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

Abstract

Objectives Recent 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 Methods The 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. Results Both 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. Discussion The 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.

Skeletal age during hurricane impacts fluctuating asymmetry in Cayo Santiago rhesus macaques

“…To this end, the impact of developmental instabilities on FA is thought to be magnified during ontogeny, such that the impact of early-life adversity may contribute more strongly to FA than hardship experienced when the skeleton has already been formed (Gluckman & Hanson, 2006;Hallgrímsson, 1999). This theory is substantiated by recent work into the human cranium, which highlights a window of vulnerability to developmental instability occurring between 1 and 5.5 years of age, with a uniquely sensitive time between 4 and 5.5 years (Moes et al, 2022).…”

Using craniofacial fluctuating asymmetry to examine the effects of sex, socioeconomic status, and early life experiences on adult age at death in industrial England

“…Similarly, some scholars have suggested that other social categories, such as sex (as a proxy for gender), could play a critical role, causing individuals who experience sex-or gender-based discrimination or stress to develop higher levels of FA compared to their peers who are buffered by more privileged social positions (Jung et al, 2016). A final note about seemingly conflicting findings in bioarchaeological research of craniofacial FA YAUSSY comes from Moes et al (2022), who suggest that the timing and duration of developmental stress events may play a role in the patterns of FA observed among adults. Specifically, Moes et al (2022) find that enamel defects indicating developmental stress events between 4 and 5.5 years of age were associated with higher levels of FA compared to enamel defects signaling stress during earlier developmental windows.…”

“…A final note about seemingly conflicting findings in bioarchaeological research of craniofacial FA YAUSSY comes from Moes et al (2022), who suggest that the timing and duration of developmental stress events may play a role in the patterns of FA observed among adults. Specifically, Moes et al (2022) find that enamel defects indicating developmental stress events between 4 and 5.5 years of age were associated with higher levels of FA compared to enamel defects signaling stress during earlier developmental windows.…”

“…In recent years, bioarchaeological studies have also addressed the potential for FA to serve as a skeletal indicator of early life stress, which can be used to evaluate bioarchaeological support for the DOHaD hypothesis. Particularly, these studies recognize that FA is the result of trade‐offs during periods of stress that facilitated short‐term survival at the cost of reduced energy allocation to growth and development, and this enduring metric of developmental instability can be connected to adult health outcomes observable in human skeletal remains (O'Donnell & Moes, 2021; Moes et al, 2022). For example, in a study of childhood health indicators and adult mortality, Watts (2013) found that cribra orbitalia presence and FA values corresponded with earlier mortality in females living in northern England prior to 1700 A.D. Interestingly, this association between FA and early mortality was not maintained in individuals who lived after 1700 A.D., and Watts (2013) suggests that environmental and economic changes in the post‐1700 A.D. period protected that population from the early mortality associated with developmental insults seen in the pre‐1700 A.D. period.…”

“…A final note about seemingly conflicting findings in bioarchaeological research of craniofacial FA comes from Moes et al (2022), who suggest that the timing and duration of developmental stress events may play a role in the patterns of FA observed among adults. Specifically, Moes et al (2022) find that enamel defects indicating developmental stress events between 4 and 5.5 years of age were associated with higher levels of FA compared to enamel defects signaling stress during earlier developmental windows. In sum, previous research suggests it may behoove bioarchaeological studies of FA to consider more than one category of social marginalization as a potential source of or moderator of differential developmental stress among populations or population subgroups.…”