Who was my ancestor?

I have blue eyes, not terribly unusual, but apparently of an interesting origin. According to this article all people with blue eyes have a single ancestor. A mutation arose in that ancestor some time in the past 6,000 to 10,000 years. The mutation occurs in a gene adjacent to the OCA2 gene which regulates the production of melanin. Apparently in the iris the mutation “slows down” the OCA2 gene leading to relatively less melanin and thuse the blue shade of the iris.

The study tracked down this mutation across a wide population and through analysis of the  long haplotypes concluded when the mutation occurred (obviously only approximately). The study only covered people from Jordan to Denmark but for me it raises the question of how these mutation spread, i.e. how related are the people from these regions over only such a short period. The study humorously concludes that the fixing of the mutation in 20-30% of the population must be due to mates finding blue eyes more attractive (although, WHY, would be an interesting question for evolutionary psychology). But all this does indicate a lot more mixing up of the populations of Europe and the near Middle East than I’d previously thought was the general prediction.

Now ‘ancestor’ is one of those misleading thing. It doesn’t mean all the people with blue eyes are my cousin. AFAIK the mutation is recessive, so my dad, who had blue eyes had two copies, and my mother, who didn’t, had one copy, and thus I managed to get the mutation from both parents. But let’s think about ancestors. For convenience let’s assume three generations per hundred years and assume the most recent date for emergence of this mutation, i.e. 6000 years, or 60 centuries, which means 240 generations ago. That nominally means I have 2^240 ancestors, one of which includes that original individual with the first instance of the mutation. I’ve seen estimates that the total number of humans that have ever existed is around 100 billion (let’s use 64 billion for convenience) which is 2^36 people. That means vast numbers of my possible 2^240 “unique” ancestors are in fact the same person but one thing is certain, all my actual ancestors had at least one copy of the mutation so that eventually I’d end up with two copies.


About dmill96

old fat (but now getting trim and fit) guy, who used to create software in Silicon Valley (almost before it was called that), who used to go backpacking and bicycling and cross-country skiing and now geodashes, drives AWD in Wyoming, takes pictures, and writes long blog posts and does xizquvjyk.
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3 Responses to Who was my ancestor?

  1. Nona says:

    I think we could be cousins. I have blue eyes, along with a brother, from our Dad. We were able to trace ancestry back to 700’s with a royalty of some sort in Denmark. I found I was the 26th great granddaughter of Robert Bruce, the 1st king of Scotland. I didn’t believe it so we re-did (what a horrible word) it again to check for a mistake. My fathers grandmother was my mother’s great aunt. Coming from parents who were second cousins in Mississippi turn of the century was not uncommon back then due to the decimation of men in Civil War. I refer to us as Arkansas royalty, one limb family tree.

    • dmill96 says:

      Interesting. In a sort of silly way, we have to be cousins since blue eye trait is recessive and at one point in human history only one person probably had this mutation (co-evolution of mutations is certainly possible, but improbable). Of course that could be a thousand generations back and that far back we undoubtedly have multiple common ancestors.

      I don’t have a very accurate family history since my (still alive, 98YO) mother tends to fantasize ancestors for which I see little evidence (one family member did do a lot of research and found no one of notable significance).

      People are clearly more related than they imagine. Even now with rapid digitization of records (mostly of European people and their descendants) and tools like ancestory.com this is still only a brief period in human history. The rest is mostly lost. Some of the earlier genomic efforts to uncover ancestors (like the “ancestral Eve” have now been discredited since they were done before high volume and complete coverage genomic sequencing was available and now with more complete data, plus the bioinformatic software, some of those early conclusions are proving inaccurate. But, nonetheless, everyone alive today is descended from a relatively small number of common ancestors, perhaps as little as 8-12,000 years back.

  2. Pingback: What is the point of blogging? | dailydouq

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