And then, in even more modern times, researchers extracted tiny cores of material from the densest bones of the smallest skulls and sent them to laboratories where machines read the fragments of ancient DNA — fragments that had survived the centuries because the petrous bone had held them against the dissolution that claimed the rest.

The limestone kept the secret for five centuries.

The science read it.

Two pairs of twins were known for the first time in the modern world as twins — separated from that knowledge by the long years and the long darkness, and then found again in the sequences of a genome.

The Full Circle

The finding of two pairs of identical twins in the Chichén Itzá chultún is, at one level, a statistical result: a coefficient of relatedness approaching one, a genome-wide comparison that identified four individuals as two pairs of monozygotic twins.

At another level, it is a human story.