Alright Andy, it seems we need to have a discussion. Can you lower your defenses and chill with the offense and let's just talk. You up for that?
I'm not talking about evolution within species'
There is no magical dividing line between speciation and common ancestry. In fact it is because of speciation that populatons wind up with common ancestors. Also, just because I have a feeling it might be an issue going forward - descendants never stop being what their ancestors were. So apes and Old World Monkeys never stop being Catarrhines. Catarrhines never stop being Simiformes (all apes and monkeys). Simiformes never stop being Primates and never stop being Euarchontoglires, etc. etc.
I'm talking about all that nonsense of fish becoming mammals.....
So here we go. There is a long evolutionary history through terrestrial tetrapods to Synapsids to Therapsids to Mammals to Eutherians that begins with fishopods called Sarcopterygians. All modern mammals are still fish in that they are still Sarcopterygians. Now this doesn't mean that camels swim in water and have gills and scales. I means that all descendants of basal Sarcopterygians share characteristics with all other Sarcopterygians.
We have plenty of evidence from the fossil record and genetics showing this happened.
Discovery reveals evolutionary path from fins to fingers
show me any evidence of one species turning into another ...
You're going to first need to give me a hypothetical example of what you mean by "one species turning into another" We need to clarify that because many Creationists demand to observe something that actually would falsify evolution.
.give me a rational explanation of how life started explain to me how DNA changes ....like the DNA of a reptile becomes the DNA of a human
1. We don't know how life started but however it did does not effect evolution one single bit.
2. DNA changes through mutations. It can be as simple as a single base pair or it can be hundreds of base pairs. Many mutations are some of the best evidence for evolution come from gene, chromosome and even whole genome duplication followed by subsequent mutation.
3. The DNA of a human is not qualitatively different from that of a reptile. Both lines evolved from a basal Amniote population. If one looks at the entirety of the evolutionary history of a monitor lizard and a human, we have much more in common than we don't genetically.