylonase evolved a pathway for metabolizing the waste products of industrial nylon production, one of the e. coli colonies in the long term e.coli evolution experiment evolved a way to metabolize citrate which e. coli normally just cannot do at all. And the fungus evolved the ability to turn radiation into a source of energy similar to the way plants use sunlight.
 
From those experiments I think we can consider the fact that beneficial mutations occur to be an established fact. Well that and the fact that we can look at the genomes of the ancestral populations of all of these species and see that these genes just aren't there.




Natural and sexual selection deal with how selective pressures will help to determine what mutations including but not limited to mutations that render individual organisms unviable improve or harm or have no effect on reproductive fitness. Mutations that don't actually harm viability but which provide some other disadvantage due to environmental considerations are culled either because the individual is less likely to survival to reproduce or because the individual is not appealing to potential mates. This was demonstrated to work from the famous peppered moth experiments which many creationists wrongly attempt to discredit on completely irrelevant grounds. The color of the moths had no direct effect on the individual moth's viability, but in areas with lighter bark on the trees the black moth's pigment was a liability for them since it made them stand out to predators, while in sooty areas with darker bark on the trees the light colored moth's pigment was the liability. From this experiment and many others like it we can clearly see that natural selection is a force that really does operate in nature, and by observing bird populations esspecially we can clearly see sexual selection at work in plumage and coloration. From these facts I think it is safe to say that natural and sexual selection are real phenomena.



Now taking these facts into account we move on to reproductive isolation and genetic drift. These two aspects are completely logical, we can confirm them with a simple thought experiment. Whether or not you are satisfied with the evidence in favor of mutations or natural and sexual selection, let's just accept them as true for the sake of argument. Now evolution deals with gene pools within populations, not with individuals. With these assumptions just granted for the sake of argument (though I think I provided good evidence in favor of them all), it follows that within a given population if mutations happen and inheritance is always passed on from parents to offspring, that genetic drift will happen concerning which mutations make it into the general population and are inherited by all members of succeeding generations. This follows directly from how inheritance works. Evolution is a mathematical model known as a markov chain.



http://en.wikipedia.org/wiki/Markov_chain



This basically means that it's the current state that determines how the next state will evolve and not any of the states before. This follows from the fact that we don't get our genes directly from our grand parents or great grandparents and so on, each individual will only inherit the genes that are present within their parent's genomes and mutate new traits from that limited pool. Because of this some genes can be lost from any given gene pool. Markov Chains are a statistical model and thus are subject to the law of large numbers. So in large populations the tendancy will be for there to be, for the most part, a sort of statis until or unless an adaptation is evolved into the gene pool that makes a very significant change in reproductive fitness, or something dramatic happens to the environment.



Reproductive isolation, however, is when a small subset of a species general population becomes isolated and no longer shares genes with the larger gene pool. In a smaller population genetic drift is more inclined to favor new mutations no matter how innocuous, but esspecially if they improve reproductive fitness even just a little bit. Over time, if two lineages of the same population never mix genes they will accumulate, through the inevitable random mutations, enough differences in their gene pools that they become noticeably distinct. Unless you can think of a reason why they shouldn't when we've granted the assumption that mutations happen. Keep in mind, though, that reproductive isolation doesn't mean the two populations can't mix for any biological reason, they could still interbreed if they could get together, but the isolation could be geologically imposed, or it could be ecologically imposed. It could even be imposed by bias in the whole sexual selection process (Like some birds preferring mates with lots of red feathers and others preferring mates with lots of green feathers).



So you see if we just prove that mutations happen and can be beneficial and that natural and sexual selection are real processes in nature, the rest follows logically. I leave inheritance out because I don't know anyone at all who disputes inheritability. The evidence from genetics, phylogenetics, the fossil record, etc, is just icing on the cake.