One third Irish?

kw: genealogy, family history

A guy announces that he's one-third Irish, and a friend challenges him, "That's impossible? How can you figure you are one-third anything?" He answers, "It isn't hard at all. My Mom isn't Irish at all, and my Dad is two-thirds Irish!"

I happen to be blessed with many ancestors who were good record-keepers, so I know a lot about my family heritage. I recently began gathering together all the information I have about the ancestors who were immigrants to America. I know that, except for a line of Cherokees, all of my ancestry goes through immigrants, but I don't know who the actual immigrants were in all cases. I can determine about 2/3 of my heritage at the moment, and I think I'll be able to increase that with a little more study.

If I add up the influence of each immigrant I know about (there are 152), it totals about 62% of the total. It works this way. A great-grandparent (three generations ago) has a factor of 1/8, or 12.5%, while a great-great-great-grandparent (five generations back) has a factor of 1/32, or 3.125%. Some of those 152 are 12 generations back, a factor of 1/4096 or 0.0244%. It takes a bunch of them to equal a great-great-grandparent.

So here is the approximate breakdown. Of the 62% I know, 22% (just over one third of the 62%), is English, and 21% is Irish. Less than half the rest is Welsh, a bit less is Scottish, and I have one known Cherokee line and one known German line, far enough back to be about 2% each. If those proportions fairly represent my entire heritage, then I am about 1/3 English and 1/3 Irish (But only "about", not exactly 1/3!). And that surprises me. I'd gotten the impression from the prominence of one Scottish line that I was mostly Scottish, but it is closer to 8%. The largest contingent, by a small margin, is English.