Recent Founder’s Effect, bottlenecking and 6 Tahitian women on Pitcairn island

I finally got the autosomal results of a Pitcairn resident who has been a member of the Polynesian project for a year now.  Previously I had another member who is a Norfolk island descendant and whose ancestors moved to Norfolk but were originally from Pitcairn.  Another Norfolk descendant tested at another company, but his raw data were uploaded to GEDmatch.com in order to be compared.  Now having that this particular Pitcairn resident tested, I can make a comparison for these 3 people since they all have ties to Pitcairn.

 

HISTORY OF PITCAIRN ISLAND

Pitcairn was settled in 1790 by mutineers of the HMS Bounty and Tahitians¹.  The initial population of 27 consisted of 9 mutineers, 6 Tahitian men and 11 Tahitian women along with an infant girl.  Only 6 of the mutineers and 6 Tahitian women would produce descendants.

Mutineers:
1) Fletcher Christian
2) Edward Ned Young
3) John Mills
4) William McCoy
5) Matthew Quintal
6) John Adams

Tahitian women:
1) Mauatua Maimiti
2) Teraura
3) Teio
4) Tevarua²
5) Vahineatua
6) Toofaiti

 

POPULATION GROWTH, DECREASE & RE-POPULATION

The population started with 27 people but only 12 of them would produce descendants.  By 1840 the population exceeded 100, and by the mid-1850s the community was outgrowing the island³.

On May 3, 1850 the entire community left for a 5 week trip and settled on the island of Norfolk on June 8.  Nearly 3 years later 16 of them returned to Pitcairn.

 

EFFECTS WITH AUTOSOMAL DNA

I have mentioned in previous blog entries that eastern Polynesians are genetically less diverse than western Polynesians.  So it should be no surprise that Hawaiians and Maoris as well as Tahitians will come up as closer matches to each other despite sharing common ancestors 8 centuries ago.

Now we are looking at two things.  Firstly, a founding population where only 12 people produced offspring, and half of the 12 being Tahitian women, or eastern Polynesians.  And these 12 were not paired off equally.

They married multiple times, some of them never produced descendants with their other spouses.

Secondly, there was a population bottleneck in 1859.

In 1856 the population expanded to 193, then the entire population left.  That population was already interrelated just 66 years after the initial 12 founding people started the population.  They all left, but 16 of them returned.  Eventually, a few more returned but the remaining population continued life on Norfolk island while the rest of the Pitcairns were starting the population again. It would take only 23 years to repopulate the island increasing the population to 250.

 

ANALYZING A PITCAIRN RESIDENT’S AUTOSOMAL DNA

The Pitcairn resident descends from all of the 12 founding people.  No surprise, given that small amount plus that was just 225 years ago and 7 generations ago for this particular person.

Although I cannot show with a family tree how many times they descend from the 12 founding people due to size and the complexity of the tree, I decided to list the number of times they descend from each of the 12.

This resident’s paternal grandparents are 2nd cousins one way, and 3rd cousins another way while their maternal grandparents were 2nd cousins two ways.  There are more ways that they are related going further back as well, but my genealogy software cannot pick up the multiple relationships and it seems to select the closest relationship but selected 2nd cousin once removed, so not sure which line it was picking up.  This person’s maternal grandfather was born on Pitcairn but there is no known genealogy for him.  For their other grandparents, here is who they descend from.  (Founding people in bold)

Paternal grandfather – Christopher Warren, son of George Warren whose mother was Agnes Christian, and Alice Butler whose mother was Alice McCoy.
Paternal grandmother – Mary Christian, daughter of Sidney Christian & Ethel Young.
Maternal grandmother – Ivy Young, daughter of William Young & Mercy Young.

Agnes Christian and Alice McCoy were 2nd cousins, great-granddaughters of Fletcher Christian and Mauatua.  Ivy Young’s parents William and Mercy Young were 2nd cousins two ways to each other.  Great-grandchildren of Edward N. Young and Toofaiti and of Fletcher Christian and Mauatua.

As confusing as it seems, you can imagine how would DNA show up.  After uploading the raw data to GEDmatch.com for further analysis, I immediately ran the “Are Your Parents Related” tool.

It predicted 3.3 for the most recent common ancestor (MRCA).  Still not sure how to interpret GEDmatch’s MRCA estimation, but in reality, the most recent common ancestor would be their 2nd great-grandparents – Thursday October Christian II and Mary Polly Young.  And there were other Youngs as I previously mentioned and Christians as well.

When I ran my mother’s kit through that same tool, her largest segment was 13.9cM, and there were a total of 5 segments that would total 51.5cM.

Largest segment = 13.9 cM
Total of segments > 7 cM = 51.5 cM
Estimated number of generations to MRCA = 4.1

Unlike the Pitcairn resident whose largest segment was 24.7cM and with 11 segments.  My mother’s parents were from different islands and as far back as I was able to trace their ancestries, they did not intersect nor did their ancestors come remotely near to each other given that they were from 3 different islands.

I would love to get more Pitcairn residents to test, to see if there is any noticeable pattern using this tool, or David Pike’s ROH.  If there is, we definitely could use it in helping to determine a true close genetic match versus an endogamous one.

 

COMPARING TO NORFOLK DESCENDANTS

There are 2 particular matches to many of the Polynesian DNA project’s members and both of these 2 people are descendants of Norfolk residents.  I will refer to them as Norfolk #1 and Norfolk #2.

Norfolk #1’s maternal grandmother was from Norfolk and she was the daughter of Francis Nobbs and Ruth Christian.  Norfolk #2’s maternal grandfather was from there, and his parents were William Adams and Sarah Christian.

A further breakdown where I bold the founding people.

NORFOLK #1
Francis Nobbs’ ancestry, son of Alfred Nobbs & Mary Christian:
Paternal grandfather – George Nobbs
Paternal grandmother – Sarah Christian, daughter of Charles Christian & Tevarua
Maternal grandfather – Benjamin Christian, son of John Buffett & Mary Christian
Maternal grandmother – Eliza Quintal, daughter of John Quintal & Maria Christian

Sarah and Maria Christian were daughters of Charles Christian & Tevarua, while Mary Christian was their 1st cousin.

Ruth Christian’s ancestry, daughter of Isaac Christian & Miriam Young:
Paternal grandfather – Charles Christian, son of Fletcher Christian & Mauatua
Paternal grandmother – Tevarua, daughter of Teio
Maternal grandfather – William Young, son of Edward N. Young & Toofaiti
Maternal grandmother – Elizabeth Mills, daughter of John Mills & Vahineatua

NORFOLK #2
William Adams’ ancestry, son of John Adams & Caroline Quintal:
Paternal grandfather – George Adams, son of John Adams & Teio
Paternal grandmother – Polly Young, daughter of Edward N. Young & Toofaiti
Maternal grandfather – Arthur Quintal, son of Matthew Quintal & Tevarua
Maternal grandmother – Catherine McCoy, daughter of William McCoy & Teio

When comparing the two Norfolk descendants to the Pitcairn resident, I was surprised to see no overlapping segments.

It is interesting to see how for Norfolk #1, the largest segment is 40.85cM for the largest segment and a total of 134.5cM.  The largest segment is significant, and although Pitcairn & Norfolk #1 are related multiple ways, the closest known relationship makes them 4th cousin once removed.

Comparing Pitcairn to Norfolk #2, the largest segment is 27.3cM, which for Polynesians in general could be pretty distant.  Total shared is 95.1cM.  And just as with Norfolk #1, Norfolk #2 and Pitcairn are related multiple ways, but the closest relationship makes them 4th cousins.

At the moment I cannot compare Norfolk #1 and Norfolk #2, but I am trying to get one that taken care of in order to upload Norfolk #1’s raw data to GEDmatch for further analysis.

I was expecting to see the overlap at least when comparing to the Pitcairn resident given that their ancestors’ have been on the island since the beginning, but it goes to show how unpredictable and random DNA can be.

A list of all 3 and how many times they each descend from the following founding population.

And while various Polynesians can be compared to all three of these people and may show overlapping segments, there is really no way to map these segments.  These 3 testees would match other project members based on segments inherited by one or more of these 6 Tahitian women that settled on Pitcairn.  And we all would have shared common ancestor(s) from at least 8 centuries ago.

Below I compare the Pitcairn resident to a Hawaiian, a Maori and a Cook Island Maori as well as my Hawaiian mother.  Incidentally, there is a project member whose father was from Tahiti, yet that person does not come up as a match.

(default setting)

(1+cM setting)

 

Comparing Norfolk #1 with the same people with the exception of not being a match to the Cook Island Maori.

(default setting)

(1+cM setting)

Norfolk #2 did not test at FTDNA but at 23andme, and although their raw data was uploaded to GEDmatch.com, all the others being compared were not uploaded except for my mother’s raw data.

For additional information about the DNA study of the descendants of the Mutiny on the Bounty, see ‘Mutiny on the Bounty’: the genetic history of Norfolk Island reveals extreme gender-biased admixture.

Footnotes

1. History of the Pitcairn Islands.
2. Pitcairn Settlers lists an additional Tahitian woman known as Sully, as the wife of Matthew Quintal and the mother of Matthew Jr., John, Arthur, Sarah and Jane Quintal. Another source, as well as the Pitcairn resident who got DNA tested, claims that there were only 6 Tahitian women of whom they descend from.  There was no mention of Sully, although Tevarua is listed as being married to Matthew Quintal and the parents of  Matthew Jr., John, Arthur, Sarah, and Jane Quintal.
3. Historical Population of Pitcairn.