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I read a lot about speciation. To my knowledge, a species is often defined as a group of individuals that actually or potentially interbreed in nature and produce fertile offspring. Speciation is a lineage-splitting event that produces two or more separate species.

Now, some creationists claim that there is no speciation, rather variation in the same species. As in "fruit fly experiment", I read that two groups of fruit flies don't interbreed after the evolution and speciation takes place. As per the definition of species (biological concept of species), they are supposed to be two separate species (reproductive isolation). Nevertheless, creationist claim they are still fruit flies and there is no speciation. They say that's just a variation in fruit flies, not speciation. I can't understand their claim.

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    $\begingroup$ Voting to close because this is a question of semantics. You both observe the same phenomenon and are arguing over which word to describe it. Whether you call it speciation or variation, the event still happened. $\endgroup$
    – canadianer
    Jul 26, 2015 at 7:02
  • $\begingroup$ you should probably go to reddit with this question - they are more focused on handling such questions and dealing with the interface of the general public with science there. $\endgroup$
    – shigeta
    Jul 26, 2015 at 16:07
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    $\begingroup$ @canadianer variation and speciation have different meanings. Tanvir, you should clarify where you have actually seen this usage; it would be easy for us to check the authenticity of the reference. Basically, variation is a general term to describe genetic and phenotypic variability whereas speciation, as you have indicated, has additional constraints. $\endgroup$
    – WYSIWYG
    Jul 27, 2015 at 5:01
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    $\begingroup$ @WYSIWYG Even after re-reading the question, I can't quite remember what point I was trying to make, but you've certainly missed it ;) $\endgroup$
    – canadianer
    Jul 27, 2015 at 5:33

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You are asking explanations about a creationist argument. One could provide explanations about some hypothesis that you may found in a science paper but not explanations for a creationist argument just because, by definition, a creationist argument is not supported by any evidence and logical thoughts. However, you may want to link to a creationist website making a specific claim of interest and we may eventually talk about whether the claim is wrong/misleading. It would be very handy to have the claim in quotes rather than an explanation of what the claim is.

You say

[..] after the evolution and speciation [..]

This piece of sentence sounds weird. You could say after the evolution of something (meaning the appearance of this something through evolutionary processes that are mutations, natural selection, drift and eventually others) but just "after the evolution" sounds as if evolution may not exist during some periods of time.

Talking about speciation in fruit flies, you will likely be interested in reading this post.

UPDATE

In general, when talking about fruit flies we talk about the Tephriditae. Tephriditae is a family of flies which contain about 5000 described species (including the model organism Drosophila melanogaster).

So, there is definitely different species of fruit flies. Of course, within any population (to the exception of populations of exact clones by definition), you have variation. This variation is a key concept in evolutionary biology. If this is unclear to you you may want to learn a bit more about evolutionary biology, including the concept of heritability ($h_N=\frac{V_A}{V_P}$).

Speciation took place in Tephriditae (otherwise we wouldn't have the species we have today) and is still taking place. The post I linked above gives an example of speciation between lineages of Drosophila melanogaster that has been directly observed in the labs.

Your issue seems to likely be a semantic one. As there is variation within a lineage and this variation is associated with groups that are in reproductive isolation, then the two lineages you consider do not belong to the same species anymore. Therefore, there was a speciation event.

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  • $\begingroup$ Actually, I do belive in evolution and I m an atheist. When I raised the fruit flies case to a creationist , he said, they are still fruit flies and there is no speciation. He said thats just a VARIATION in fruit flies, not speciation. But I cant find any logic there. IS IT SO ? He alwasy links VARIATION to SPECIATION case. HE says there is never SPECIATION taking place, its just a VARIATION in the same species. $\endgroup$
    – Tanivr
    Jul 26, 2015 at 6:44
  • $\begingroup$ I added an UPDATE to my answer. Let me know if this answers your question. $\endgroup$
    – Remi.b
    Jul 26, 2015 at 7:02
  • $\begingroup$ Thnk u very much. I m grateful. I got the same understanding as u mentioned. But I think creationists dont know the meaning of species. One more thing, he said, he doesnt want to talk about insects in this context, since it creates some problems , such as- 1.Anachronism 2. Grandfather Paradox . What are they, How on earth are they related to speciation ? $\endgroup$
    – Tanivr
    Jul 26, 2015 at 7:39
  • $\begingroup$ I never heard of the concept of anachronism in evolutionary biology and the grandfather paradox is related to time travel, so it definitely has nothing to do with evolutionary biology. $\endgroup$
    – Remi.b
    Jul 26, 2015 at 7:49
  • $\begingroup$ He said- The slow changes in traits in organisms taking tens of thousands of years to yield a visible change in variation as you suggest, does eventually trap yourself in to a problem of "Time Riddle" - you just dont have enormous enough of time at hand for all these species to come into being. A quick average time calculation suggests that you should have a new species come into being every 15-20 yrs [just rough average time estimation suggests that in about 1 billion yrs ~50 million distinct species evolved]. Don't just start with punctured equilibrium now. You just cannot have it both ways. $\endgroup$
    – Tanivr
    Jul 30, 2015 at 7:03

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