Its preservation over any significant time period requires conditions so unusual that such preservation has been reported only in exceptional circumstances — extremely cold environments, extreme aridity, very specific chemical conditions.

That preserved intracranial tissue of any kind was found in skulls from a warm, humid, subtropical Florida environment, approximately 8,000 years after the deaths of the individuals, was genuinely astonishing to the researchers who encountered it.

It is important to be precise about what was found.

The 1986 Nature paper by Doran, Dickel, and their colleagues described the findings from the material recovered during the first two field seasons — 1984 and 1985.

The paper reported that of the minimum-40 individuals recovered from that early sample, nine had intracranial soft matter preserved within the skull.