Pedigree Collapse – “The common historical tendency to marry those within walking distance, due to the relative immobility of the population before modern transport, meant that most marriage partners were at least distantly related. Even in America around the 19th century, the tendency of immigrants to marry among their ethnic, language or cultural group produced many cousin marriages.” International Society of Genetic Genealogy Wiki – https://isogg.org/wiki/Pedigree_collapse viewed 10 June 2021.
Endogamy – “the practice of marrying within the same ethnic, cultural, social, religious or tribal group. In endogamous populations everyone will descend from the same small gene pool. People will be related to each other in a recent genealogical time-frame on multiple ancestral pathways and the same ancestors will, therefore, appear in many different places on their pedigree chart.” International Society of Genetic Genealogy Wiki – “https://isogg.org/wiki/Endogamy” viewed 10 June 2021
When I look at the autosomnal DNA matches on Ancestry or MyHeritage that appear to be through my Swartz/Prather 3rd great grandparents, there are often multiple possible pathways of relationship for most of my matches. And it is quite common for the projected relationship of these matches to be closer than the actual relationship – because the amount of shared DNA seems to be too high for the actual relationship as shown via documentation. Pedigree collapse? Endogamy? Odd DNA inheritance pattern?
My 3rd great grandparents John Swartz/Schwartz and Nancy Prather met, married (1814) and raised their family (1815 – 1827) in early Clark County, Indiana. They came from different ethnic backgrounds. They had moved far from their place of birth – John from Pennsylvania and Nancy from North Carolina before they married. And the early Clark County community was regularly enriched by new immigrants through at least the 1880s. This would seem to rule out both Pedigree Collapse and Endogomy.
However, the Swartz/Schwartz and Prather families are thick on the ground in Clark County, Indiana – even today. And those two 3rd great grandparents weren’t only children – far from it. John Swartz was one of 10 known children and Nancy Prather was one of 13 (although she was the only child of that particular marriage. All 12 of her siblings are from her father’s second marriage.) And of those 23 combined siblings only 2 or 3 moved out of the area. So there were dozens if not hundreds of descendants of those siblings living in Clark County by 1850 and guess what……they intermarried or they intermarried with the siblings of the partners of their siblings and cousins. Which sounds like the chorus of a Gilbert and Sullivan operetta.
I did a quick and dirty study of the intermarriages (within the first 2 generations) of the children of 3 of Nancy’s siblings and 4 of John’s. The surnames that dominate, in descending order are Prather, Swartz/Schwartz, Lentz, Crum, Jacobs, Botttorff, Fry and Holman (I suspect the Smith family will come heavily into the equation once I finish all of the work on John’s sister Mary Anne Swartz Smith. However, Smith being the common name it is……) Within 2 generations there are 66 marriages between these surnames. The Prathers married the Prathers as well as all of the others. The Swartzs did not marry Swartz surnamed cousins but they married plenty of cousins with other surnames. Both families started their history in Clark County with just one founding family – but the Prather family was composed of a single couple and their adult or nearly adult children and the Swartz family was a single couple with young children. So John was the oldest son of the founding couple and Nancy was the oldest grandchild of the Prather founding couple.
I think, what I have here is a classic case of hidden recent Pedigree Collapse. Clark County, Indiana was frontier country when my ancestors moved there, even though it was the 19th century (just barely). And the pool of potential marriage partners was fairly restricted for about 20-30 years. Quite long enough to establish the practice of marrying your cousin. And certainly long enough to create havoc with my DNA match pathways. Now I need to think about Endogamy in the German Russia population – both in Russia and in the US.