February 14th, 2011

Genealogy: what's the phrase for that?

Family trees are only trees when viewed from the perspective of a single "I": my ancestors branching above me, my descendants in the roots below me (or vice versa) and me, the trunk. Otherwise, technically speaking, they are directed graphs (with undirected links between spouses, I suppose).

In any event, musing about genealogy leads to a befuddling question: that branching in the ancestry can't really just keep going, two parents for each person going back forever. There's a phrase for that (and it doesn't seem to be demographic collapse). I just can't remember what it is.

2 of my 4 grandparents are known to have entirely Dutch ancestry (to the extent that that means anything, cf. European history). 1 of my grandparents has substantial Dutch ancestry, within the context of a religion that emphasized in-marriage. I've had a self-pubbed genealogy for that last grandparent since I was a child and I knew perfectly well that there were people getting married who had the same (not real common) last name. More recently, I stumbled across a Poldervaart-Poldervaart marriage in the Netherlands which surprised me (collateral, IIRC).

Here's what I didn't expect to find. That fourth grandparent is the product of a first cousin marriage. So I have 2 fewer grgrgr grand parents than the equation predicts.

On a related note, you know how people who get overly excited about even the hint of the suggestion of a possibility of someone doing something naughty often turn out to have some connection to same in their own life? Yeah, that'd be my parent, the child of that grandparent.