Variation in Modern Human Deciduous Molar Enamel Formation Time

Objectives: Histologically derived deciduous molar enamel formation times hold great potential for accessing information about
the prenatal and postnatal ontogeny of juvenile fossil hominins. Yet our understanding of these formation times in modern
humans is limited which inhibits comparative analyses. Here we utilize histology to investigate geographic and temporal variation
in prenatal, postnatal, and total enamel cusp formation times among modern humans. We examine some of the processes
whereby differences in formation time can arise by considering the underlying rate at which enamel forms and the average
amount of enamel that is produced.
Samples and Methods: Longitudinal thin sections of n = 356 deciduous first and second deciduous molars were selected
from eight populations. Present-day
samples were from the United Kingdom, North America, and Aotearoa New Zealand.
Archaeological samples represented the Medieval, Roman, and Iron Age periods. Formation times were calculated from prism
lengths and daily cross striations.
Results: Total cusp formation times for present-day
populations were similar except for Pacific Island peoples whose molars
formed over a relatively short period. Enamel cusps of the archaeological periods were complete on average 2.5 to 3 months ahead
of those from present-day
populations. Longer formation times were due to slower growth rates and an extended period of enamel
formation after birth. Enamel thickness varied only slightly between all populations.
Discussion: Our results reveal few differences in formation times between present-day
populations. Enamel formation was
complete relatively early in the archaeological samples, which we explore through shifts in the pace of somatic growth.