Indeed. Species is something that humans invented, we can't give a clear definition to it. Therefore, your argument that a species can't evolve into anotherspecies doesn't make sense.

Well there's a chance your kids can be born with a tail, fused mermaid legs or webbed fingers and/or toes. There's no more advantage to that nowadays so those mutations (or rather switches) are going nowhere. Currently humans are mostly breeding for low IQ :p

Over time your ancestors can sprout wings. The human species will need to shrink a lot first, a long period of nuclear winter or global warming exciction event should suffice to shrink species. Webbed arms can become advantageous to increase jump distance by gliding (like certain squirrels in the Amazon) Flight already evolved 4 seperate time before https://www.scienceworld.ca/blog/evolution-flight so get rid of civilization (works against evolution), make it very hard to survive, wait serveral hundred million years and increase the oxygen content a bit to favor high energetic actions.

If you expect it to breed something completely new which fails to be categorized as a dog, then you do not understand evolution.

Evolution as been proven. Maybe there are missing links to explain exactly where humans are coming from, so that one is still out for debate.
But evolution of species in general? It's a fact, every living thing on the planet is in constant evolution ,a species that can't evolve is a dead species.

Sigh.  You seem confused and you need to read it yourself aparently.  Posters saying "It's not a theory, it's a fact" do not understand the meaning of scientific theory.  And you do not understand the meaning of believe, which is simply again, "taken to be true".

To say "I belive in the evolution theory" is to say "I take evolution, which has been tested over time enough to be scientifically proven, to be true".  To say it doen't take "belief" and "it's fact not theory" is to not understand the meaning of the words.  And that actually includes you, as you don't understand the meaning of believe.  That's natural, as people often use the word incorrectly today as a substitute for believing without facts.  It's from the Bible line where Jesus says "Blessed are those who have not seen, and yet believe".  As a result, people often include the two ideas together these days, but the "believing" part and the "not seen" part are actually not connected.  Believing simply means to take as truth.

Double LOL.  Did you even read what I said?  Someone saying "It's not a theory, it's a fact" do not understand the meaning of "theory" as used in science.  They are essentially saying "It's not a proven idea with lots of reasearch over a prolonged period of time, it's a fact".  Actual scientists generally steer away from the word "fact" - and other absolutes - as it implies closed-mindedness.  Evolution is very, very, very likely true, but as a scientific community we will continue to research it and find things we don't yet understand.

Yes. You can even see in a human embryo at 4 weeks or so that the fetus has a small tail which it discards as the pregnancy goes along. This is why your "tail bone" is called your "tail bone".

There's no reason for things like that to happen if we're a unique, completely unconnected singular species.

Starfighter, what you're both saying is correct in a way. Neither of you are wrong.
Evolution is fact.
Evolution is also theory.
The problem, is that the English language uses theory in a different way. The whole problem would be solved of the word theory was replaced by the word explanation.
The explanation of evolution is the only thing we cannot fully explain. Theories are constantly evolving in order to include more info, but they are rarely significantly changed in meaning.
It's true that scientists use theory in a non-constant way, but it doesn't make it less factual.
For example, let's make a situation where there is a "theory of alphabet" which would say the alphabet is a series of symbols that represent sounds commonly found in english vocal range, and used to convey those words in a published format.
If one day we were able to convert letters into colors, the "theory of alphabet" might have to be altered to cover a non-publicated or audible format.
It doesn't mean the alphabet isn't there plain for anyone to see, it just means that there is more to explain "why" the alphabet is what it is.

Maybe a dull example, but the quickest I could think of off the top of my head.

For further reference, look up the evolving theory of gravity, with research done by a recent scientist that might alter the definition slightly in order to account for dark matter.

Triple LOL. Did you read what a scientific theory is? Do you actually know what a fact is? 

Fact:

That's not correct, and your example is ironically a good one.  Evolution is not a fact, because it is not indisputable.  There have been silly people that have said dinosaur bones were put in the ground to tempt us.  This is extremely likely to not be true, but since none of us were there to see the bones get in the ground, we can't say, indisputably, that it didn't happen.  And scientists, such as myself, keep an open mind to all options, no matter how ridiculous.  And that's why we use the term scientific theory.  It is accepted as truth, but like most scientific observations of our natural world, is not and likely never will be, indisputable. 

The term "fact" should be reserved for human-defined concepts or observations in nature that have been 100% observed.  The alphabet, for example, is a human created idea. We don't have a theory to describe it, because it was created by us. We defined what it is.  The alphabet starts with "A".  This is a fact, because it's human creators decided this was to be.

Until we talk to whoever made evolution, or develop a time machine to observe its beginnings through to its end, it will remain a scientific theory which means it's really, really, really likely true, and what people are trying to say when they say it's not a theory, it's a fact. They just don't understand what theory means.