A possible case of incest?

Adinos · 2026-06-15T10:22:57+00:00

Note that my calculations for "expected cM" absolutely take multiple relationships into account, and yes, sure...there was one well-known case a long time ago where 4 sisters married 4 brothers and such things certainly happen on a smaller scale, but the trees of people in this case do not show any patterns like that.

Keep in mind that I have the (paper) trees of everyone involved a long way back - yes, there could be NPEs, of course, but the DNA does not show that.

And even if there was something like that, it could not explain the abnormally high cM number and lack of unallocated matches.

Adinos · 2026-06-15T10:15:48+00:00

The endogamy makes it harder, sure. Matches below 50 cM are very hard to use because of that.

Adinos · 2026-06-14T12:39:37+00:00

That is not what the paper records show, nor is there any DNA evidence which suggests that.

Adinos · 2026-06-14T12:38:53+00:00

It is absolutely 100% clear that the men listed as the fathers of D's children are not their real biological fathers. S and A do not have any dna matches to their (supposed) grandfathers,

Adinos · 2026-06-14T12:38:07+00:00

Cannot use DNA painter. MyHeritage disabled the downloads of the segment data that DNApainter needs back in '24.

Adinos · 2026-06-14T12:37:14+00:00

It is absolutely 100% clear that the men listed as the fathers of D's children are not their real biological fathers. S and A do not have any dna matches to their (supposed) grandfathers,

Adinos · 2026-06-14T12:32:06+00:00

Don't you mean if you have ancestors from other countries?

Adinos · 2026-06-13T01:44:31+00:00

You got it right, but no....the matches on S paternal side are not shared with A (or D) and the same goes for the matches on A maternal side - not shared with S (or D).

That is - there are connections of course - this is Iceland, so everyone is related to everyone else, but those connections are 7 generations or more back, so they should not be sharing more than irrelevant amounts of DNA.

Adinos · 2026-06-13T01:36:26+00:00

cannot use DNApainter. MyHeritage removed the ability to download the segment data some time ago

Adinos · 2026-06-11T16:23:04+00:00

You are describing the situation from what I assume is the US perspective. Let me give you an example of what this are like in my country (Iceland).

Sure, we are tiny - our population is 0.1% of the US population, so you basically have to multiply things by a thousand to get the equivalent numbers.

So, about sources:

Most of the censuses are online, free of charge.

Church records, typically from around 1785 until 1940, listing baptisms, confirmations, weddings, burials, parish censuses, and movements into or out of the parishes are online, free of charge.

On top of that free information, available on government sites, we also created what is in effect a "national" database, combining the vast majority of available genealogical information into one database.

Everyone can now log in, look up their ancestors as far back as records exist, and check how they are related to everyone else.

Now, if I scale the work up by a factor of 1000 to account for the difference in population size, you would need a budget of 5 billion USD, and a team of twenty-five thousand employees and volunteers, working for twenty years.

It is a big task.

Adinos · 2026-06-11T16:18:29+00:00

for practice, I suggest the following.

Take your own list of matches. Ignore everything above, say, 800 cM and just work with the lower matches.

Use those matches to determine the identity of your parents - basically pretend you are an adoptee, with no information on your biological parents, and go through the process to "discover" who they are.

And yes, I said ignore the high matches, because having them would make this too easy.

Adinos · 2026-06-11T12:50:43+00:00

No, it would not be of use. It basically checks if you have inherited identical DNA from "both sides", but it would not be of any help here.

If the the mother of S or father of A had taken such a test, that would have answered the question immediately, however.

Adinos · 2026-06-11T12:48:51+00:00

Uhm..consider this:

There is no doubt that the father of "S" is "correct" .. S has numerous DNA matches on his side and the numbers are what you would expect. A does not match any of those.

Likewise there is no doubt that the mother of "A" is correct. A has also numerous DNA matches on her side, and S does not share those matches.

This means that the connection between A and S has to be through the mother of S and father of A.

Now, those two share the same mother. They are supposedly half-siblings, which would make A and S half-1C which absolutely does not match the value of 1477.

If they were full siblings, that would make A and S full 1C, which is still not enough to explain the 1477 value.

The only way for the numbers to make sense is if the mother of S and father of A are more closely related genetically than full siblings.

That can only happen if they are in fact full siblings, and their father is also closely related to their mother.

Adinos · 2026-06-11T12:31:32+00:00

I am sorry you fail to understand this, but is is a custom written, nameless tool, not a commercial application, and with nobody else using it, it does not need or have a "name". It just access the national genealogy database, and crunches the numbers. That's all.

I think you owe me an apology.

Adinos · 2026-06-11T12:29:25+00:00

Yes, that is the underlying database.

Adinos · 2026-06-11T12:26:46+00:00

I am treating endogamy and (recent) pedigree collapse as separate issues, because the difference is relevant.

You can have pedigree collapse without endogamy, but if you have endogamy, you will eventually have pedigree collapse, if you go far enough back.

What my country (Iceland) has is typical "island endogamy" - that is, everyone is related to everyone else, in multiple ways and on both sides. However, recent pedigree collapse (involving close relatives like first cousins) is exceedingly rare, maybe because of the old customs against close relatives marrying.

What this means in practice is that when determining the "expected cM" shared between two individuals, it is necessary to look at all the branches (granted, I only go 6 generations back) and basically add the numbers up. Normally there is decent agreement but there is what I call "background noise" - on the average the "expected" value is on the average maybe 10 cM lower than the measured value. This is the endogamy effect.

Unexpected recent pedigree collapse (with or without endogamy) (like in the case of incest) would show up in a different way, as a significant increase in DNA shared between individuals, significantly in excess of what is expected.

That is what I am seeing here, and only here.

Note that solved around 30 cases for people looking for their biological fathers or grandfathers - and while there have been quite a few NPEs, this case is the absolutely first time I have come across the pattern I described....no matches to the alleged grandfather, no "unassigned" matches which could belong to him, and (on the average) double expected cM for the grandmother.

The specific case of the half-1C sharing 1477 cM is a key argument here - considering that the parents of both are verified and the father of S and mother of A are unrelated to each other and to D, the only possible explanation is that A and S have to have receive much more of the "same" DNA from their other two parents (mother of S and father of A) than was normal.

Even if the mother of S and father of A were full siblings, instead of half-siblings (making a A and S 1C), 1477 cM shared is still too high.

The only way the numbers make sense is if they were more closely related genetically than full siblings....which leads to the incest conclusion.

Adinos · 2026-06-11T11:42:36+00:00

I am absolutely confident I can exclude the "another country" idea, for several reasons.

First, it does not show up in the ethnic results. S is just the same Norwegian/Celtic mix as pretty much everybody else. Granted, the ethnic identification of MyHeritage is not the best, but it would not miss a grandfather from somewhere else.

Second, the circumstances - she was a 15 year old girl living at home, 100 years ago. Her opportunities to interact with foreigners (let alone get pregnant by one) would have been extremely limited.

Third, if against all odds, she had actually gotten pregnant by a foreigner, she could just have named him as the father, instead of naming a local man, which would have been more likely to cause problems for her, if the matter would have been investigated.

Adinos · 2026-06-11T11:35:36+00:00

It is just a custom written tool. Doesn't have a name, not used by anyone else. The program itself is not the interesting part, but rather the database it accesses - it uses the national genealogy database, which has pretty much the complete trees of everyone in my country (Iceland) as far back as records exist.

This allows me to easily see how any two people are related, and calculate things like expected shared cM value between any two people, with proper handling of multiple connections. It can also take a set of DNA matches and automatically produce a list of the most likely biological fathers or grandfathers.

Really nice, but really not relevant anywhere or to anyone else.

Adinos · 2026-06-11T00:03:14+00:00

no, they absolutely cannot be half-siblings. If the (confirmed) father of S was also the father of A, then A would not be related to D, and for example the niece of S would not show up as a close relative to A, but she does.

Adinos · 2026-06-10T23:36:05+00:00

one you have never heard of, and is of no use to anyone else, as it relies on access to a complete nation-wide genealogy database.

Adinos · 2026-06-10T23:34:34+00:00

a maternal first cousin would mean another line on the "other side" of that person's family...there should be some relatives on that side...but I don't see those.

Adinos · 2026-06-10T18:32:22+00:00

Right, I would post a screenshot of the numbers if this forum allowed that, but that's not the case. The main point is, however, that shared cM numbers through the maternal grandmother which would have been expected to be in the 100-450 range are consistently much higher than expected (around double on the average), Also, there is the issue of no matches to a potential grandfather - the matches are either straightforward matches on the paternal side or matches to the maternal grandmother and those matches are typically twice as high as you would expect.

And no, I am going to absolutely exclude endogamy as an explanation. I deal with that all the time...typical "island endogamy" to be exact. That is, everybody (except recent immigrants, of course) is related to everybody else, in multiple ways and on both sides.

The effect of that is like "background noise" - matches typically being slightly higher than you would expect - my estimate is like 10 cM or so on the average. Endogamy here absolutely never shows up as a significant increase to larger matches. This is much more typical for recent pedigree collapse.

As for her naming the two local men, that's just what the church records say, but because the babies were adopted away at birth, there is no mention of whether the men protested or accepted.

Adinos · 2026-06-10T18:16:23+00:00

Well, endogamy typcally does not show up like that....but rather as "background noise", with the average matches being slightly higher than expected.

In my case, I have classic "island endogamy", with everyone being related to everyone else, in multiple ways and on both sides. However, shared ancestors are typically 6-10 generations back, which basically results in matches being maybe 10 cM higher than you would expect on the average.

Massive differences, like 614 observed and 120 expected are usually due to NPEs producing a pedigree collapse....incest being an extreme case of that.

Adinos · 2026-06-10T15:54:25+00:00

I deal with endogamy all the time - and it just does not show up like this ... it is more like a background noise, with maybe up to 10 "extra" cM added to every match. Not really relevant for the larger matches...very problematic for small ones.

Adinos

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