As I've mentioned here on more than one occasion, I'm an avid genealogist. (I call the hobby, 'looking for my dead people.')
I've been researching my family tree for 25+ years now and I've gotten pretty damned good at it.
But several years ago, quite early on in my research as a matter of fact, I discovered a most interesting revelation about my ancestry. I've traced my paternal grandmother's French-Canadian ancestry (on her father's side) back to the 1500s and it turns out that I am my own cousin, many times over.
This phenomenon is not unique to my family tree. A surprising number of Quebeckers can trace their family histories back to the settlement era of the mid-1600s. Many of the original families married amongst themselves, and still do, resulting in Quebec's gene pool being particularly unalloyed, so much so that researchers wanting to isolate specific genetic characteristics -- such as obesity, or proneness to having twins, or certain heart conditions, or diabetes -- conduct their studies in Quebec.
Descendants of the Labrosse/Malette union are descended from more than one couple more than one time, making me both the 8th and 9th great-granddaughter of one marriage; and also the double 8th great grand-daughter of another marriage. Here's how it works.
Mathurin Benard and Marguerite Viard were the parents of Jeanne and Marie (sisters). Jeanne's 2nd great grand daughter (Clemence Biroleau) married Marie's great grandson (Joachim Legault). Joachim Legault and Clemence Biroleau were my 4th great grandparents (the grandparents of Adeline Legault - my 2nd great grandmother). Since Clemence's 2nd great grandmother and Joachim's great grandmother were sisters, their parents were both my 8th and my 9th great grandparents.
Since discovering these two lines of descent from the above two couples, I have established that there are several other couples from whom I have two lines of descent, and there are three couples from whom I have three lines of descent.
The computer software I use to track all this information gives me one person's relationship to any other person on the tree. A kinship report of my own name indicates that I am my own cousin thirteen different ways: 7th cousin; 8th cousin; 8th cousin 1x removed; half 8th cousin 1x removed; 9th cousin; 9th cousin 1x removed; 10th cousin; 9th cousin 2x removed; 10th cousin 1x removed; 11th cousin; 10th cousin 2x removed; 11th cousin 1x removed; and 12th cousin.
Of course, since I'm related to myself, I'm also related in a similar fashion to each of my siblings, to my parents and my paternal grandparents (and by extension, to my daughter and grandson).
Admittedly, the inter-relationship is far enough removed to render it insignificant today -- but it is fun to be able to say: "I should quit researching before I find out that I am my own grand-maw!"