The appropriate expert panel to review this topic would be Human Behavioral Ecologists and Evolutionary Psychologists.

Abstract:

This analysis, led by human behavioral ecologist Dr. Barnaby Dixson, investigates the evolutionary mechanisms underlying human male facial hair (beards), treating it as a complex case study in sexual selection that defies simple analogies to classic ornamental displays (e.g., the peacock’s tail). Empirical research indicates attractiveness preferences for beards among heterosexual women are highly variable and context-dependent, with overall effect sizes being small to trivial, often showing a non-linear preference for thick stubble (10 days) over full beards or clean-shaven faces. Stronger, unambiguous effects are observed in intrasexual competition contexts, where beards function as robust signals of age, sexual maturity, dominance, and aggression. Null findings were observed for the ovulatory shift and parasite stress hypotheses. However, strong experimental evidence supports a negative frequency dependence effect, where the rarity of a specific beard style temporarily increases its attractiveness. Critically, the unique hormonal pathway governing beard growth (dihydrotestosterone dependence) suggests it acts as a potentially dishonest signal of physical formidability compared to crania-facial masculinity. The finding that new mothers rate bearded men higher on parental investment and nurturing qualities challenges the traditional "masculinity trade-off" narrative in human mate choice.

Summarization:

• 0:00 The Darwinian Puzzle: The evolution of the beard is presented as a paradoxical trait, similar to the peacock’s tail, because its ostentatious, seemingly costly, and impractical nature (5:59) suggests strong sexual selection, yet its function is unclear.
• 9:43 Attractiveness Findings are Mixed: Studies on beard attractiveness are split approximately 50/50 among women. Preferences are generally non-linear, with thick stubble (10 days) often rated as the most attractive facial hair level (13:17), suggesting cultural intervention (grooming) is crucial to optimizing the trait's appeal.
• 18:13 Null Hypotheses: Dr. Dixson reports null findings for several established evolutionary psychology hypotheses when applied to beards:
  • Ovulatory Shift Hypothesis (18:19): No significant increase in preference for beards during women's periovulatory fertile phase.
  • Parasite Stress/Pathogen Avoidance (20:22): Priming participants with images of bugs/parasites yielded no change in beard preferences, rejecting the idea that "clean shaven" signals freedom from ectoparasites.
• 23:57 Frequency Dependence Demonstrated: Experimental evidence supports that preferences for facial hair styles (shaven, stubble, bearded) are negatively frequency dependent (29:23). When a particular style is rare, it is rated as significantly more attractive, aligning with historical cyclical fashion trends observed over 150 years (26:59).
• 35:31 Ecological Predictors of Beard Frequency: Men in higher population density areas with greater income disparity exhibit higher rates of beardedness, suggesting beards are prioritized for signaling sexual maturity and status in highly competitive socioeconomic environments (38:00).
• 45:01 Beard/Facial Masculinity Interaction: Beards can either augment an already masculine face or, more interestingly, act as a masking effect (47:30) for men with less mature or more feminine facial features. The beard universally increases perceived age and maturity (47:56).
• 57:49 Beards Signal Dominance and Threat: The most robust finding across studies and cultures (Samoa and New Zealand) is that beards significantly increase perceptions of social dominance, aggressiveness, and threat (58:33). Participants are faster and more accurate at assigning "anger" to bearded faces than clean-shaven ones (1:01:15).
• 1:07:47 Beard as a Dishonest Signal: Unlike crania-facial masculinity, which correlates with upper body strength (1:04:01) and requires high circulating testosterone, beard growth relies on the conversion of testosterone to dihydrotestosterone via the 5-alpha reductase 2 enzyme (1:09:08). This biological difference means beards are not an honest signal of underlying physical formidability (1:11:15).
• 1:17:44 Null Finding for Defensive Function: Analysis of high-intensity conflict data (UFC/MMA fighters) found no statistical evidence that beards function as a regenerative protective buffer against injury (like a lion’s mane) or as a fighting handicap (grab handle) (1:19:10).
• 1:32:04 Challenge to the Masculinity Trade-Off: While masculine traits are typically theorized to signal good genes but poor parental investment, beards contradict this. New mothers (with infants under one year old) rate bearded men significantly higher on dimensions of parental investment and nurturance than women without children (1:33:48), suggesting beards may signal long-term investment viability.
• 1:42:25 Conclusion on Signaling: Beards unambiguously communicate basic traits (biological male, sexually mature, adult status) but exhibit small, variable effect sizes for sexual attraction. Their large effect sizes are consistently found in the domain of intrasexual signaling (dominance/aggression) and, surprisingly, paternal quality (1:46:15).