Biorhythms, deciduous enamel thickness, and primary bone growth: a test of the Havers‐Halberg Oscillation hypothesis

Abstract

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 human juveniles. We measured daily enamel growth increments to calculate RP in deciduous molars (n = 25). Correlations were sought between RP, molar average and relative enamel thickness (AET, RET), and the average amount of primary bone growth (n = 7) in humeri of age-matched juveniles. Results show a previously undescribed relationship between RP and enamel thickness. Reduced major axis regression reveals RP is significantly and positively correlated with AET and RET, and scales isometrically. The direction of the correlation was opposite to HHO predictions as currently understood for human adults. Juveniles with higher RPs and thicker enamel had increased primary bone formation, which suggests a coordinating biorhythm. However, the direction of the correspondence was, again, opposite to predictions. Next, we compared RP from deciduous molars with new data for permanent molars, and with previously published values. The lowermost RP of 4 and 5 days in deciduous enamel extends below the lowermost RP of 6 days in permanent enamel. A lowered range of RP values in deciduous enamel implies that the underlying biorhythm might change with age. Our results develop the intra-specific HHO hypothesis.

Developmental stress in South African hominins: Comparison of recurrent enamel hypoplasias in Australopithecus africanus and Homo naledi

“…While periodicity of striae of Retzius, and their surface expression as perikymata, are thought to be invariant for the individual, it may be that some teeth, particularly deciduous teeth, show different periodicities than do permanent teeth from the same individual. 39 Periodicity is reported to range in humans from 6 to 12 days in permanent teeth but, of these, 95% had periodicities between 7 and 10 days 40 with a mode of 8 days 41 . As yet, Retzius periodicities for H. naledi are unknown.…”

Histology of dental long‐period biorhythms in Canis familiaris

“…The RP values of 4 and 5 reported for deciduous teeth in studies by Mahoney and colleagues (Mahoney, 2011(Mahoney, , 2012Mahoney et al 2016) are certainly possible adult values for RP, as we have observed an RP of 5 in an adult Peruvians from archaeological context (Hogg & Bromage, 2018); therefore the low numbers reported for some deciduous teeth may mean nothing in and of themselves. If the numbers are anomalously low in deciduous teeth, this would be interesting but not relevant to the purported test of the HHO hypothesis by colleagues (Mahoney, 2011, 2012;Mahoney et al 2016) because the HHO model is based upon biological timing recorded in the permanent dentition.…”

“…A recent study (Mahoney et al. ) has argued that RP changes during the juvenile period, slowing down with the approach of adulthood; however, this conclusion is based on comparison of a very small sample of deciduous teeth against a much larger sample of permanent teeth drawn from multiple studies (Reid & Dean, ; Smith et al. ), so it is unclear currently if this finding is a statistical artefact.…”

“…If the numbers are anomalously low in deciduous teeth, this would be interesting but not relevant to the purported test of the HHO hypothesis by Mahoney and colleagues (Mahoney, , ; Mahoney et al. ) because the HHO model is based upon biological timing recorded in the permanent dentition.…”

“…A recent study (Mahoney et al 2016) has argued that RP changes during the juvenile period, slowing down with the approach of adulthood; however, this conclusion is based on comparison of a very small sample of deciduous teeth against a much larger sample of permanent teeth drawn from multiple studies (Reid & Dean, 2006;Smith et al 2007), so it is unclear currently if this finding is a statistical artefact. The RP values of 4 and 5 reported for deciduous teeth in studies by Mahoney and colleagues (Mahoney, 2011(Mahoney, , 2012Mahoney et al 2016) are certainly possible adult values for RP, as we have observed an RP of 5 in an adult Peruvians from archaeological context (Hogg & Bromage, 2018); therefore the low numbers reported for some deciduous teeth may mean nothing in and of themselves. If the numbers are anomalously low in deciduous teeth, this would be interesting but not relevant to the purported test of the HHO hypothesis by colleagues (Mahoney, 2011, 2012;Mahoney et al 2016) because the HHO model is based upon biological timing recorded in the permanent dentition.…”