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Treebeard's Stumper Answer
22 October 1999

Too Many Ancestors

I have two parents, and so do they. That gives me four grandparents and eight great-grandparents. Details get fuzzy after that, but I'm sure my family tree keeps doubling every generation: 16, 32, 64, 128, 256, and so on. After 10 generations, I'm back to the founding of our country with 1,024 of my ancestors on the loose. After 20 generations, I have over a million ancestors. After 30 generations, I have a billion ancestors. But that's far more than the (then) population of the world! That's impossible! How does my family tree narrow down?

Everyone has two parents, but we soon find too many ancestors! The answer must be that our ancestors are not all distinct. I might be descended from more than one child of a couple. The same person may turn up twice in my family tree by remarrying. People do sometimes marry "distant cousins," and I'm sure this was more common in the past when people were more tied to small town life with limited populations and social opportunities. There must be many such duplications to prune down every family tree. Perhaps we really are all related?


I think we're all cousins on this bus...

Ancestors pile up quickly as we go back in time. Figuring 25 years per generation (20 or even 15 years might be a better guess as we go further back), I get:

Generation My Ancestors Date
My parents21925
My grandparents41900
3rd generation81875
4th generation161850
5th generation321825
6th generation641800
7th generation1281775
8th generation2561750
9th generation1,0241725
10th generation2,0481700
11th generation4,0961675
12th generation8,1921650
13th generation16,3841625
14th generation32,7681600
15th generation65,5361575
16th generation131,0721550
17th generation262,1441525
18th generation524,2881500
19th generation1,048,5761475
20th generation2,097,1521450
21th generation4,194,3041425
22th generation8,388,6081400
23th generation16,777,2161375
24th generation33,554,4321350
25th generation67,108,8641325
26th generation134,217,7281300
27th generation268,435,4561275
28th generation536,870,9121250
29th generation1,073,741,8241225

Graybear gives this elegant answer:

We will find, as we fill in our trees, that we are soon able to trace back to a particular ancestor by more than one path. A friend of mine has traced her geneology back to Pocahontas in three different ways. In other words, our ancestors are cousins. If you go back far enough, each path will connect through Noah and his wife, and we will realize we are all (distant) cousins. This is one of the reasons that people who claim to believe the Biblical account of the flood have no excuse for prejudism. (The other reason is the second greatest commandment - Love your neighbor as yourself.) When we entered the space-age, we became aware that we are all neighbors on little blue-green island in the Milky Way. Maybe we should invite all of our neighbors for a world party...

Whether we trace our roots back to Adam or Lucy, I think the results are the same. Every duplication prunes the tree. In the end, we're all cousins, and our family trees will show it if we look close enough.

The first story I ever read by R.A. Lafferty was his "Nine Hundred Grandmothers" in his 1970 ACE story collection of the same name. Nobody tells a tale like R.A. Lafferty! In this story, explorers find the planet Proavitus where the inhabitants are immortal. But they get smaller and smaller as they grow older, and mostly sleep. They live on shelves in the basement:
Smaller and older the creatures had been getting... The wren-sized grandmother talked and laughed and nodded that there were those far older than herself, and in doing so she nodded herself back to sleep... What was that sound - too slight, too scattered to be a noise? It was like a billion microbes laughing. It was the hilarity of little things waking up to a high time...
Imagine all your ancestors in one place, and you can ask them questions! Read this story to find what the oldest grandmother says! There's a web site dedicated to R.A. Lafferty's great stories. Many of his books are now out of print, but try an author search at Amazon.Com.

This stumper has been discussed on the Web, and there are many geneology sites:

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