In research reconstructing patterns of health in skeletal remains, non-destructive biomarkers of stress can be studied at different ages to reflect specific windows of development (McPherson, 2021, Temple, 2019). Teeth are ideal sources of these biomarkers due to their well-documented timing of development, and because they preserve relatively well in archaeological contexts. Fluctuating asymmetry (FA), a measure of random differences from bilateral symmetry, has received attention bioarchaeological research for its use as an indicator of developmental stress. FA is thought to reflect developmental instability from physiological disruption (Van Valen, 1962) where asymmetry is a plastic response to an individual’s inability to buffer against energetic disturbances (Farrera, 2022, Gangestad, 2022, Van Dongen and Gangestad, 2011).

When studying the relationship between dental FA and documented stress, findings have been inconsistent, resulting in varied interpretations as they relate to our understanding of how early life stress is connected to later health (e.g. Graham & Özener, 2016; Kohn et al., 2025). In modern settings, high dental FA has been linked to maternal alcohol consumption, obesity and smoking during pregnancy (Kieser, 1992, Kieser et al., 1997), but not to birthweight (Apps et al., 2004, McPherson et al., 2024) nor environmental radiation exposure (Angelopoulou et al., 2009). In archaeological research that compares FA across time periods or populations, some studies confirm their predictions of stress that are based on other skeletal or archaeological evidence (e.g., (Barrett et al., 2012; Guatelli-Steinberg et al., 2006; Wigley et al., 2025). Lack of or weak results are often interpreted as evidence of resilience or biocultural buffering strategies (e.g., Hoover & Hudson, 2016; López-Onaindia & Subirà, 2020; Milella et al., 2018; O’Donnell & Moes, 2021).

Research on the developmental origins of health and disease in skeletal remains emphasizes the incorporation of ontogeny and life history to improve studies of developmental stress (e.g., (Corron et al., 2025; DeWitte et al., 2025; McPherson, 2021; Moes et al., 2022; Temple, 2019). Dental FA research often fails to support this approach because FA is traditionally regarded as a biomarker of chronic or accumulated stress rather than being tied to specific biological stages during development. By understanding how the timing of stress exposure interacts with periods in which developing dental tissues are especially sensitive to disruption, we can significantly improve the utility of FA as a marker of early life stress. Developing teeth are known to be impacted by childhood experiences such as illness, nutrition levels, and parental socioeconomic status (SES) where there are changes to enamel growth (Rugg-Gunn et al., 1998, Ungar et al., 2017, Za̧dzińska et al., 2013), and tooth eruption timing (Alnemer et al., 2017, Mennella et al., 2020, Ządzińska et al., 2016). We must test if such early life stresses are also related to dental FA formed during narrow windows to understand how, when, and under what circumstances such stress is embodied in the shape and size of teeth.

The inconsistencies in the relationship between dental FA and developmental stress across the literature may be attributed to how stability, plasticity, and noise vary between and within developmental systems (Aparicio and Bonal, 2002, Graham, 2021, Klingenberg, 2019). Crown dimensions and shape are known to be under varying degrees of genetic control within and between each tooth class (Khalaf et al., 2005, Paul et al., 2022, Townsend et al., 2003), resulting in varying degrees of susceptibility to developmental disruption. For example, crown dimensions are considered to be more environmentally stable than molar intercuspal distances (Townsend et al., 2003). The inconsistent correlations between dental FA and environmental stresses are likely caused by a lack of standardized trait and tooth selection. Because traits chosen in dental FA calculations often vary in their developmental timing (AlQahtani et al., 2010, Reid and Dean, 2006), the windows in which they are sensitive to disruption will not necessarily coincide with the stressor(s) under consideration.

Further complicating our understanding of FA as an indicator of stress, there are inherent differences between the sexes in plastic responses to physiological disruption, likely due to their varying investment strategies in early development (Meakin et al., 2021). Because the literature shows little or no evidence of sex differences in dental FA (Guatelli-Steinberg et al., 2006, Khalaf et al., 2005, Milella et al., 2018, Wigley et al., 2025), sexes are often pooled for analyses (Barrett et al., 2012, O’Donnell and Moes, 2021). However, analyzing males and females together in FA research may not be appropriate given inherent sex differences in tooth structure. For example, females have thicker enamel and males have a larger dentine component in their teeth, which drives their larger crown dimensions, especially in canines (Fernée et al., 2021, García-Campos et al., 2018). Therefore, there is likely sexual dimorphism in responses to stress based on dental tissue and tooth type. Studies of FA will consequently be influenced by the teeth and traits included in the analyses.

The goal of this study is to determine associations between early life stress exposures and various measures of FA in the permanent dentition. Using data from a 20th century growth study, we combine insights about developmental biology with documented records of gestation, birth, and childhood to strengthen our ability to interpret stress in the archaeological record by considering the effects of the environment on children’s dental development. Because FA may be driven by disruptions that occur during specific windows of susceptibility and/or by variation in trait stability, we examine multiple measures of FA to test which combination(s) of traits are reflective of early life. This novel approach tests both factors as potential drivers of variation in tooth shape and size. With this approach, we may be able to improve the use of dental FA as a reliable indicator of early life stress by identifying which traits should be examined. Furthermore, recognizing variation in dental traits that are tied to narrow windows of development which co-occur with documented stressors may expand our understanding of dental plasticity during the earliest stages of tooth development.

We create several indices of FA separated by the ages at which traits are developing, as well as by types of measurements (crown dimensions and intercuspal distances). These indices reflect FA measured in traits that complete development in the following windows: 0–1 year, 1.5–3.5 years, 4–7 years, and 1–7 years. Because the first 1000 days after conception are widely recognized as a critical window (Schwarzenberg & Georgieff, 2018), we predict that 1) factors throughout gestation and the first two years of postnatal life will be associated with increased FA in all indices, and 2) that these relationships will vary between males and females based on the traits and teeth used in each index.