From Behavioral Ecology, an Oxford Journal:
The beard is a strikingly sexually dimorphic androgen-dependent secondary sexual trait in humans. Darwin posited that beards evolved in human ancestors via female choice as a highly attractive masculine adornment. Others have since proposed that beards evolved as a signal of male status and dominance. Here, we show that women from two very different ethnic groups, Europeans from New Zealand and Polynesians from Samoa, do not rate bearded male faces as more attractive than clean-shaven faces. Women and men from both cultures judge bearded faces to be older and ascribe them higher social status than the same men when clean-shaven. Images of bearded men displaying an aggressive facial expression were also rated as significantly more aggressive than the same men when clean-shaven. Thus, the beard appears to augment the effectiveness of human aggressive facial displays. These results are consistent with the hypothesis that the human beard evolved primarily via intrasexual selection between males and as part of complex facial communication signaling status and aggressiveness.