Do DNA results support theory of 1860s adoption of illegitimate nephew?

Question

I suspect that George Kober, born 12 Feb 1858 at New Haven, CT, was the illegitimate son of Mary Agnes Kober, born 27 July 1839 at Liebelsburg, Calw, Germany. I also suspect that he was adopted by Mary's brother, Elias and his wife around 1860 in New Haven. Mary and Elias were part of a large Kober family who chain-immigrated from Germany to CT in the 1850s. Here is the paper trail:

1. Elias Kober and his wife (also named Mary) have a son named George Frederick Kober, 31 Jan 1859, New Haven.
2. This son George Frederick died 1 July 1860 of dysentery.
3. The 7 Aug 1860 US census has Elias Kober, wife and young son George (age 1) in Ward 3, New Haven. Cannot find the sister Mary in this census.
4. Mary Kober died at New Haven of "brain fever", 25 March 1862, age 22 years 7 months.
5. 28 March 1862 - Elias KOBER is appointed the administrator of Mary’s estate, and he is identified as "a brother".

I suspect that the "estate" of Mary Kober, a 22-year-old unmarried immigrant woman, was probably her son George, and that this court document was a means of legitimizing what was an informal adoption of this George by her brother Elias. He appears to have already been living with Elias at the time of the 1860 census.

However, as unlikely as it sounds, it is still possible that Elias & his wife scooped up a random street urchin to adopt in their despair after the death of their son George Frederick. Enter autosomal DNA results.

Elias and his wife had another son, Frederick Kober, born 9 Aug 1862. A paper-trail descendant of Frederick and a paper-trail descendant of George recently did autosomal DNA tests at a major genealogy company. These two descendants share 20cM, which is not a lot, but it suggests that George and Frederick are genetically related.

On paper, these two individuals are either full 3rd cousins, or full 4th cousins, depending on whether George and Frederick were full brothers, or 1st cousins. Using the Shared cM tool from DNA Painter, their relationship has an 8% chance of being 3rd cousins, and a 16% chance of being 4th cousins.

Do these DNA results support the paper trail that George Kober, raised by Elias Kober & wife as a son, was actually their nephew and child of sister Mary Kober or is it too small of a match to be significant?

Answer 1

You don't say how many segments your 20 cM match is, but it's significant. A 20 cM single-segment match effectively guarantees a common ancestor, but doesn't indicate along which ancestral line, or how far back. The more segments there are in your 20 cM, the less likely the match is significant.

You'll need a lot more than one pair-wise sample to make a case like this - you'll need multiple samples, all with good paper trails (for all ancestral lines), and who match each other (triangulation would be favorite). I'm not sure of the math for how many samples would make up a statistically significant set, but offhand I'd guess at least 3-4 in each line (George & Frederick).

That done, you'd still need to prove that George wasn't Elias' biological son. The key there is that descendants of Frederick should see matches (albeit distantly) with descendants of the family of Elias' wife Mary, which presumes that you know her maiden name, and enough of her family to be able to trace descendants of her siblings. If your hypothesis about George is correct, then descendants of George would likely not share any of those matches, unless George's biological father was closely related to Elias' wife (a possibility).

Answer 2

I find this interesting that I randomly did a search for Kober, and this pops up. I AM a direct descendant of Elias KOBER and his wife Mary Agnes Wellhauser. Elias and Mary and my 3rd great-grandparents. My maternal grandfather is buried in their family plot. I also have located both Elias’s sisters grave as well as Elias and Mary’s first son George, who passed from dysentery. They are both in the Grove Street Cemetery, downtown New Haven, CT.

Both my mother, myself, and her first cousin have done DNA testing. Please reach out to me! Photo is of Elias from my family photo album