If monozygotic twins occur at roughly 3 to 4 per 1,000 births, and if in a group of 64 individuals we find not just one pair but two pairs — meaning that 4 of the 64 are members of monozygotic twin pairs — the departure from chance expectation is striking.

In a randomly assembled group of 64 individuals drawn from a large population, the probability of finding even one pair of identical twins present together is low; the probability of finding two pairs is lower still.

The two pairs of twins in the Chichén Itzá chultún were not there by accident.

Their presence reflects whatever process of selection determined who was interred in this underground ritual feature over the centuries of its use.

What Genomics Cannot Resolve