Biorhythms, deciduous enamel thickness, and primary bone growth in modern human children: a test of the Havers-Halberg Oscillation hypothesis

Across mammalian species, the periodicity with which enamel layers form (Retzius periodicity) in permanent teeth corresponds with average body mass and the pace of life history. According to the Havers-Halberg Oscillation hypothesis (HHO), Retzius periodicity (RP) is a manifestation of a biorhythm that is also expressed in lamellar bone. Potentially, these links provide a basis for investigating aspects of a species’ biology from fossilized teeth. Here, we tested intra-specific predictions of this hypothesis on skeletal samples of modern human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n=25). Correlations were sought between RP, molar average enamel thickness (AET), and the average amount of primary bone growth in humeri from age-matched juveniles.

Results show a previously un-described relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET, and scales isometrically. The scaling relationship could not be explained through body mass. Juveniles with higher RPs and thicker enamel had more primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was opposite to that predicted by the HHO. Next, we compared RP from deciduous molars to new data for permanent molars, and previously published values. The lowermost RP of four and five days in deciduous enamel was less than the lowermost value of six days in permanent enamel. A lowered range of RP values in deciduous enamel indicates that the underlying biorhythm might change with age. Our results develop the HHO.