The bad news is that it has generated hundreds of e-mails every day – and I can’t possibly answer them all personally. So, if you’ve written me and I don’t reply, I apologize and I hope you’ll understand. Many of the questions I’ve received are similar in nature and I’m going to answer them in this article. In essence, people who have matches want to know what they mean.
Q – I had a match at GedMatch to <fill in the blank ancient DNA sample name> and I want to know if this is valid.
A – Generally, when someone asks if an autosomal match is “valid,” what they really mean is whether or not this is a genealogically relevant match or if it’s what is typically referred to as IBS, or identical by state. Genealogically relevant samples are referred to as IBD, or identical by descent. I wrote about that in this article with a full explanation and examples, but let me do a brief recap here.
In genealogy terms, IBD is typically used to mean matches over a particular threshold that can be or are GENEALOGICALLY RELEVANT. Those last two words are the clue here. In other words, we can match them with an ancestor with some genealogy work and triangulation. If the segment is large, and by that I mean significantly over the threshold of 700 SNPs and 7cM, even if we can’t identify the common ancestor with another person, the segment is presumed to be IBD simply because of the math involved with the breakdown of segment into pieces. In other words, a large segment match generally means a relatively recent ancestor and a smaller segment means a more distant ancestor. You can readily see this breakdown on this ISOGG page detailing autosomal DNA transmission and breakdown.
Unfortunately, often smaller segments, or ones determined to be IBS are considered to be useless, but they aren’t, as I’ve demonstrated several times when utilizing them for matching to distant ancestors. That aside, there are two kinds of IBS segments.
One kind of IBS segment is where you do indeed share a common ancestor, but the segment is small and you can’t necessarily connect it to the ancestor. These are known as population matches and are interpreted to mean your common ancestor comes from a common population with the other person, back in time, but you can’t find the common ancestor. By population, we could mean something like Amish, Jewish or Native American, or a country like Germany or the Netherlands.
In the cases where I’ve utilized segments significantly under 7cM to triangulate ancestors, those segments would have been considered IBS until I mapped them to an ancestor, and then they suddenly fell into the IBD category.
As you can see, the definitions are a bit fluid and are really defined by the genealogy involved.
The second kind of IBS is where you really DON’T share an ancestor, but your DNA and your matches DNA has managed to mutate to a common state by convergence, or, where your Mom’s and Dad’s DNA combined form a pseudo match, where you match someone on a segment run long enough to be considered a match at a low level. I discussed how this works, with examples, in this article. Look at example four, “a false match.”
So, in a nutshell, if you know who your common ancestor is on a segment match with someone, you are IBD, identical by descent. If you don’t know who your common ancestor is, and the segment is below the normal threshold, then you are generally considered to be IBS – although that may or may not always be true. There is no way to know if you are truly IBS by population or IBS by convergence, with the possible exception of phased data.
Data phasing is when you can compare your autosomal DNA with one or both parents to determine which half you obtained from whom. If you are a match by convergence where your DNA run matches that of someone else because the combination of your parents DNA happens to match their segment, phasing will show that clearly. Here’s an example for only one location utilizing only my mother’s data phased with mine. My father is deceased and we have to infer his results based on my mother’s and my own. In other words, mine minus the part I inherited from my mother = my father’s DNA.
|My Result||My Result||Mother’s Result||Mother’s Result||Father’s Inferred Result||Father’s Inferred Result|
In this example of just one location, you can see that I carry a T and an A in that location. My mother carries a T and a G, so I obviously inherited the T from her because I don’t have a G. Therefore, my father had to have carried at least an A, but we can’t discern his second value.
This example utilized only one location. Your autosomal data file will hold between 500,000 and 700,000 location, depending on the vendor you tested with and the version level.
You can phase your DNA with that of your parent(s) at GedMatch. However, if both of your parents are living, an easier test would be to see if either of your parents match the individual in question. If neither of your parents match them, then your match is a result of convergence or a data read error.
So, this long conversation about IBD and IBS is to reach this conclusion.
All of the ancient specimens are just that, ancient, so by definition, you cannot find a genealogy match to them, so they are not IBD. Best case, they are IBS by population. Worse case, IBS by convergence. You may or may not be able to tell the difference. The reason, in my example earlier this week, that I utilized my mother’s DNA and only looked at locations where we both matched the ancient specimens was because I knew those matches were not by convergence – they were in fact IBS by population because my mother and I both matched Anzick.
Q – What does this ancient match mean to me?
A – Doggone if I know. No, I’m serious. Let’s look at a couple possibilities, but they all have to do with the research you have, or have not, done.
If you’ve done what I’ve done, and you’ve mapped your DNA segments to specific ancestors, then you can compare your ancient matching segments to your ancestral spreadsheet map, especially if you can tell unquestionably which side the ancestral DNA matches. In my case, shown above, the Clovis Anzik matched my mother and me on the same segment and we both matched Cousin Herbie. We know unquestionably who our common ancestor is with cousin Herbie – so we know, in our family line, which line this segment of DNA shared with Anzick descends through.
If you’re not doing ancestor mapping, then I guess the Anzick match would come in the category of, “well, isn’t that interesting.” For some, this is a spiritual connection to the past, a genetic epiphany. For other, it’s “so what.”
Maybe this is a good reason to start ancestor mapping! This article tells you how to get started.
Q – Does my match to Anzick mean he is my ancestor?
A – No, it means that you and Anzick share common ancestry someplace back in time, perhaps tens of thousands of years ago.
Q – I match the Anzick sample. Does this prove that I have Native American heritage?
A – No, and it depends. Don’t you just hate answers like this?
No, this match alone does not prove Native American heritage, especially not at IBS levels. In fact, many people who don’t have Native heritage match small segments? How can this be? Well, refer to the IBS by convergence discussion above. In addition, Anzick child came from an Asian population when his ancestors migrated, crossing from Asia via Beringia. That Eurasian population also settled part of Europe – so you could be matching on very small segments from a common population in Eurasia long ago. In a paper just last year, this was discussed when Siberian ancient DNA was shown to be related to both Native Americans and Europeans.
In some cases, a match to Anzick on a segment already attributed to a Native line can confirm or help to confirm that attribution. In my case, I found the Anzick match on segments in the Lore family who descend from the Acadians who were admixed with the Micmac. I have several Anzick match segments that fit that criteria.
A match to Anzick alone doesn’t prove anything, except that you match Anzick, which in and of itself is pretty cool.
Q – I’m European with no ancestors from America, and I match Anzick too. How can that be?
A – That’s really quite amazing isn’t it. Just this week in Nature, a new article was published discussing the three “tribes” that settled or founded the European populations. This, combined with the Siberian ancient DNA results that connect the dots between an ancient population that contributed to both Europeans and Native Americans explains a lot.
If you think about it, this isn’t a lot different than the discovery that all Europeans carry some small amount of Neanderthal and Denisovan DNA.
Well, guess what….so does Anzick.
Here are his matches to the Altai Neanderthal.
|Chr||Start Location||End Location||Centimorgans (cM)||SNPs|
He does not match the Caucasus Neanderthal. He does, however, match the Denisovan individual on one location.
|Chr||Start Location||End Location||Centimorgans (cM)||SNPs|
Q – Maybe the scientists are just wrong and the burial is not 12,500 years old, maybe just 100 years old and that’s why the results are matching contemporary people.
A – I’m not an archaeologist, nor do I play one…but I have been closely involved with numerous archaeological excavations over the past decade with The Lost Colony Research Group, several of which recovered human remains. The photo below is me with Anne Poole, my co-director, sifting at one of the digs.
There are very specific protocols that are followed during and following excavation and an error of this magnitude would be almost impossible to fathom. It would require kindergarten level incompetence on the part of not one, but all professionals involved.
In the Montana Anzick case, in the paper itself, the findings and protocols are both discussed. First, the burial was discovered directly beneath the Clovis layer where more than 100 tools were found, and the Clovis layer was undisturbed, meaning that this is not a contemporary burial that was buried through the Clovis layer. Second, the DNA fragmentation that occurs as DNA degrades correlated closely to what would be expected in that type of environment at the expected age based on the Clovis layer. Third, the bones themselves were directly dated using XAD-collagen to 12,707-12,556 calendar years ago. Lastly, if the remains were younger, the skeletal remains would match most closely with Native Americans of that region, and that isn’t the case. This graphic from the paper shows that the closest matches are to South Americans, not North Americans.
This match pattern is also confirmed independently by the recent closest GedMatch matches to South Americans.
Q – How can this match from so long ago possibly be real?
A – That’s a great question and one that was terribly perplexing to Dr. Svante Paabo, the man who is responsible for producing the full genome sequence of the first, and now several more, Neanderthals. The expectation was, understanding autosomal DNA gets watered down by 50% in every generation though recombination, that ancient genomes would be long gone and not present in modern populations. Imagine Svante’s surprise when he discovered that not only isn’t true, but those ancient DNA segmetns are present in all Europeans and many Asians as well. He too agonized over the question about how this is possible, which he discussed in this great video. In fact he repeated these tests over and over in different ways because he was convinced that modern individuals could not carry Neanderthal DNA – but all those repeated tests did was to prove him right. (Paabo’s book, Neanderthal Man, In Search of Lost Genomes is an incredible read that I would highly recommend.)
What this means is that the population at one time, and probably at several different times, had to be very small. In fact, it’s very likely that many times different pockets of the human race was in great jeopardy of dying out. We know about the ones that survived. Probably many did perish leaving no descendants today. For example, no Neanderthal mitochondrial DNA has been found in any living or recent human.
In a small population, let’s say 5 males and 5 females who some how got separated from their family group and founded a new group, by necessity. In fact, this could well be a description of how the Native Americans crossed Beringia. Those 5 males and 5 females are the founding population of the new group. If they survive, all of the males will carry the men’s haplogroups – let’s say they are Q and C, and all of the descendants will carry the mitochondrial haplogroups of the females – let’s say A, B, C, D and X.
There is a very limited amount of autosomal DNA to pass around. If all of those 10 people are entirely unrelated, which is virtually impossible, there will be only 10 possible combinations of DNA to be selected from. Within a few generations, everyone will carry part of those 10 ancestor’s DNA. We all have 8 ancestors at the great-grandparent level. By the time those original settlers’ descendants had great-great-grandparents – of which each one had 16, at least 6 of those original people would be repeated twice in their tree.
There was only so much DNA to be passed around. In time, some of the segments would no longer be able to be recombined because when you look at phasing, the parents DNA was exactly the same, example below. This is what happens in endogamous populations.
|My Result||My Result||Mother’s Result||Mother’s Result||Father’s Result||Father’s Result|
Let’s say this group’s descendants lived without contact with other groups, for maybe 15,000 years in their new country. That same DNA is still being passed around and around because there was no source for new DNA. Mutations did occur from time to time, and those were also passed on, of course, but that was the only source of changed DNA – until they had contact with a new population.
When they had contact with a new population and admixture occurred, the normal 50% recombination/washout in every generation began – but for the previous 15,000 years, there had been no 50% shift because the DNA of the population was, in essence, all the same. A study about the Ashkenazi Jews that suggests they had only a founding population of about 350 people 700 years ago was released this week – explaining why Ashkenazi Jewish descendants have thousands of autosomal matches and match almost everyone else who is Ashkenazi. I hope that eventually scientists will do this same kind of study with Anzick and Native Americans.
If the “new population” we’ve been discussing was Native Americans, their males 15,000 year later would still carry haplogroups Q and C and the mitochondrial DNA would still be A, B, C, D and X. Those haplogroups, and subgroups formed from mutations that occurred in their descendants, would come to define their population group.
In some cases, today, Anzick matches people who have virtually no non-Native admixture at the same level as if they were just a few generations removed, shown on the chart below.
Since, in essence, these people still haven’t admixed with a new population group, those same ancient DNA segments are being passed around intact, which tells us how incredibly inbred this original small population must have been. This is known as a genetic bottleneck.
The admixture report below is for the first individual on the Anzick one to all Gedmatch compare at 700 SNPs and 7cM, above. In essence, this currently living non-admixed individual still hasn’t met that new population group.
If this “new population” group was Neanderthal, perhaps they lived in small groups for tens of thousands of years, until they met people exiting Africa, or Denisovans, and admixed with them.
There weren’t a lot of people anyplace on the globe, so by virtue of necessity, everyone lived in small population groups. Looking at the odds of survival, it’s amazing that any of us are here today.
But, we are, and we carry the remains, the remnants of those precious ancestors, the Denisovans, the Neanderthals and Anzick. Through their DNA, and ours, we reach back tens of thousands of years on the human migration path. Their journey is also our journey. It’s absolutely amazing and it’s no wonder people have so many questions and such a sense of enchantment. But it’s true – and only you can determine exactly what this means to you.
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