I have inherited a not-so-frequent patronym, of which origin is still unclear. My paternal line tracks back with good confidence up to Jean Vatant (abt.1673-1723), in the heart of Brittany. The name is rare in this region, all its bearers were somehow relatives. But it does not make any sense in Brezhoneg, the local language, so it was probably imported there long ago. From where remains unknown. It can be found in some other regions of France, such as Burgundy, and around the eponym village in the center of France, although that one is lacking the trailing "t", which is not a detail. In Brezhoneg, the trailing "t" was certainly pronounced, more or less as in English "blatant", and records written by Brezhoneg-speaking priests or officers never mispell it. In French it's not pronounced, and late 1800s records often forget it.
Most of all other ancestors of mine, both on paternal and maternal side, bear honest Brezhoneg peasants names, such as Favennec, Corre, Le Du, Penanguer, Hamonou, Jégou, although a pinch of more no(ta)bles can be found in the 1600s, such as Catherine de Kerenor (abt.1630-1704).
I'm also monitoring what's going on in the far-away branches of the Big Tree, with a team of bold "Outer Rim Rangers".
We are all cousins. And in a very extensive meaning of "we", see Evogeneao showing how all living creatures on this planet, not only all of us humans, but all animals, tigers, bees, snakes, snails, and also trees, mushrooms and even bacteria, all belong to the same Big Family. The Tree of Life is a "Single Tree".
That said, it's very likely, dear fellow WikiTreer, that you and me will never know by her name a single one of our common ancestors if the most recent ones were living before 1400. To begin with, I don't and will never know with a reasonable level of confidence any of my ancestors that far away.
And suppose we ever find one such medieval common ancestor, over 20 generations ago. The probability for one at least of the links (in either or both lines connecting us to her) to be wrong is fairly high. Even if you have a 99% mean confidence for every filiation link to be correct, the probability of the entire line to be correct, back and forth, is 0.99^40 = 0.67. Far from certainty ...
And 99% mean confidence for each step back and forth over 20 generations seems a very bold assumption indeed. If you take a more conservative estimation, like 95%, you come out with a probability of 0.95^40 = 0.13 to be correct. Otherwise said, 87% of chances for this connection path to be wrong somewhere. And if you are overly cautious and say the mean confidence is 90%, you end up at more than 98% of chances to be wrong.
Let's not nitpick on figures. The conclusion is : forget it, it's not worth the trouble of so many nights passed over dubious old scribblings. There is a lot to do in more recent generations, and with a higher level of confidence, without going backward much before 1800. That's why I focus on the late 1800s and early 1900s, the Belle Époque through which, my fellow genealogists, I believe we can be connected by some cousins of cousins of in-laws.
My dear aunt Sidonie used to say : On hérite de sept générations! Of course she knew our ancestors lines extend far beyond those seven generations, but that was putting a reasonable horizon to the genealogical research.
More on this here : Shapes in the Great Tree
Bernard is 27 degrees from Isaac Asimov, 28 degrees from David Attenborough, 29 degrees from Bill Bryson, 25 degrees from Richard Dawkins, 34 degrees from Bengt Feldreich, 37 degrees from Ruth Gates, 31 degrees from Stephen Hawking, 37 degrees from Julius Miller, 26 degrees from Bill Nye, 30 degrees from Magnus Pyke, 31 degrees from Carl Sagan and 26 degrees from David Randall on our single family tree. Login to find your connection.