Darwin's New Beginnings

The documentary/movie that was show in class on Thursday sparked some questions in my mind about Darwin and his theory of origins. After reading Darwin’s ‘Origins’ it was one thing to examine his writing and his absolutist rhetoric. However, to see a re-enactment of how he came to the conclusions in which he wrote about in his ‘Origins’ is completely different. While we have not finished the documentary and these questions I have may be answered in our next viewing of it, I find it beneficial to post now and develop these queries now.
Darwin states within the documentary that new beings can appear on the earth and thus creating a new species. This statement bothered me. If something is coming from pre-existing means, is it really new? When a cat has kittens, sure there are new kittens, but it is still just another cat. If one of these kittens shows a mutation that causes it to look and/or behave differently, it’s still a cat. It is no new species. However, over millions of years, this mutant-kitten may have further digressed in its descent from its common ancestor, but then, has a new species been created? It is simply a modified, degenerative form of the original. There is nothing new about it, so much as it is moreover different. However, to some, this may be the very criteria of ‘newness.’ However, I do not accept so far, that the million-year-descendant-mutant-kitten is a new species. It is a different species at this point, but there is nothing new about it.
Similarly, another question is one I have about science. Everyone in North America learns about Evolution in Science class in high school. Evolutionary theory states that we all have a common ancestor, yet, to my knowledge of going through the public school system and learning about Evolution, I have yet to find out what that common ancestor was. Everything in this theory is dependent upon one form, one being, one genetic cell even – yet that which the theory hangs onto, has not been identified. Furthermore, what is common enough that all species can descend from it? Not only species, but genera or geologies can descend from? It is stretching it to say that all animal life came from one common ancestor, but that does not account for plant life, rock formation or water. As professor Ogden has stated many times (and I agree), everyone believes in evolution; there’s no one who has ever not believed in evolution. However, to what extent people believe in evolution is what is in question. Darwin can state that we all have a common line of descent – but that is too easy. I want to know who was this common ancestor and what is DNA really the only thing common enough to unite the entire world through Evolutionary Theory? At what point does all of the science and numbers become simply science and numbers and not actually comprehensible?
Perhaps I am being legalistic in Darwin’s wording – but if he can be extremist in his views, that ‘new beings can appear on the earth’ then I can be extremist in picking it apart.