Unless you are a seasoned genealogist, you may have never heard the terms Pedigree Collapse or Endogamy. These terms are used in relation to your family tree.
Upon building your family tree, you double the size of your tree for each generation: you have 2 parents, 4 grandparents, 8 great grandparents, 16 2nd-great grandparents, 32 3rd-great grandparents and so on. When you think about it, that is a whole lot of people to research when you go too far back, especially once you add other children to each set of grandparents.
At WarBabies, we focus within the first 3 generations of you, as seen in the chart to the right. What this means is we primarily focus on who your DNA matches are up to your 2nd cousins. If your closest matches are 3rd cousins, this makes our research timely and more challenging. If your closest DNA matches are 4th cousin or farther out, it makes it darn near impossible to find your close family because of pedigree collapse and endogamy.
In genealogy, pedigree collapse describes how reproduction between two individuals who knowingly or unknowingly share an ancestor (endogamy) causes the family tree of their offspring to be smaller than it would otherwise be.
Endogamy is the practice of marrying within a specific social group, or ethnic group, rejecting those from others as unsuitable for marriage or other close personal relationships. Endogamy is also the term for when cousins marry cousins, whether it be knowingly or unknown to each party.
Endogamy is common in many cultures and ethnic groups. Several religious and ethnic religious groups are traditionally more endoganous. Endogamy, as distinct from consanguinity (the fact of being descended from the same ancestor), may result in transmission of genetic disorders, the so-called founder effect, within the relatively closed community.
By building a family tree, after reaching a later generations, you may discover several lines that intertwine due to a relationship between cousins or similar family. What this does is "collapse" the pedigree of your tree, shortening it because these lines are duplicated.
You must remember, this was a VERY common practice prior to the 1900's when our ancestors didn't have easy modes of transportation and "stuck to their own kind" in their small towns and villages. The dating pool was much smaller and in order to survive, it was acceptable to marry and have children with a cousin, sometimes even with aunts/uncles marrying their nieces/nephews.
In today's society, this practice is highly looked down upon, and may even be illegal in some states. However, it is still common in many different cultures outside of the United States.