In the combination of these factors — the stable, cool salt water, the absence of surface-derived organic acids, the limited bacterial activity — lies the explanation for why bones twelve thousand years old in a flooded tropical cave preserved enough DNA for a haplogroup determination.

Most underwater tropical environments are actively hostile to organic preservation.

The specific chemistry of the Yucatán deep cave system created an exception.

The research team working on Hoyo Negro was aware that this preservation quality was unusual and potentially fragile.

Any disturbance to the chamber — increased water flow, changes in chemistry from surface contamination, physical disturbance of the sediment — could potentially damage the remaining preservation.

The decision to leave Naia’s bones in place was partly driven by preservation concerns: removing them would have exposed them to conditions less stable than the cave water, potentially accelerating the degradation of whatever biological material remained.