When Ancestry ThruLines™ gets it Wrong

 ThruLines is a marvellous tool for sorting out your more distant DNA connections, but it depends on the majority of people having accurate trees on ancestry (see "Getting the best out of an autosomal DNA test"). When there are a substantial number of inaccurate trees for a family ThruLines can be led astray.

In January 2021 I found a AncestryDNA^© Match with a suggested ThruLines link¹:

You and [DNA Match]
< 1% shared DNA | 6 cM across 1 segments
Unweighted shared DNA: 6 cM
Longest segment: 6 cM

Shortly after this Matches with such low cM values were cut from the results unless you had marked or noted them in some way. It was also relatively early days for ThruLines.

Figure 1 shows the relationship suggested by ThruLines with John Wickham (1737-1825) and Mary Baldwyn (1736-1825) as our Most Recent Common Ancestors (MRCAs).

Figure 1: The genetic link as proposed by ThruLines.

The late marriage is not unusual, but for a premarital child of a couple to keep their mother’s surname is. It usually indicates that the child is not the offspring of the groom. Also the middle name ‘Field’ is unexpected if the father is John Wickham.

Looking at Poor Law records:

East Sussex Bastardy Orders: Mayfield:
“1829 Dec 4 Maintenance order on Joseph FIELD, labourer tp for a bastard son of Phoebe DANN born 2 Jan 1828 (Par.422/34/2/127)
[Phoebe DANN married 27 June 1835 at Mayfield, John WICKHAM, widower].
Alfred Field son of Phoebe DANN, spinster, baptised 8 February 1829.”²

So according to Phoebe, Alfred Field Dann is her son by Joseph Field, which at least explains the middle name. But where does the Wickham link come from? Is it via Joseph Field or Phoebe Dann? It turns out there is a link via Phoebe herself³.

Phoebe Dann is the daughter of Thomas Dann and Jane Hobbs. Jane Hobbs is the daughter of William Hobbs and Elizabeth WICKHAM. Elizabeth Wickham is the daughter of Richard Wickham and Ann Colchin. She is also the sister of John Wickham, father of my 3xgreat-grandmother, Ruth Wickham, and grandfather of Phoebe's husband John Wickham, who is thus a second cousin of Phoebe Dann as well as her husband. So the MRCAs for my DNA Match and myself are (in the absence of any other link) Richard Wickham and Ann Colchin, and the DNA match and I are seventh cousins. Figure 2 shows the actual relationship.

Figure 2: An actual genetic link

I now have this information in my Ancestry tree, but the DNA Match does not appear as a ThruLine any more as it is eight generations back. I don’t mind, I value accuracy above ease.

This sort of multiple relationship can make sorting out DNA links complicated. Because of Phoebe’s Wickham ancestry, it would be easy to assume that all her children were fathered by her eventual husband, John Wickham. However any descendant of Phoebe Dann would show a Wickham link, as shown by the DNA Match of mine descended from Alfred Dann. Statistically though descendants of Phoebe by John Wickham would have the chance of a double dose of Wickham/Colchin DNA and average twice the amount of shared DNA compared to the descendants of Phoebe alone. The suggested link still appears on ThruLines for other DNA matches of mine who are descendants of Alfred Field Dann, hence the use of this example in a blog post.

Multiple marriages can also cause confusion, particularly for husbands who favour a particular given name in their wives. Another DNA match of mine traces their ancestry back to Jane Knight (1824-1904, daughter of Richard and Elizabeth Knight)¹. In their tree they identify Elizabeth Knight with Elizabeth Rolph (1810-1855, married Richard Knight in 1830) and our MRCAs to be William Rolph (1787-1860) and Sarah Borders (1789-1869). (This match is part of a large genetic network of Rolph/Borders descendants.) However this identification would make Elizabeth Rolph only 14 years old when Jane was born (and occurs six years before the Knight-Rolph marriage). Of course the answer is that Richard Knight had a previous marriage (to Elizabeth Stapleton (1799-1828) and Jane is the child of this marriage. Jane cannot then carry the Rolph/Borders genes, so where is the link?

Looking at the family tree we find that Jane Knight's son, Daniel Filler (1851-1928) married Phoebe Philpott (1853-1902). Phoebe Philpott is the daughter of Eliza Knight (1832-1914), the granddaughter of Elizabeth Rolph (1810-1855) and thus half-cousin of Daniel Filler. So it is Eliza Knight (half sister of Jane Knight) who carries the Rolph/Borders genes and is the actual link back to William Rolph (1787-1860) and Sarah Borders (1789-1869)³.

Figure 3: How incorrect trees can confuse ThruLines

Figure 3 shows the situation with the red dashed lines showing the genetic link as currently suggested by ThruLines and the green lines showing the actual genetic link, confirming the Rolph-Borders marriage as the MRCAs. Of course there is also a possibility of other, as yet undiscovered, links particularly in the sort of small, country villages inhabited by both the above examples.

The moral of this post is to always, ALWAYS double check anything in an online tree or suggested tree. Check for supporting documentation, check for reasonableness, check for alternative possibilities.

Sources

1. Ancestry ThruLines for Susan Law (https://www.ancestry.com.au/discoveryui-geneticfamily/thrulines/080AB020-82F7-4145-BC9C-3BF177830102?filterBy=all).
2. Burchall, Michael J. East Sussex Bastardy Papers 1594-1845 (CD ROM). Edited by The Parish Register Transcription Society. Lewes, UK: Sussex Family History Group, 2009.
3. Susan Law's Ancestry Tree (https://www.ancestry.com.au/family-tree/tree/52067358/family?cfpid=13296141854). Private tree, access by request.