Background: Living matter has its own ‘biological time’: a set of rhythmic oscillations, paced by genes whose expression varies over regular cycles. The resulting chronomes, or time structures, are usually
studied in living matter. A human chronome is preserved long after death in the structure of tooth enamel. This fossil record can be compared with contemporary enamel thus providing insight into an ancient biological rhythm, and consequently into behavior in pre-historic civilizations.
Material/Methods: Eight adult 3rd molar teeth from human burials in Atacama oases of Northern Chile, dating from AD 400 to 900 and belonging to the pre-Hispanic San Pedro culture, were compared to
20 discarded contemporaneous teeth from Albuquerque, N. M. USA. Two adjacent, 100 µm thick ground sections from each tooth were examined using a stereoscopic dissecting microscope and polarized light. The intervals between consecutive brown striae of Retzius (TBS)
and the width of the enamel were measured. We recorded the number of TBS and the number of Wilson’s bands and calculated a ratio of enamel width/number of TBS for each section. We used ANOVA for statistical analysis and cosinor methodology for chronomics, time structure (chronome) mapping.
Results: The ‘biological week’ in the chronome (time structure) of ancient enamel, gauged by TBS, varied according to a multiseptan (multiple of seven) component faster than did the multiseptan
of contemporaneous teeth (1/2.7 versus 1/4.6 biological weeks).
Conclusions: Until now no human chronome has been isolated from fossilized structures. Our discovery indicates that behavior of ancient populations, such as rest and work spans, can be deduced to
some extent after millennia.

Keywords: Behavior, Biological Clocks, Dental Enamel - cytology, Dental Enamel - growth & development, Dentition, Fossils, Paleontology, Time Factors