A Primer on Second Cousins Once Removed

Over the weekend I was telling a friend about the daughter of my granddad's brother. And I stumbled. What was she? A second cousin? A cousin once removed? I had no idea.

At 50, I had never mastered these terms. For years, I have read that the U.S. presidents Theodore and Franklin Roosevelt were fifth cousins. And for years, I have not understood what on earth that meant.

Now I do. Theodore and Franklin Roosevelt shared the same great-great-great-great-grandparents and were from the same generation. And the daughter of my granddad's brother is a second cousin, once removed, since our families shared the same great-grandparents (the "second cousin" part) but are from different generations (the "once removed" part).

Confused? To brush up on these terms, read this primer:

Second cousins. You share the same great-grandparents.

Third cousins. You share the same great-great-grandparents. And so on.

Removed. You hail from different generations. "Once removed" means you're one generation apart, and "twice removed" means you're two generations apart. And so on.

Now you can figure out whether a relative is truly your cousin Vinny (as opposed to your second cousin Vinny).

Meanwhile, many famous people have married various types of cousins. Thomas Jefferson wed his third cousin. Johann Sebastian Bach and Albert Einstein tied the knots with their second cousins, and Rudy Giuliani did so with his second cousin, once removed. Jessie James and Charles Darwin married their first cousins. Jerry Lee Lewis married his (13-year-old) first cousin, once removed.

Times have changed. Today 25 states prohibit marriages between first cousins, according to the National Conference of States Legislatures. (California and New York allow it.)

I'm off to go figure out a few more common ancestors.

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