If you can't find records about your direct ancestor, researching their siblings and cousins often reveals the same information—marriage dates, children's names, migration patterns—all documented in public records for the collateral branches. You're using the family you can prove to establish facts about the ancestor you can't.
Collateral line research is the practice of tracing the siblings, cousins, and other non-direct relatives of an ancestor in order to gather evidence that resolves questions about the direct line. When records for a great-grandparent are missing or ambiguous, the records of that person's brothers or sisters frequently preserve shared parental names, birthplaces, or immigration details.
AI tools can help genealogists build out collateral lines efficiently by suggesting which relatives to pursue based on existing tree data, locating their records across databases, and using those findings to generate logical inferences about the direct ancestor in question.
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