Yo Mamma's Mitochondria

Not too long ago I read River Out of Eden by Richard Dawkins, and while the book was slow to start (I never can get too much into A's and G's and T's of DNA) it really did a good job of explaining how scientists know what they do about our evolutionary history.
One way specifically that process occurs is through examination of the DNA within our mitochondria.
You see, long long ago, waaaaaaay back before the dinosaurs mitochondria were a a self sustaining bacteria. That's why they have their own DNA. But somewhere along the way they teamed up with animals, and they've been happily living within us ever since. The cool thing about them is that they are only passed on from mothers to offspring. Whether you are male or female, your mitochondria came from your mother, and further back from your maternal grandmother and so on. It is an unbroken link (except for the occasional mutation) back through your maternal ancestry. As opposed to your normal DNA (which is mutated much faster due to the input by both parents, and thus more oppertunity for mistakes in copying), MDNA is much more stable, and easier to track. (The reason you don't get mitochondria from your father is because the there are none in the body of a sperm, There are a few in the tail, but they are discarded when the head of the sperm is enveloped by the egg.) The more differences between your mitochondria and someone else's, the longer ago it was that you were related. The smaller the differences, the closer to the present your and their ancestors diverged. It's kind of like the game "telephone" that kids play by whispering into each others ears. The further you pass the word along the more different it is likely to be from the original.
Far out isn't it? So next time you talk to your mom remember to thank her for your mitochondria. After all, if it wasn't for her you wouldn't have any.
P.S. Above drawing is by me. It is titled "Don't Talk About My Momma"