In a study, which can only be presumed be a publicity stunt to help boost sales of razors*, it has been suggested that men who display significant ornamentation - such as beards - are more likely to have smaller testicles.
The study, entitled Sexual Ornaments But Not Weapons Trade Off Against Testes Size In Primates, was conducted in collaboration by researchers at the University of Western Australia and at the University of Zurich.
The study assessed aspects of male reproduction across around 100 species of primates, including humans. They sought to investigate the relationships between male tactics for reproduction by comparing whether male primates that invested time into traits that 'promoted access to femals' versus specifically reproductive traits that enhance fertilization success.
One finding of the study was to highlight that the size of male primates testes were relatively smaller on individuals who exhibited greater sexual ornamentation, which - in the case of humans - would constitute a large beard for example.
Given that the association is not causal ie. male primates do not have smaller testes because grow beards, the desire for this sexual ornamentation implicitly stems from the fact that they have smaller testes. They found that it was more advantageous for these males to invest in sexual ornamentation as a means of attracting mates.
One of the scientists who co-authored the paper, Dr. Cyril C. Grueter, said of the findings, “Some species sport flamboyant accoutrements such as beards, manes, capes and cheek flanges, and various shades of colour in their faces and fur, others are pretty drab and look more like your ‘Mr Average’.
“This finding clearly shows that you can be well adorned or well endowed, but it’s hard to be both,” concluded Dr. Grueter.
Well, I'm sure you won't be surprised if this finally rings the death knell for the ever-pervasive beard trend.