11 October 2008

We're all related

On Greg Laden's Blog, I've been joining the discussion a bit about race and its meaninglessness as a biological thing for humans. If you want to take that up, please join that thread. Here, I'm taking up the more genealogical side of relationship.

I've mentioned before that I've been doing some genealogy. This has included running mitochondrial and Y chromosome DNA samples. (Well, having someone else do so :-) The mitochondria pass solely from mother to child, so it gives a pointer on where my strictly matrilineal line comes from. The Y chromosomes pass strictly from father to son, so points to where the strictly patrilineal side comes from. In both cases 'points' is a generous description for something that really means 'within a few thousand miles, give or take a lot'. For the strictly patrilineal, I already 'know' the location outside the US (colonies as it turned out) -- Leonhart Krumbein of Strasbourg, who came in 1754 on the ship Brothers.

For the strictly matrilineal side, I had some hope of an interesting result. That side runs back to the early history of Maryland, and then is lost. Could have been that one of the women was a Native American. I'd have liked that. Unfortunately, both sides point to the most common haplogroups in Europe (H for the maternal side, R for the paternal). So no great surprises or novelty there. Oh well. It also established (not that this was a question) that I'm a mutant. (So are you, don't worry.) My mitochondria differ in 7 places (out of about 1500 checked) from the reference sequence. A little looking around shows one of the mutations to be fairly uncommon, even though the rest are very common.

By the time we're looking at 10 generations back (which is where I've tracked, loosely, the matrilineal side to), we've got 1024 ancestors. These tests only speak to 2 of those 1024. Quite a lot of variety could exist in the remaining 1022, but it won't show up in these two parts of our genome. At 20 generations back (about 1350), we've got about a million ancestors. That starts to get interesting, as it gets to be comparable to the population of significant areas (all of England at the time, for instance). Go to 30 generations (about 1050) and there are a billion ancestors -- greater than the population of the world at the time. Make it 40 generations, about 750, back to grandpa Chuck, and we've got a trillion ancestors -- more than 2000 times the world population of the time.

Grandpa Chuck is Charlemagne, who shows up in my tree. Given world population at the time, he probably shows up at least 2000 times in my tree if the whole thing were to be discovered. Back in college a friend (hi Derek) mentioned his descent from Charlemagne. This was before I knew about pedigree collapse so I was skeptical. Now that I do, it's more the converse -- it'd take evidence to show that you (for any of you, anywhere in the world) do not share him as an ancestor. Pedigree collapse is this business that as you go back in time, world population drops, but your number of ancestors keeps increasing. You hit a point where the same person must show up multiple times in your ancestry.

Related is that with a trillion slots to fill in your ancestry, even some connections that may seem intuitively unlikely are certain to happen. Intuition isn't a very good guide when numbers get large (among other times).

So I already know my real list of relatives -- everybody, everywhere. The only question would be how closely related we are. Even before starting the genealogy, I'd realized this. Even after greatly extending my knowledge of who came from where, 60% of the 'where' is still unknown. I take the rest of the world in that 60%.

5 comments:

AdamW said...

Steve Olson has a book "Mapping Human History" which covers this. His discussion has a more formal basis in a published study. I have the book, but not the paper.A quick search on GS threw up this, which looks like it might well be it:

http://adsabs.harvard.edu/abs/2004Natur.431..562R

Quite pertinently to the linked discussion above is this article (http://schools.tdsb.on.ca/rhking/departments/science/bio/evol_pop_dyn/does_race_exist.pdf) which has this paragraph:

"The results of these studies indicate that genetic analyses can distinguish groups of But caution is warranted.
people according to their geographic origin. But caution is warranted. The groups
easiest to resolve were those that were widely separated from one another geographically. Such samples maximize the
genetic variation among groups. When Bamshad and his co-workers used their 100 Alu polymorphisms to try to classify a
sample of individuals from southern India into a separate group, the Indians instead had more in common with either
Europeans or Asians. In other words, because India has been subject to many genetic influences from Europe and Asia,
people on the subcontinent did not group into a unique cluster. We concluded that many hundreds--or perhaps
thousands--of polymorphisms might have to be examined to distinguish between groups whose ancestors have historically
interbred with multiple populations."

I've only skim-read it so far. I'll read it properly later.

I'm currently reading "Seven Daughters Of Eve" by Bryan Sykes (just started), which is also proving interesting, and related.

Penguindreams said...

The first paper is also at
http://www.nature.com/nature/journal/v431/n7008/abs/nature02842.html, and gives the most recent common ancestor estimate as a few thousand years. Call it on the order of 100 generations. Awfully recent. When I first heard this (it's a 2004 paper) I was amazed, but then I started looking at the numbers, and learned how few infusions of 'outside influence' are needed to leave an observable influence in genomes.

The second and third notes you give subtly (which I'll make unsubtle) destroy, again, the notion of race as a biological concept. The thing is, biological races are defined by things which express themselves in the organism. The Alu's the second uses, and the mtDNA analyses used in the book, both depend on analysis of parts of our genome which don't express themselves.

Do let me know what you think of the book when you finish. Judging a book by its title (seldom chosen by the author in the first place) is even more removed than judging by its cover, but I confess I cringed at the title.

drj11 said...

There's a couple of amusing corollaries that I picked up recently from Dawkins' "Ancestor's Tale": If you go back far enough then you reach a point where someone who was alive then is the (an) ancestor of everyone alive today. In fact there are several such people. Keep going back and you soon reach a time when _everyone_ alive then is the ancestor of everyone alive today.

AdamW said...

I've not forgotten to post what I think of the Sykes book. I'm only halfway through at the moment - having very young children in the house is reducing reading time.

That said, despite the title (I had to look up who Brian Sykes was before buying it put me off so much), I'm enjoying it so far. It's at a bit of a different level to the Olson book, but there's some good overlaps and the writing is entertaining, as well as some of the anecdotes.

As a layman, it's interesting just how ad-hoc this early genetic research was (DNA didn't strike me as lending itself to that approach but it shows how all science can, I guess). Also when Sykes discusses how laborious early DNA techniques were in the early '90s and how "now" there's sophisticated machines to do a lot of it, it's easy to forget that the book was written less than ten years from the period he's discussing. This shows how rapidly this field has progressed.

AdamW said...

Well I did enjoy the book. The controversies were naturally discussed from one point of view, but were diplomatically handled. There was some good detail fleshing out the European discussion that I remember from Olson's book (though I did read that some time ago, I might have to re-read it), and the "World" section at the end is a summary of a lot of Olson's book.

The descriptive bits of each of the women is probably unnecessary, but I enjoyed them to some extent - I finished the rest of the book and came back to them as if they were a separate document.

Thye very last chapter is in danger of stretching this a bit, almost straying into metaphysical ideas, but he does get to spend a lot of time thinking about this stuff.

All in all a good book, despite the title (which seems to appear 'titlised' all through the book, and suggests maybe an external influence and a search & replace, but that's a guess). It's obviously a bit behind the times now and just to see the advances in the decade up to its publish date, suggests it could be considerably behind now.

I'll look for a more up to date one to read in a year or two, when I get through my current reading pile (which includes some AR4 chapters....)