Developmental Instability and Psychological Fitness: Can Morphological Asymmetry Predict Psychopathology?

Abstract

Developmental instability (DI) refers to an organism's failure to realize its ideal phenotype in a given environment. The most popular metric of DI is fluctuating asymmetry (FA), i.e., the degree to which bilateral morphological traits deviate from perfect symmetry when those traits are bilaterally symmetric per the ideal species phenotype. Numerous studies have shown that FA is inversely related to physical and reproductive fitness in myriad species of plants and animals. More recently, researchers have begun to assess correlations between FA and psychological variables in humans. Research has revealed negative relationships between FA and intelligence, neurological functioning, and typical brain structure. Positive relationships have also been found between FA and severe mental illness, such as schizophrenia. However, few studies have addressed the relationship between FA and symptomology of more prevalent forms of psychopathology, such as depression, anxiety, and alcohol abuse. The aim of this study is to address this void. Accordingly, FA was assessed in 204 college students across 12 morphological and dermatoglyphic traits. Current Axis I symptomology related to 13 diagnostic categories was assessed via the Psychiatric Diagnostic Screening Questionnaire (PDSQ). Depressive symptom severity was also assessed via the Beck Depression Inventory (BDI) in an attempt to replicate the previous finding of a positive relationship between FA and BDI in men (Martin et al., 1999). Finally, the SCID Axis II Screening Questionnaire (SCID-II-SQ) was administered to provide exploratory data regarding FA and personality disorders. Study analyses indicated two significant effects. In men, positive associations were identified between self-reported alcohol abuse and asymmetry in both dermatoglyphic constructs. However, Martin et al.'s (1999) observed positive association between FA and BDI score was not replicated. The multiple null findings are defended as valid, and consistent with evolutionary-based theories of psychopathology as stemming, in part, from adaptive ancestral mechanisms being expressed in novel, modern environments (e.g., Tooby & Cosmides, 2000). Criticisms of the existing FA literature are also presented.