Genealogy Day

What the day is

Genealogy Day is observed on March 13. Family history has been transformed twice in a generation, first by digitized records and then by cheap DNA testing, and the second is more easily misread than the first.

Origin and background

The ancestry percentages a testing company reports are estimates produced by comparing your DNA against reference panels of people with known recent origins. They are not a readout of your lineage. Different companies give different answers for the same sample, results shift when reference panels are updated, and regions with thin reference data produce coarse results. The percentages are a statistical comparison, not a measurement.

The underlying biology limits things further. Because DNA is inherited in chunks rather than evenly, you carry no detectable DNA at all from a substantial share of your ancestors once you go back several generations. Your family tree doubles every generation while your genome does not, so beyond about seven or eight generations most of the people in your tree left no genetic trace in you. A documented paper trail reaches places a test cannot.

Where DNA testing is genuinely powerful is close relationships. Matching lists reliably identify cousins, and this has produced real consequences: large numbers of people discovering unknown siblings, misattributed parentage or donor conception, often without warning. Testing companies now carry advisories for exactly this reason, and it is worth considering before testing rather than after.

The documentary side rewards ordinary method. Census returns, parish registers, military and shipping records are increasingly indexed, and the standard discipline is to work backward one generation at a time, record each source, and treat an online tree assembled by a stranger as a lead rather than evidence.

How to take part

• Interview the oldest person in your family, and record it.
• Work backward one verified generation at a time rather than leaping.
• Cite where every fact came from, which is what separates research from a guessed tree.
• Treat ancestry percentages as estimates that will change.
• Think about what a DNA test might reveal before ordering it.