Their most significant objection was about DNA movement through sediment — the possibility that human DNA from later layers could have migrated downward through the cave sediment and become incorporated into older coprolites, making the ancient specimens appear to contain human DNA that was not present when the coprolites were originally deposited.

This is not a hypothetical concern invented to oppose unwelcome results.

It is a genuine phenomenon documented in multiple archaeological contexts.

DNA can move through sediment in several ways.

It can be carried by percolating water, which transports dissolved organic material downward through sediment profiles.

It can be carried by organic particles that are physically transported during periods when the sediment is disturbed or when the cave floor is wetted and dries.

And it can be transported by fungal networks — the mycelia that thread through soil and sediment can take up DNA from the environment and spread it horizontally and vertically in ways that bear no relationship to the original depositional context.