Long period growth lines in enamel and body size in humans: a test of the Havers-Halberg Hypothesis

According to the Havers-Halberg Oscillation hypothesis (HHO), evidence of a metabolic biorhythm retained in enamel as Retzius periodicity (RP) positively correlates with average body mass and the pace of life history across the majority of mammalian species. In humans, RP is highly variable between individuals, but it is unknown if it correlates with body size, as it does across species. Here, stature and body mass was estimated in an archeological sample of modern humans (n=23). Retzius periodicity was reconstructed for permanent teeth from the same individuals. Reduced major axis regression revealed that RP is significantly and negatively correlated with stature and body mass in adult humans. Individuals with higher RPs were of smaller stature and body mass than those with lower RPs. These results support an intraspecific HHO hypothesis, whereby increases in body size within humans are achieved through an accelerated biorhythm, and reflected by a lower RP. Results presented here lay a new foundation for studies of enamel histology and life history within modern humans, with potential applications to our fossil ancestors.