Everything with MtDNA shares a distinctive linage (that is all Eukaryotes). Think of it as a branching tree. The first big branch happens between Plants and Not Plants. Then Fungi and Animals and so on. MtDNA shows that we shared a common ancestor Neanderthals 750,000 years ago, with chimpanzees 5-7 million years ago. (and that chimps are far more genetically diverse than we are)
MtDNA has been used to create what are called supertrees. Phylogenies for living species.
here is the Mammal supertree.
http://www.sciencemag.org/content/vol291/issue5509/images/data/1786/DC1/1056346s1rev1_large.jpeg
Creationists love the human Mt-Eve but they hate to talk about the other Mt-eve's out there.
The important thing to remember is that just because Mt-mrca (most recent common ancestor) is our MRCA doesn't mean that she was the only person living at the time. We have more than one or two human fossils from the time for a start.
One other thing Creationists don't like to mention is that you can do the same thing with the Y chromosome. "Y-chromosome Adam" as he's called is the last shared common ancestor for all males. He lived around 60,000-90,000 years ago. A minimum of 30,000 years (or about a thousand generations) after 'Eve'. Like Mt-Eve he wasn't the only human in existance though his mother was possibly a decendant of Mt-Eve.
The real genetic prize is LUCA (Last Univeral Common Ancestor) that one lucky organism that gave rise to all modern life on Earth. Somehow LUCA had an advantage that let it reproduce faster and survive better than the other early lifeforms. LUCA became the DNA template from wich all living things decended. Bacteria to Corn to Humans.
wa:do
