How common is sexual sadomasochism in individuals?

Excluding: Bondage and discipline, as well as dominance and submission. Strictly sadists, masochists, and sadomasochists. Is it more common to be a sadist, masochist, or a sadomasochist?
Also, why do some individuals solely express sexual sadomasochism, while others are affected in numerous aspects of their lives? Is there any kind of evolutionary psychological explanation?