The human skull is a powerful symbol with a long history and multiple interpretations. Generally it represents death and mortality, but a skull can also be a symbol of caution, vanity, transition, courage, rebelliousness, nonconformity, luck, life after death, celebrating the memory of the dead, celebrating life, a fashion statement and decoration.
Part of the visual appeal of a skull comes from the fact that it is so easily recognizable. The human brain has a specific region for recognizing faces and is so attuned to finding them that it can see faces in a few dots and lines. With its large eye sockets, the human skull displays an almost childlike appearance, which humans find visually appealing. Yet, a skull is also obviously dead. Consequently, human skulls often have a greater visual appeal than the other bones of the human skeleton and can fascinate even as they repel. Until very recently, our society predominantly associated skulls with death and evil. However, to some ancient societies it was believed to have had the opposite association, where objects like crystal skulls actually represented life.
Historian, Harley Owners Club, Kingwood, Texas Chapter
Carlos Miller, The Arizona Republic
Gerald Erichsen, About.com