Gender differences in smiling: An evolutionary neuroandrogenic theory.

Area of Science:

• Evolutionary Psychology
• Neuroendocrinology
• Behavioral Biology

Background:

• Females exhibit higher smiling frequencies than males across diverse social contexts.
• Existing research indicates sex differences in social signaling and emotional expression.

Purpose of the Study:

• To propose a theoretical framework explaining why females smile more than males.
• To investigate the role of testosterone in modulating male smiling behavior and its evolutionary underpinnings.

Main Methods:

• Theoretical modeling based on evolutionary principles of mate selection and resource competition.
• Review of existing neurobiological and behavioral evidence related to sex hormones and social behavior.
• Derivation of testable hypotheses for future empirical research.

Main Results:

• The theory posits that testosterone inhibits male smiling by altering brain function, particularly in reproductively active males.
• Male smiling is hypothesized to interfere with intimidating rivals during resource competition, a trait favored by females for provisioning.
• Genes on the Y-chromosome may promote resource competition by inhibiting submissive signals, with testosterone influencing hemispheric brain activity.

Conclusions:

• Testosterone's influence on brain function may explain sex differences in smiling, linking it to evolutionary pressures for male resource acquisition and competition.
• The theory suggests a neurobiological mechanism where testosterone shifts cognitive processing away from "prosocial" left-hemispheric functions towards the right hemisphere.
• Further research is needed to empirically test the derived hypotheses regarding testosterone, Y-chromosome genes, and social signaling in males and females.