They demonstrate that people with the founding lineage mitochondrial haplogroup were present in Mesoamerica at approximately 12,000 to 13,000 years ago — at a time consistent with the proposed timeline of the southward expansion.

They help to confirm that the movement of people from North America into Mesoamerica and beyond happened on the schedule that the genetics and the archaeology have independently suggested.

They also raise the question of what else is in the underwater caves of the Yucatán Peninsula.

The karst cave system is enormous — hundreds of miles of mapped passages, with more being added to the maps every year as cave divers continue their exploration.

Hoyo Negro is one chamber in a vast underground landscape that extends beneath one of the regions most densely populated by humans in the pre-Columbian Americas.