"Perversions are defined as unnatural acts, acts contrary to nature, bestial, abominable, and detestable. Such laws are interpretable only in accordance with the ancient tradition of the English common law which ... is committed to the doctrine that no sexual activity is justifiable unless its objective is procreation." [A.C. Kinsey, et.al., "Sexual Behavior in the Human Male," 1948]
perversion per·ver·sion (pər-vûr'zhən, -shən)
A practice or act, especially one that is sexual in nature, considered abnormal or deviant.