Are Ancestry ThruLines Accurate? How to Verify Your Results

The short answer

ThruLines are not proof of anything. The DNA that Ancestry reports between you and a match is measured, but the family tree path linking you is largely assembled from trees that other members have built. Where those trees are well researched, ThruLines can be a useful and often correct pointer. Where they are copied or guessed, ThruLines can repeat the same errors with an air of authority.

A sensible way to think about it: ThruLines gives you a hypothesis to test. If you are new to the tool, our overview of how Ancestry ThruLines work explains the basics first.

Why ThruLines can be wrong

Errors in other people’s trees

Many online trees were built by copying from other trees. A wrong parent or a mixed-up pair of same-named people can spread widely. ThruLines uses those trees to propose connections, so a popular error can look well supported simply because many trees share it.

Small matches

Matches who share a small amount of DNA are more likely to be distant, and some small segments can be shared by chance without a recent common ancestor in any useful sense. Many genealogists treat matches in the lowest ranges with caution, and some are not confident in connecting them to a specific ancestor without other evidence. There is no single exact cutoff that everyone agrees on, so judge small matches case by case.

Descent through only one line

If every match supporting an ancestor descends through the same single child, the evidence is weaker than if matches descend through several different children of that ancestor. A single line can all trace back to the same mistaken tree.

Gaps filled from other trees

Dotted-box ancestors are suggestions drawn from other members’ trees. They are not entries you have researched, and they should be treated as leads.

Relationships that are not what they seem

Endogamy, where a population has long intermarried, can make people share more DNA than their documented relationship would suggest. Multiple relationships between the same families, half-relatives and unknown parentage can also confuse the picture. ThruLines does not always account for these.

Side assignment

For smaller matches, the grouping of which side of the family a match belongs to can be unreliable. Check this with other evidence, such as whether the match also matches known relatives on one side.

A step-by-step way to verify a ThruLines suggestion

Identify the claim. Write down exactly what is being suggested: which person is the proposed parent of whom.
Check the DNA first. Look at how much DNA you share with each match and whether the amount is plausible for the stated relationship. Ancestry’s relationship ranges overlap, so the estimate is a range, not a precise answer.
Count independent lines. Look for several matches descending through different children of the ancestor, rather than only one branch.
Check for a shared-match pattern. See whether the matches also match each other and your known relatives on the same side.
Search for original records. Look for civil registrations, church records, census entries, wills, probate files, land records and similar sources that name the parent-child link. Records created at the time of the event carry more weight than online trees.
Check for consistency. Do the dates, places and ages make sense? Look for impossible gaps, such as a parent too young or too old, or people in the wrong country at the wrong time.
Consider alternatives. Ask whether another person with a similar name could fit the same evidence.
Record your conclusion. Add notes and source citations to the person in your tree, and mark uncertain links as such. A genealogy research report template is a good way to write up your reasoning.

Warning signs

The suggested ancestor appears only in other people’s trees, with no document citations.
The only supporting matches are small and all descend through one child.
The suggestion puts someone in a place or time that does not fit what you know.
The proposed relationship contradicts a record you have already found.
The tree you are comparing with is missing sources entirely.

What to do when a suggestion fails

If your research contradicts a ThruLines suggestion, do not add the ancestor. If you have already added them, detach or remove the connection and note why. If the link is only unproven rather than disproven, you can keep a note in a research log and revisit it when new records or matches appear.

You can also contact the matches involved. Many people are happy to compare notes. Make sure your own tree is linked correctly first, since a wrong link can cause confusing results; see how to link your DNA results to your tree.

When ThruLines are most useful

ThruLines tend to be most helpful when:

the ancestor is in a well-documented line, such as in a country or period with good civil and church records,
many matches descend from the ancestor through different children,
the matches share larger amounts of DNA, and
you can confirm the key generations from documents.

They tend to be less reliable for brick-wall ancestors, sparse trees, and populations with extensive intermarriage.

Bottom line

Use ThruLines to generate ideas and find cousins, then confirm each link with records and independent DNA evidence. Treat every dotted box as unproven until you have done that work.