The recently re-posted puzzle of doubling ancestors was answered with an explanation of the theory of pedigree collapse which, albeit a valid point, disregarded a rather obvious mathematical fact. When a mating human pair produces more than two offspring the descendants simply outnumber the ancestors, nullifying the whole doubling ancestor question. I think that and boinking your cousin about covers it.
I don’t remember seeing this. Do you have a link?
Powers &8^]
I think it’s 2, 4, 8, 16 … how can you always have MORE ancestors as you go back in time? dated August 21, 1987.
Giles, thanks for posting that. jmastrus (et al.), just so you know for future, when you start a thread in reference to one of Cecil’s columns, it’s helpful to other readers to provide a link. Keeps us on the same page and saves searching time. No biggie, you’ll know for next time.
Carry on.
jmastrus said:
I don’t follow you. The question about doubling ancestors has nothing to do with how many relatives you currently have living. This is not a comparative between your ancestors vs your cousins.
It is a simple mathematical fact that it takes two parents for each child. Extend that mathematically back, and a single person should have 2 parents, 4 grandparents, 8 great-grandparents, 16 great-great-grandparents, 32 g-g-g-grandparents, etc. That doubling is mathematics of 2 parents to 1 child.
The fact that your granny had 37 kids does not in any way change the above math of 2:1. The only effect it has is the cousin-marrying affect. The second and the 34th kids from the above string of siblings each married and had children. Those children each had offspring. That generation of offspring then met and got hitched. Ancestor collapse. That kid’s mom and dad share a set of great-grandparents. That kid has 15 sets of g-g-grandparents.
I think his point was that if two parents have multiple children, all of those children have the exact same ancestry. So when making a comparative analysis of all the people alive today you would have to exclude full siblings.
Assuming mgalindo0824’s interpretation is correct, your mathematical fact is irrelevant. The doubling ancestors “problem” compares the theoretical ancestors of a single individual with population numbers in history. With no pedigree collapse, I, personally, would have had over a billion ancestors alive approximately 750 years ago. The world’s population at the time is estimated to be less than half that.
The fact that there’s 6 billion people alive today, many of whom probably don’t share any ancestors with me even that far back, makes the “problem” bigger, but although it’s hard to estimate by how much, that’s irrelevant to the initial question.
Cousins boinking is the only required explanation.
I’ll submit that cousins are not the only relatives who can contribute to the “pedigree collapse” phenomenon. Inter-generational couplings work just as well. The “common ancestor” is the main issue to removing place holders in a family tree’s layout. Interbreeding is also not a requirement, at least not the type that isolated societies (Appalachian groups for example) are accused of (and probably guilty of).
I know personally of several families whose sibling groups have been multi-generational due to the longevity of the survivors of multiple marriages/couplings and large families of partial siblings. The “yours, mine and ours” situation happens a lot in genealogical studies. And that’s normally just for the legitimate family members. I know of another real life situation where two half brothers in their 60’s are just now learning of two other partial sublings by way of their shared mother and another partial sibling by way of one of those by way of a shared father.
Small communities and ghettoes (enclaves may be a more polite term) provide fertile ground for interbreedings that many in the society are either unaware of or just don’t acknowledge for whatever reason. Think of communes and situations like Waco and Jonestown and the “one big happy family” concept. Yes, they nipped that potential ancestry nightmare in the bud, but still it’s an example to think about.
It’s fun to ask somebody, “How many ways are you kin to yourself?” And in many rural communities there may be no good way to tell!
Shouldn’t that be “at most 50th cousin”?
Powers &8^]
When I’ve tried to explain this to others, they invariably get caught up in the 7 billion people on earth issue, which is irrelevant. I tell them to assume that they’re the only person alive and then they seem to understand the question.
I only had one issue with this column:
Um … Probably? Is there some theory of human ancestry that would even allow for the possibility of a human being that isn’t in some way related to every other human being? 'Cause if there is, I’ve never heard of it.
However, apart from (grand)uncles/aunts with (grand)nieces/nephews, such relationships are called “cousins” in English, e.g., “third cousins twice removed”.
And even (grand)uncles/aunts with (grand)nieces/nephews counted as “cousins” in English only a few centuries ago.