◌ ONE ORIGIN The story · The deep record · Scene 06

🧮 06 — SHARED DNA COMMON ANCESTOR COUNTER

Type a crowd. We’ll find the ancestor every one of them shares — twice over.

Two clocks run at completely different speeds. Follow the family tree and a crowd of 8 billion shares an ancestor roughly 33 generations back. Follow DNA — a single stretch of it — and the same crowd’s common ancestor is hundreds of thousands of years deep. Both answers are true. Enter any sample size, in any format.

Accepts 8 billion, 8,000,000,000, 300k or 8e9.

10,000
25

One random coalescent tree for a sample of that size (drawn with up to 48 tips; the maths behind the cards uses the whole sample). Watch the lineages merge: the last two lines to meet are the ancestor everyone in the sample shares.

Genealogical depth uses Chang’s 1999 result for a well-mixed population — the most recent common ancestor of a population of size N sits about log2N generations back, and the “identical ancestors point” about 1.77·log2N generations back. Ideal mixing is not the real world: with actual geography Rohde, Olson & Chang (Nature, 2004) put humanity’s shared ancestor nearer 3,000 years ago and the identical-ancestors point 5,000–15,000 years ago. Genetic depth uses the Kingman coalescent: E[pairwise] = 2Ne, E[TMRCA] = 4Ne(1 − 1/n), E[uniparental TMRCA] = Ne(1 − 1/n) generations. None of this describes you personally: it is a model of a sample, and Ne is a parameter, not a census.

More ways we’re connected

Sixteen ways to put the same point — that every human line on Earth runs back to one place — in your own hands.

Your own numbers

Your birthday crowdA date you share with millions. Your family treeMore branches. Shared roots. Your place, real sizeA fairer view of somewhere you love. A moment we shareDifferent clocks. Happening together.

The deep record

Two chains, one continentMitochondrial Eve and Y-chromosomal Adam, drawn against time. The shared ancestor counterType a crowd. Find the ancestor every one of them shares. Count the hands between usFewer than 50 links separate any two people alive. Fourteen peoples, one patternStructural universals across five continents.

Shifting the frame

Footsteps of KinshipDrag 300,000 years of leaving Africa, one toolkit at a time. Root to BranchThousands of languages branching from African roots. The Deep Time MirrorYour face, aligned with the oldest skulls we have. The Deep History Time MachineWatch borders, cities and farms fade off the planet. The Great-Grandparent MultiplierYour family tree has to loop. Here is the maths. Stardust & SoilWhat you are made of, and where each atom was forged. The Borderless Night SkySame stars. Many skies. One imagination. The Reverse Migration PostcardA line from your city back to the Great Rift Valley.

Feel the pattern

The Converging RiversEvery river runs back to the Rift. Drag to pull a thread home. The Synchronized BreathOne atmosphere. Hold to slow and breathe with the globe. The Shared LexiconMama, water, fire: one breath, many scripts. The Erasure of BordersScroll to peel the modern map down to a starlit Africa. The Mirror of AgesMany shades, one composite face. Unify the spectrum.

What every human does

Everybody SingsMusic was in all 315 societies the census read. All of them. The Same FaceBorn blind, never seen a face — and the same smile on winning. Two Hundred MillisecondsTen languages, five continents, one fifth of a second.