Wednesday, August 19, 2015

Quantifying Genealogy

As I have progressed on my genealogy journey I have constantly wondered of ways to quantify how much I know about my own genealogy. Was there a way I could determine how much of my family history I knew? After looking at random statistics and doing different calculations there were two things I found very interesting in terms of quantifying my genealogy; the number of ancestors I knew about (at least a name, a birth date, or a death date) per generation back and the total number of ancestors I truly had in each generation. I could easily put these together to find out an assumed percentage of how many ancestors I knew about in each generation. I decided to make a post about it although it could be considered rambling by some.

Here is what I have in basic knowledge for up to 8 generations

Parents - 2/2 = 100%
Grandparents - 4/4 = 100%
Great Grandparents - 8/8 = 100%
2nd Great Grandparents - 12/16 = 75%
3rd Great Grandparents - 12/32 = 37.5%
4th Great Grandparents - 8/64 = .125%
5th Great Grandparents - 15/128 = .117%
6th Great Grandparents - 24/256 = .094%
7th Great Grandparents - 41/512 = .08%  
8th Great Grandparents - 65/1024 = .063%

Looking over it this seems pretty straightforward but when you interpret what it means it really puts things into perspective. For example lets take my 8th great grandparents who were all mostly born between 1650-1700, about 365 to 415 years ago, I know about only 65 completely different ancestors living at that time. Yet those 65 almost make up 2/3 of only 1 percent of the ancestors I had alive at the time throughout the whole world. As well it shows just how much information I lack and how much there is for me to try to obtain, so it gives me inspiration to knock down those brick-walls to discover all that information I don't know about the ancestors I come from.

Now if I go back two more generations things get very interesting because this is the first generation where I know I have ancestors show up multiple times.

9th Great Grandparents - 59/2042 = .029%
10th Great Grandparents - 43/4084 = .011%

If you look closely you will realize that instead of 2048 9th-great grandparents I only list 2042. This is because I have 3 sets of 9th great grandparents who I descend from twice. Each subsequent generation back in time will now go from this number until another generation with ancestors who I descend from more than once changes the number again. I find it an interesting concept because it relates to the pedigree collapse theory, that over time you will eventually have more ancestors than people living in the world. So lets say you have a set of 2nd great grandparents you descend from twice you would have 14 sets of 2nd great-grandparents instead of the usual 16, then take that back 5 more generations to 7th great grandparents and you've got 456 ancestors at most instead of 512, a difference of 56 ancestors. Take it back to your 10th great grandparents and you've got at most 3648 ancestors instead of 4096, a difference of 448 ancestors. Then once you consider that each generation you go back there is an even higher likelihood of more common ancestors within your own tree the actual number of ancestors you descend from could be quite less than you truly anticipate.