Genealogy Research: Prove Your Ancestry

1Your tree doubles every generation

Drag to orbit · slider grows the tree

Generations back from you: 4

You 12×back

4generations back

16ancestors that gen

30total ancestors

~120years back (≈30/gen)

6.25%expected DNA from one

At generation 4 you have 16 distinct ancestral slots (2⁴). Each one contributed on average 6.25% of your autosomal DNA — because every generation back roughly halves the expected share (50% → 25% → 12.5% → ...).

2Sources: primary vs secondary

Every claim in your tree should rest on evidence, and not all evidence is equal. Genealogists weigh sources by how close they are to the event.

What makes a source trustworthy
Source type	Examples	Strength
Primary (original, recorded at the time by a participant/witness)	Birth & death certificates, marriage registers, wills, land deeds, ship manifests	Highest — created near the event
Secondary (recorded later or by a non-witness)	Later censuses, obituaries, published family histories, compiled trees	Supporting — verify against originals
Derivative (a copy or transcription)	Index entries, transcribed databases, online abstracts	Clue only — trace to the source image

Census (every 10 yrs) Vital records Church registers Wills & probate Land & deeds Military & pension Immigration

A single source is rarely enough. The U.S. census, for instance, was often reported by a neighbor and ages drift year to year — treat one record as a clue, then corroborate with an independent source before you trust it.

3The Genealogical Proof Standard

Professional genealogists don't declare a link "proven" on a hunch. The Genealogical Proof Standard (GPS) — from the Board for Certification of Genealogists — sets five conditions that must all be met.

1Reasonably exhaustive research. Search all sources that might answer the question, not just the easy online ones.

2Complete, accurate citations. Every fact is cited so anyone can re-find the source and judge it.

3Analysis & correlation. Weigh each source's reliability and compare evidence side by side.

4Resolve conflicts. When records disagree (two birth years!), explain and resolve the contradiction with evidence.

5Soundly reasoned, written conclusion. State the proof argument clearly so it can be reviewed.

Worked example. To prove "Mary Kelly (1848) is the daughter of John Kelly," you might combine a baptism register (primary), the 1851 census placing Mary in John's household, John's will naming "my daughter Mary," and a DNA match to another Kelly descendant. Four independent strands that agree = a sound conclusion.

4How DNA complements paper

Autosomal DNA & centimorgans

Autosomal DNA tests (AncestryDNA, 23andMe, MyHeritage) compare the 22 non-sex chromosome pairs you inherit from both parents. Shared DNA is measured in centimorgans (cM) — a unit of genetic distance. The more cM two people share, the closer the relationship.

Typical shared autosomal DNA
Relationship	≈ % shared	≈ cM (of ~6800)
Parent / child	50%	3400
Full sibling	~50%	2600 (range)
Grandparent	25%	1700
1st cousin	12.5%	850
2nd cousin	3.125%	~230
3rd cousin	0.78%	~75

Why DNA fades going back

Each generation you inherit a random half of each parent's DNA. So expected shared DNA halves each step back: 50% (parent) → 25% (grandparent) → 12.5% (great-grandparent).

By ~6 generations back, an ancestor's expected contribution is under 1.6% — and by chance you may inherit zero detectable DNA from some distant ancestors.
DNA can confirm or break a paper link (uncovering misattributed parentage), but it rarely names a specific ancestor by itself.
Best practice: use DNA and documents together — matches point you to record searches, records explain the matches.

DNA cuts both ways: it can reveal an unexpected relationship. Approach results with care and respect for living relatives' privacy.