Not all endogamy is the same

Kitty Cooper’s recent blog post “using Ashkenazi Jewish DNA to find family” talks about how to look for key signs when it comes to finding a true connection to your matches.  I recently blogged about the problems with Polynesian matches and endogamy, just as Ashkenazi Jews will encounter.  I had two different blog entries.  One was “ADSA and Triangulation” where triangulation is used to possibly figure out if you and two other matches can help each other figuring out your common ancestor.  And “Endogamy and Multiple Smaller Segments” where I discovered the actual problem with Polynesian DNA and finding matches.

In Kitty’s entry, she did give tips for finding real AJ matches. Whenever people talk about endogamy, they always bring up AJ as the most prominent group, but the fact is any endogamous group will have its own peculiarity.  I noticed that with Colonial families they have to have what they refer to as “sticky segments”, or segments on a chromosome that basically lingers on for awhile, generation after generation.  I have seen how these segments can begin and end at exactly the same start/end points, which is very interesting.

AJ come from a founding population that started with a small number of people.  Many other endogamous groups started in the same fashion for the most part, particularly colonial families.  With colonial families and Acadians of French Canada, you can see the constant intermarrying within families generation after generation.

DNA Research says that Polynesians slowly moved eastward creating these series of founder effects.  By the time they reached central eastern Polynesia, they were getting genetically less diverse.  They thrived for centuries developing their culture, and then more emigration occurred to the farthest parts of the Polynesian triangle.  The Maoris (New Zealand), Hawaiians and Rapa Nui people (Easter Island) are expected to be a subset of the genetic variability in eastern Polynesia, which in turn is expected to be a subset from western Polynesia, which itself is a subset of Melanesia.  A series of founder effects is what lead to this low genetic diversity.

Whenever people talk about endogamy and use AJ as an example when it comes to calculating relationships, or even reading what Kitty Cooper wrote for tips in working with AJ DNA, I keep reminding people that not all endogamous groups are the same, such as the case with Polynesian DNA.  So as Polynesians moved from the west towards the east, and then finally to the most farthest corners of the Polynesian triangle, where Hawaii is at its vertex angle, New Zealand and Easter Island at its base angles, genetic diversity diminishes.

Bottleneck is another feature enhancing the degree of endogamy with Polynesians.  There may have been several bottleneck effects that took place among various island group of Polynesia.  For Hawaii, the last known bottleneck occurred in the late 19th century.  When Captain Cook, a British arrived in the Hawaiian islands in 1778, he estimated the population to be around 300,000.  Scholars will mention anywhere from 800,000 to nearly a million in the islands at the time of European contact.  The 1890 Hawaiian Kingdom census counted 40,622 aboriginal Hawaiians.  The 2000 US Census had counted 401,000 Native Hawaiians.  So the current Kanaka (Native Hawaiian) population comes from the 40,622 that existed 124 years ago.

When thinking about the lack of genetic diversity given the entire history, it should not be surprising that, as in my case being Hawaiian, that not only will I have many close matches with other Hawaiians, but with other Polynesians too.  More specifically what we have been seeing, is a close genetic relationship with the Maoris.  That is understandable since both of our groups were the last places to be colonized by Polynesians.

So what does that mean for Polynesians working on their DNA matches?  It is okay to read about other methods that endogamous groups use to find their matches, but be aware that we have much closer matches unlike other groups.  If you are on FTDNA, you will find a lot of 1st – 3rd and 2nd – 3rd cousin matches.  I get 3 pages of 2nd – 3rd cousin matches while my mother has about a page and a half of 1st – 2nd cousins, just over two pages of 1st – 3rd cousin and five pages of 2nd – 3rd cousin matches.  At 23andme, I get 2nd cousins, and 2nd – 3rd cousins and two pages of 2nd – 4th cousins.  This is what to be expected, and again a true closer relationship will be distinguishable by looking at the number of segments.  We may share a lot when it comes to total centimorgans in order to get 2nd – 3rd cousins, but a real 2nd to 3rd cousin match should not have as many segments and these multiple segments will average anywhere between 8cM – 15cM.  This means that the match is endogamous.

When doing triangulations you will see that with your matches there is a fair amount of shared segments with other people of whom will share that matching segment.  With non-endogamous groups, you need to first verify that both of your matches are sharing that same segment with each other in order to determine that you all have a common ancestor.  For Polynesians, this is often the case, and probably descended multiple times from that same ancestor.  That may seem significant and on the right path for finding a connection however its extremely low genetic diversity coupled with the fact that many records did not exist until recently usually produces no results.

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