Developmental instability, fluctuating asymmetry, and human psychological science

Area of Science:

• Psychology
• Developmental Biology
• Behavioral Genetics

Background:

• Developmental instability (DI) reflects an organism's inability to buffer random developmental perturbations.
• Fluctuating asymmetry (FA), the deviation from symmetry in bilateral traits, is a common proxy measure for DI.
• Psychological research has explored FA associations with various outcomes for decades.

Purpose of the Study:

• To review the associations between fluctuating asymmetry (FA) and psychological outcomes.
• To assess the methodological limitations, particularly statistical power, in FA research.
• To identify future directions for understanding developmental instability (DI) in psychology.

Main Methods:

• Meta-analysis of nearly 100 studies examining FA and psychological traits.
• Review of literature published over the past decade, noting methodological trends.
• Assessment of statistical power in individual studies and across the field.

Main Results:

• Small but statistically significant associations between FA and psychological traits are consistently found.
• Existing associations likely underestimate the true relationship between DI and psychological outcomes.
• Many studies, including recent ones, suffer from insufficient statistical power, leading to noisy data.

Conclusions:

• Despite modest effect sizes, FA remains a relevant, albeit imperfect, indicator of DI in psychological research.
• Underpowered studies hinder progress; large-scale investigations are crucial for robust findings.
• Revising theoretical frameworks and improving methodological rigor are essential for advancing DI research in psychology.