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I had a debate with a person who believes in some kind of creativism, let's call it that way.

And in the middle of the "debate", an interesting question popped up.

What are evidences of "transition between species". Is there a fossil record that shows us the "transition". I googled it and it was pretty obscure subject.

I would like to answer that question and really it "hits" my beliefs.

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    $\begingroup$ As it is, this reads like you are asking whether there is any fossil record at all for evolution between species, which I am pretty sure is not what you want to know. Can you clarify what you mean some more? What evidence would you accept? What transition are you looking for? $\endgroup$
    – YviDe
    Commented Jan 31, 2016 at 18:13
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    $\begingroup$ Speciation is a gradual and continuous process. A new species does not pop up in just one generation. It takes many. This, combined with the highly incomplete fossil record makes that transitions between two species are likely to be difficult to document. As YviDe asks - what are you after? $\endgroup$
    – AliceD
    Commented Jan 31, 2016 at 18:47
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    $\begingroup$ Also, what search term did you use to conclude that it is an "obscure" subject? The search for "transition fossil" or "transition species" gets a lot of good hits on the subject. $\endgroup$
    – YviDe
    Commented Jan 31, 2016 at 18:47
  • $\begingroup$ Welcome to Biology.SE. There are millions of evidence in evolutionary biology. You can find a long list of evidences on this post. However, the question is a little unclear for the moment and I don't really know which evidence would answer your question. I am voting to close as unclear. $\endgroup$
    – Remi.b
    Commented Jan 31, 2016 at 19:24
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    $\begingroup$ Could you clarify what you mean by transition between species $\endgroup$
    – rg255
    Commented Jan 31, 2016 at 21:40

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People who think in creationism or think about species rigidly might have a bit problem with that, so let me describe an example:

When are humans "adult"? Legally, at 18 (or your national equivalent). However, everyone understand that people are becoming adult gradually. Sometimes, they "age" very quickly after some harsh experience (16 years old student who parties all days because parents pay for it vs 16 years someone whom father died and he has work to help feed his small sisters as family did depend on father's wage).

Now imagine that you don't have all this information, but very incomplete "images" or "screenshots" of this kind of development. There would be quite a mess from it. You have image of one kid at 13 who is still young, another kid at 19 who is partying, single image of this 16 year old adult who has to feed his family and image of 48 year old gentleman.

If you go with this mindset that most of species that ever lived you can't get and you are just guessing something from a few snapshots that are themselves incomplete as well (e.g. we often don't have whole skeleton but just single bone from a lot of species), your idea on what to expect will change. This is a first step. Then you need to realize that most of fossils that shows some transition do not form lineage, but instead branches that are related. Finally, when you understand this (and modify your expectations and "what to look at", you can take any relatively complete and well-studied set of fossils like human ones. On human lineage (with great apes), we can see gradual increase of brain and in the case of human, gradual decrease in size of jaw. Development of hip bone is nice as well as it shows gradual process of adaptation to upright walking.

Another line of examples, but again, you need to redefine your expectations, is to point on dogs. If we had dogs in our fossil records, there would be large amount of species, instead of one "dog" species.

Or you can just point out at plants and say that "species" does not really mean anything.

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  • $\begingroup$ I appreciate the analogy with adult age to explain why the question makes little sense. $\endgroup$
    – Remi.b
    Commented Jan 31, 2016 at 21:54
  • $\begingroup$ @Remi.b: I don't think it's nonsensical question per se. Rather, you really need to know what you are looking for unless you will miss the elephant in the room. Furthermore, these "transitional states" show nicely how some systems have developed. Currently, I am working on some anthropological/sociological stuff and if you find these "transitional states", you might understand how particular cultural motive or practice did develop and reconstruct the actual process. $\endgroup$
    – Colombo
    Commented Feb 1, 2016 at 1:33

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