Unfortunately, science has few paleolithic penises to study. Due to this shortage, scientists have turned to the art of the time period in search of knowledge. In studying a wealth of phallic objects, a trend of geometric patterns and puncture marks can be witnessed (70% of the penis shaped objects had line designs, and 23% had piercings (they call them "pierced batons") ).These methods of ornamentation have lead some scientists to believe this may have been a reflection of how real bodies were also being decorated. In fact, piercing may have been a form of early medicine.
To learn more about
"Phallic Decoration in Paleolithic Art: Genital Scariﬁcation, Piercing and Tattoos" The Journal of Urology, 2011: