Childhood stress and developmental instability: Comparing microscopic enamel defects and cranial fluctuating asymmetry in a colonial Mexican sample

Abstract

AbstractObjectivesRecent tests of the relationship between enamel defects, an indicator of early life stress, and fluctuating asymmetry (FA), a measure of cumulative developmental instability, have produced equivocal results. This may be because they use methods that underestimate the number of defects. We reinvestigate this relationship using high‐resolution microscopy images of tooth surfaces. Further, we test the hypothesis that developmental stresses during the earliest period of tooth development have a greater impact on FA than stresses during subsequent periods.Materials and MethodsThe sample consists of 48 individuals from two colonial‐era cemeteries in Mexico City. Using one canine from each individual, we created photomontages using a 2D light microscope. Tooth crowns were divided into three developmental periods. Defects were identified as widely spaced perikymata using moving z‐scores. We compared defect presence, frequency, and timing to FA calculated from 11 landmarks using geometric morphometrics from 3D models of each cranium.ResultsBoth the presence and frequency of enamel defects are significantly associated with an increase in FA. Contrary to our expectations, defects that formed in the latest developmental period (4–5.5 years) were uniquely associated with an increase in FA, relative to the other two periods.DiscussionThe presence and frequency of stress during childhood increases developmental instability. The time between 4 and 5.5 years may be a sensitive window of development in which disruptions to growth have a long‐lasting effect on developmental instability. Results indicate that research on developmental stress should consider the timing and frequency of stress events to more fully understand their impact on later life.