I put to the Lumo chatbot:
Consider all of the expressive facial muscles available to the human being, and all of the recognized personality traits, and muse upon the possibility that certain personality traits tend to exercise specific sets of these muscles.
Lumo responded:
This is a fascinating intersection of anatomy, psychology, and evolutionary biology. Let me think through this systematically.
Humans have approximately 43 facial muscles dedicated to expression. These include the zygomaticus (smiling), corrugator supercilii (frowning/worry), orbicularis oculi (eye crinkling), frontalis (eyebrow raising), and depressor anguli oris (sadness/disgust), among others. Each can be activated independently or in combination, creating thousands of possible expressions.
Extraversion and the Smiling Apparatus Extraverts tend toward more frequent positive emotional displays. This would mean regular activation of the zygomaticus major and minor, plus the orbicularis oculi during genuine (Duchenne) smiles. Over years, this could create characteristic "laugh lines" around the mouth and eyes. Research does suggest extraverts display more animated facial expressions overall.
Neuroticism and Tension Patterns Higher neuroticism correlates with more frequent negative emotional states—anxiety, worry, irritability. This would engage the corrugator supercilii (brow furrowing), frontalis (forehead tension), and potentially the mentalis (chin tension). The colloquial "worry lines" between eyebrows aren't merely metaphorical; they reflect repeated muscle contraction patterns.
Agreeableness and Soft Expression Agreeable individuals typically show more warmth and less hostility. Their facial musculature might demonstrate more relaxed resting states, fewer defensive expressions (like the levator labii for disgust), and more frequent soft eye contact involving gentle orbicularis oculi engagement.
Conscientiousness and Control Conscientious people may exhibit more controlled, deliberate facial expressions—less spontaneous muscle activation, potentially more neutral resting faces. This could manifest as reduced overall facial movement variance.
Openness and Expressive Variety Those high in openness might show greater facial dynamism—more eyebrow raises (frontalis), varied expressions reflecting curiosity and engagement with novel stimuli.
Here's where it gets philosophically interesting: does personality shape the face, or does habitual expression shape personality? The facial feedback hypothesis suggests expressions can influence emotional states—a smile can genuinely improve mood. This creates a feedback loop where personality drives expression, expression reinforces neural pathways, and those pathways then influence future emotional responses.
I should note I'm not certain about the strength of empirical evidence here. While there's research on facial expressions and emotion, the specific connection between stable personality traits and chronic muscle usage patterns is less well-documented. Some studies suggest observers can partially identify personality from resting faces, but causation remains unclear.
From an evolutionary standpoint, this makes sense. Faces are communication devices. If certain personality traits consistently predict social behaviors, facial morphology adapting to facilitate those communications would be advantageous. A naturally agreeable person's face becoming more "approachable" through habitual expression serves social cohesion.
What aspect of this relationship interests you most—the anatomical mechanisms, the psychological implications, or perhaps whether we could train ourselves to change personality through facial exercises?