Meta-analysis reveals weak associations between intrinsic state and personality

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Individual differences in behavior, or personality, are observed across species.
• Behavioral ecology theory suggests that intrinsic physiological states influence behavior.
• Metabolism, hormones, and body size are proposed as key intrinsic states.

Purpose of the Study:

• To quantify the extent of among-individual variation in behavior attributable to variation in intrinsic states.
• To critically evaluate the empirical support for state-dependent personality theory.

Main Methods:

• Conducted a meta-analysis of studies investigating the association between intrinsic states and behavior.
• Assessed the proportion of studies that appropriately measured individual-level associations.
• Synthesized findings on correlations between behavioral traits (aggression, boldness, activity) and physiological states.

Main Results:

• Only 22% of reviewed studies appropriately estimated individual-level state-behavior associations.
• Individuals exhibiting higher levels of aggression, boldness, exploration, or activity generally had higher metabolic rates, hormone levels, body weight, and/or body size.
• The proportion of behavioral variation explained by intrinsic states was small, approximately 5%.

Conclusions:

• Current adaptive explanations involving intrinsic states inadequately account for individual behavioral variation.
• Future research should explore nonlinear, additive, or interactive effects of multiple intrinsic states.
• Alternative explanations for behavioral variation, or improved empirical testing of existing theories, are necessary.